Java.lang.Class class in Java | Set 1

Java provides a class with name Class in java.lang package. Instances of the class Class represent classes and interfaces in a running Java application. The primitive Java types (boolean, byte, char, short, int, long, float, and double), and the keyword void are also represented as Class objects. It has no public constructor. Class objects are constructed automatically by the Java Virtual Machine(JVM). It is a final class, so we cannot extend it.

The Class class methods are widely used in Reflection API.

Creating a Class object

There are three ways to create Class object :

  1. Class.forName(“className”) : Since class Class doesn’t contain any constructor, there is static factory method present in class Class, which is Class.forName() , used for creating object of class Class. Below is the syntax :
    Class c = Class.forName(String className)
    

    The above statement creates the Class object for the class passed as a String argument(className). Note that the parameter className must be fully qualified name of the desired class for which Class object is to be created. The methods in any class in java which returns the same class object are also known as factory methods. The class name for which Class object is to be created is determined at run-time.

  2. Myclass.class : When we write .class after a class name, it references the Class object that represents the given class. It is mostly used with primitive data types and only when we know the name of class. The class name for which Class object is to be created is determined at compile-time. Below is the syntax :
    Class c = int.class
    

    Please note that this method is used with class name, not with class instances. For example



    A a = new A();   // Any class A
    Class c = A.class; // No error
    Class c = a.class; // Error 
    
  3. obj.getClass() : This method is present in Object class. It return the run-time class of this(obj) object. Below is the syntax :
    A a = new A();   // Any class A
    Class c = a.getClass();
    

Methods:

  1. String toString() : This method converts the Class object to a string. It returns the string representation which is the string “class” or “interface”, followed by a space, and then by the fully qualified name of the class. If the Class object represents a primitive type, then this method returns the name of the primitive type and if it represents void then it returns “void”.
    Syntax : 
    public String toString()
    Parameters : 
    NA
    Returns :
    a string representation of this class object.
    Overrides :
    toString in class Object
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate toString() method
    public class Test
    {
        public static void main(String[] args)
                             throws ClassNotFoundException
        
            // returns the Class object for the class 
            // with the specified name 
            Class c1 = Class.forName("java.lang.String");
            Class c2 = int.class;
            Class c3 = void.class;
              
            System.out.print("Class represented by c1: ");
             
            // toString method on c1
            System.out.println(c1.toString());
              
            System.out.print("Class represented by c2: ");
              
            // toString method on c2
            System.out.println(c2.toString());
              
            System.out.print("Class represented by c3: ");
              
            // toString method on c3
            System.out.println(c3.toString());
        }
    }

    chevron_right

    
    

    Output:

    Class represented by c1: class java.lang.String
    Class represented by c2: int
    Class represented by c3: void
    
  2. Class<?> forName(String className) : As discussed earlier, this method returns the Class object associated with the class or interface with the given string name. The other variant of this method is discussed next.
    Syntax : 
    public static Class<?> forName(String className) throws ClassNotFoundException
    Parameters : 
    className - the fully qualified name of the desired class.
    Returns :
    return the Class object for the class with the specified name.
    Throws :
    LinkageError : if the linkage fails
    ExceptionInInitializerError - if the initialization provoked by this method fails
    ClassNotFoundException - if the class cannot be located
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate forName() method
    public class Test
    {
        public static void main(String[] args)
                             throws ClassNotFoundException
        {
            // forName method
            // it returns the Class object for the class 
            // with the specified name 
            Class c = Class.forName("java.lang.String");
              
            System.out.print("Class represented by c : " + c.toString());
        }
    }

    chevron_right

    
    

    Output:

    Class represented by c : class java.lang.String
    
  3. Class<?> forName(String className,boolean initialize, ClassLoader loader) : This method also returns the Class object associated with the class or interface with the given string name using the given class loader.

    The specified class loader is used to load the class or interface. If the parameter loader is null, the class is loaded through the bootstrap class loader in. The class is initialized only if the initialize parameter is true and if it has not been initialized earlier.

    Syntax : 
    public static Class<?> forName(String className,boolean initialize, ClassLoader loader) 
    throws ClassNotFoundException
    Parameters : 
    className - the fully qualified name of the desired class
    initialize - whether the class must be initialized
    loader - class loader from which the class must be loaded
    Returns :
    return the Class object for the class with the specified name.
    Throws :
    LinkageError : if the linkage fails
    ExceptionInInitializerError - if the initialization provoked by this method fails
    ClassNotFoundException - if the class cannot be located
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate forName() method
    public class Test
    {
        public static void main(String[] args)
                             throws ClassNotFoundException
        {
            // returns the Class object for this class
            Class myClass = Class.forName("Test");
          
            ClassLoader loader = myClass.getClassLoader();
              
            // forName method
            // it returns the Class object for the class 
            // with the specified name using the given class loader
            Class c = Class.forName("java.lang.String",true,loader);
              
            System.out.print("Class represented by c : " + c.toString());
        }
    }

    chevron_right

    
    

    Output:

    Class represented by c : class java.lang.String
    
  4. T newInstance() : This method creates a new instance of the class represented by this Class object. The class is created as if by a new expression with an empty argument list. The class is initialized if it has not already been initialized.
    Syntax : 
    public T newInstance() throws InstantiationException,IllegalAccessException
    TypeParameters : 
    T - The class type whose instance is to be returned
    Parameters : 
    NA
    Returns :
    a newly allocated instance of the class represented by this object.
    Throws :
    IllegalAccessException - if the class or its nullary constructor is not accessible.
    InstantiationException - if this Class represents an abstract class, an interface,
    an array class, a primitive type, or void
    or if the class has no nullary constructor; 
    or if the instantiation fails for some other reason.
    ExceptionInInitializerError - if the initialization provoked by this method fails.
    SecurityException - If a security manager, s, is present
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate newInstance() method
    public class Test
    {
        public static void main(String[] args)
                             throws ClassNotFoundException, InstantiationException,
                             IllegalAccessException
        {
            // returns the Class object for this class
            Class myClass = Class.forName("Test");
              
            // creating new instance of this class
            // newInstance method
            Object obj = myClass.newInstance();
              
            // returns the runtime class of obj
            System.out.println("Class of obj : " + obj.getClass());
        }
    }

    chevron_right

    
    

    Output:

    Class of obj : class Test
    
  5. boolean isInstance(Object obj) : This method determines if the specified Object is assignment-compatible with the object represented by this Class. It is equivalent to instanceof operator in java.
    Syntax : 
    public boolean isInstance(Object obj)
    Parameters : 
    obj - the object to check
    Returns :
    true if obj is an instance of this class else return false
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate isInstance() method
    public class Test
    {
        public static void main(String[] args)
                             throws ClassNotFoundException
        {
            // returns the Class object for the class 
            // with the specified name 
            Class c = Class.forName("java.lang.String");
      
            String s = "GeeksForGeeks";
            int i = 10;
              
              
            // checking for Class instance
            // isInstance method
            boolean b1 = c.isInstance(s);
            boolean b2 = c.isInstance(i);
              
            System.out.println("is s instance of String : " + b1);
            System.out.println("is i instance of String : " + b1);
              
        }
    }

    chevron_right

    
    

    Output:

    is s instance of String : true
    is i instance of String : false
    
  6. boolean isAssignableFrom(Class<?> cls) : This method determines if the class or interface represented by this Class object is either the same as, or is a superclass or superinterface, of the class or interface represented by the specified Class parameter.
    Syntax : 
    public boolean isAssignableFrom(Class<?> cls)
    Parameters : 
    cls - the Class object to be checked
    Returns :
    true if objects of the type cls can be assigned to objects of this class
    Throws:
    NullPointerException - if the specified Class parameter is null.
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate isAssignableFrom() method
    public class Test extends Thread
    {
        public static void main(String[] args)
                             throws ClassNotFoundException, InstantiationException,
                             IllegalAccessException
        {
            // returns the Class object for this class
            Class myClass = Class.forName("Test");
              
            // returns the Class object for the class 
            // with the specified name 
            Class c1 = Class.forName("java.lang.Thread");
            Class c2 = Class.forName("java.lang.String");
              
           // isAssignableFrom method on c1
           // it checks whether Thread class is assignable from Test
           boolean b1 = c1.isAssignableFrom(myClass);
             
           // isAssignableFrom method on c2
           // it checks whether String class is assignable from Test
           boolean b2 = c2.isAssignableFrom(myClass);
             
           System.out.println("is Thread class Assignable from Test : " + b1);
           System.out.println("is String class Assignable from Test : " + b2);
             
        }
    }

    chevron_right

    
    

    Output:

    is Thread class Assignable from Test : true
    is String class Assignable from Test : false
    
  7. boolean isInterface() : This method determines if the specified Class object represents an interface type.
    Syntax : 
    public boolean isInterface()
    Parameters : 
    NA
    Returns :
    return true if and only if this class represents an interface type else return false
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate isInterface() method
    public class Test
    {
        public static void main(String[] args)
                             throws ClassNotFoundException
        {
            // returns the Class object for the class 
            // with the specified name 
            Class c1 = Class.forName("java.lang.String");
            Class c2 = Class.forName("java.lang.Runnable");
              
            // checking for interface type
      
            // isInterface method on c1
            boolean b1 = c1.isInterface();
      
            // is Interface method on c2
            boolean b2 = c2.isInterface();
              
            System.out.println("is java.lang.String an interface : " + b1);
            System.out.println("is java.lang.Runnable an interface : " + b2);
        }
    }

    chevron_right

    
    

    Output:

    is java.lang.String an interface : false
    is java.lang.Runnable an interface : true
    
  8. boolean isPrimitive() : This method determines if the specified Class object represents a primitive type.
    Syntax : 
    public boolean isPrimitive() 
    Parameters : 
    NA
    Returns :
    return true if and only if this class represents a primitive type else return false
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate isPrimitive method
    public class Test
    {
        public static void main(String[] args) 
        {
            // returns the Class object associated with an integer;
            Class c1 = int.class;
              
           // returns the Class object associated with Test class
            Class c2 = Test.class;
             
            // checking for primitive type
      
            // isPrimitive method on c1
            boolean b1 = c1.isPrimitive();
      
            // isPrimitive method on c2
            boolean b2 = c2.isPrimitive();
              
            System.out.println("is "+c1.toString()+" primitive : " + b1);
            System.out.println("is "+c2.toString()+" primitive : " + b2);
        }
    }

    chevron_right

    
    

    Output:



    is int primitive : true
    is class Test primitive : false
    
  9. boolean isArray() : This method determines if the specified Class object represents an array class.
    Syntax : 
    public boolean isArray() 
    Parameters : 
    NA
    Returns :
    return true if and only if this class represents an array type else return false
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate isArray method
    public class Test
    {
        public static void main(String[] args)
        {
            int a[] = new int[2];
              
            // returns the Class object for array class
            Class c1 = a.getClass();
              
            // returns the Class object for Test class
            Class c2 = Test.class;
              
            // checking for array type
      
            // isArray method on c1
            boolean b1 = c1.isArray();
      
            // is Array method on c2
            boolean b2 = c2.isArray();
              
            System.out.println("is "+c1.toString()+" an array : " + b1);
            System.out.println("is "+c2.toString()+" an array : " + b2);
              
        }
    }

    chevron_right

    
    

    Output:

    is class [I an array : true
    is class Test an array : false
    
  10. boolean isAnonymousClass() : This method returns true if and only if the this class is an anonymous class. A anonymous class is a like a local classes except that they do not have a name.
    Syntax : 
    public boolean isAnonymousClass() 
    Parameters : 
    NA
    Returns :
    true if and only if this class is an anonymous class.
    false,otherwise.
    
  11. boolean isLocalClass() : This method returns true if and only if the this class is a local class. A local class is a class that is declared locally within a block of Java code, rather than as a member of a class.
    Syntax : 
    public boolean isLocalClass()
    Parameters : 
    NA
    Returns :
    true if and only if this class is a local class.
    false,otherwise.
    
  12. boolean isMemberClass() : This method returns true if and only if the this class is a Member class.A member class is a class that is declared as a non-static member of a containing class.
    Syntax : 
    public boolean isMemberClass() 
    Parameters : 
    NA
    Returns :
    true if and only if this class is a Member class.
    false,otherwise.
    
  13. Below is the Java program explaining uses of isAnonymousClass() ,isLocalClass and isMemberClass() methods.

    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate isAnonymousClass() ,isLocalClass 
    // and isMemberClass() method
      
    public class Test
    {
        // any Member class of Test
        class A{}
          
        public static void main(String[] args) 
        {
            // declaring an anonymous class
            Test t1 = new Test()
            {
                //  class definition of anonymous class
            };
              
            // returns the Class object associated with t1 object
            Class c1 = t1.getClass();
              
            // returns the Class object associated with Test class
            Class c2 = Test.class;
              
            // returns the Class object associated with A class
            Class c3 = A.class;
              
            // checking for Anonymous class
            // isAnonymousClass method
            boolean b1 = c1.isAnonymousClass();
            System.out.println("is "+c1.toString()+" an anonymous class : "+b1);
                  
            // checking for Local class
            // isLocalClass method
            boolean b2 = c2.isLocalClass();
            System.out.println("is "+c2.toString()+" a local class : " + b2);
              
            // checking for Member class
            // isMemberClass method
            boolean b3 = c3.isMemberClass();
            System.out.println("is "+c3.toString()+" a member class : " + b3);
             
        }
    }

    chevron_right

    
    

    Output:

    is class Test$1 an anonymous class : true
    is class Test a local class : false
    is class Test$A a member class : true
    
  14. boolean isEnum() : This method returns true if and only if this class was declared as an enum in the source code.
    Syntax : 
    public boolean isEnum() 
    Parameters : 
    NA
    Returns :
    true iff this class was declared as an enum in the source code.
    false,otherwise.
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate isEnum() method
      
    enum Color
    {
        RED, GREEN, BLUE;
    }
       
    public class Test
    {
        public static void main(String[] args) 
        {   
            // returns the Class object associated with Color(an enum class)
            Class c1 = Color.class;
              
            // returns the Class object associated with Test class
            Class c2 = Test.class;
              
            // checking for Enum class
            // isEnum method
            boolean b1 = c1.isEnum();
            boolean b2 = c2.isEnum();
              
            System.out.println("is "+c1.toString()+" an Enum class : " + b1);
            System.out.println("is "+c2.toString()+" an Enum class : " + b2);
        }
    }

    chevron_right

    
    

    Output:

    is class Color an Enum class : true
    is class Test an Enum class : false
    
  15. boolean isAnnotation() : This method determines if this Class object represents an annotation type. Note that if this method returns true, isInterface() method will also return true, as all annotation types are also interfaces.
    Syntax : 
    public boolean isAnnotation() 
    Parameters : 
    NA
    Returns :
    return true if and only if this class represents an annotation type else return false
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate isAnnotation() method
      
    // declaring an Annotation Type
    @interface A
    {
         // Annotation element definitions
    }
      
    public class Test
    {
        public static void main(String[] args)
                             throws ClassNotFoundException
        {
            // returns the Class object associated with A  annotation
            Class c1 = A.class;
      
            // returns the Class object associated with Test class
            Class c2 = Test.class;
              
            // checking for annotation type
            // isAnnotation method
            boolean b1 = c1.isAnnotation();
            boolean b2 = c2.isAnnotation();
              
            System.out.println("is "+c1.toString()+" an annotation  : " + b1);
            System.out.println("is "+c2.toString()+" an annotation : " + b2);
              
        }
    }

    chevron_right

    
    

    Output:

    is interface A an annotation  : true
    is class Test an annotation : false
    
  16. String getName() : This method returns the name of the entity (class, interface, array class, primitive type, or void) represented by this Class object, as a String.
    Syntax : 
    public String getName()
    Parameters : 
    NA
    Returns :
    returns the name of the name of the entity 
    represented by this object.
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate getName() method
    public class Test
    {
        public static void main(String[] args) 
        {
            // returns the Class object associated with Test class
            Class c = Test.class;
              
            System.out.print("Class Name associated with c : ");
      
            // returns the name of the class
            // getName method
            System.out.println(c.getName());
        }
    }

    chevron_right

    
    

    Output:

    Class Name associated with c : Test
    
  17. String getSimpleName() : This method returns the name of the underlying class as given in the source code. It returns an empty string if the underlying class is anonymous class.

    The simple name of an array is the simple name of the component type with “[]” appended. In particular the simple name of an array whose component type is anonymous is “[]”.

    Syntax : 
    public String getSimpleName()
    Parameters : 
    NA
    Returns :
    the simple name of the underlying class
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate getSimpleName() method
    public class Test
    {
        public static void main(String[] args) 
                throws ClassNotFoundException 
        {
            // returns the Class object for the class 
            // with the specified name 
            Class c1 = Class.forName("java.lang.String");
      
            System.out.print("Class Name associated with c : ");
              
            // returns the name of the class
            // getName method
            System.out.println(c1.getName());
      
            System.out.print("Simple class Name associated with c : ");
              
            // returns the simple name of the class
            // getSimpleName method
            System.out.println(c1.getSimpleName());
        }
    }

    chevron_right

    
    

    Output:

    Class Name associated with c : java.lang.String
    Simple class Name associated with c : String
    
  18. ClassLoader getClassLoader() : This method returns the class loader for this class. If the class loader is bootstrap classloader then this method returned null, as bootstrap classloader is implemented in native languages like C, C++.
    If this object represents a primitive type or void,then also null is returned.

    Syntax : 
    public ClassLoader getClassLoader()
    Parameters : 
    NA
    Returns :
    the class loader that loaded the class or interface represented by this object
    represented by this object.
    Throws :
    SecurityException - If a security manager and its checkPermission method 
    denies access to the class loader for the class.
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate getClassLoader() method
    public class Test
    {
        public static void main(String[] args)
                             throws ClassNotFoundException
        {
            // returns the Class object for this class
            Class myClass = Class.forName("Test");
              
              
            // returns the Class object for the class 
            // with the specified name 
            Class c1 = Class.forName("java.lang.String");
              
            // returns the Class object for primitive int
            Class c2 = int.class;
              
            System.out.print("Test class loader : ");
              
            // getting the class loader for Test class
            // getClassLoader method on myClass
            System.out.println(myClass.getClassLoader());
              
            System.out.print("String class loader : ");
              
            // getting the class loader for String class
            // we will get null as String class is loaded
            // by BootStrap class loader
            // getClassLoader method on c1
            System.out.println(c1.getClassLoader());     
              
            System.out.print("primitive int loader : ");
              
            // getting the class loader for primitive int
            // getClassLoader method on c2
            System.out.println(c2.getClassLoader());
        }
    }

    chevron_right

    
    

    Output:



    Test class loader : sun.misc.Launcher$AppClassLoader@73d16e93
    String class loader : null
    primitive int loader : null
    
  19. TypeVariable<Class<T>>[ ] getTypeParameters() : This method returns an array of TypeVariable objects that represent the type variables declared by the generic declaration represented by this GenericDeclaration object, in declaration order
    Syntax : 
    public TypeVariable<Class<T>>[] getTypeParameters()
    Specified by:
    getTypeParameters in interface GenericDeclaration
    Parameters : 
    NA
    Returns :
    an array of TypeVariable objects that represent the type variables declared 
    by this generic declaration represented by this object.
    Throws :
    GenericSignatureFormatError - if the generic signature of this generic declaration 
    does not conform to the format specified in JVM.
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate getTypeParameters() method
      
    import java.lang.reflect.TypeVariable;
      
    public class Test
    {
        public static void main(String[] args)
                             throws ClassNotFoundException
        {
            // returns the Class object for the class 
            // with the specified name 
            Class c = Class.forName("java.util.Set");
              
            // getting array of TypeVariable for myClass object
            // getTypeParameters method
            TypeVariable[] tv = c.getTypeParameters();
              
            System.out.println("TypeVariables in "+c.getName()+" class : ");
              
            // iterating through all TypeVariables
            for (TypeVariable typeVariable : tv)
            {
                System.out.println(typeVariable);
            }
              
        }
    }

    chevron_right

    
    

    Output:

    TypeVariables in java.util.Set class : 
    E
    
  20. Class<? super T> getSuperclass() : This method returns the Class representing the superclass of the entity (class, interface, primitive type or void) represented by this Class.
    If this Class represents either the Object class, an interface, a primitive type, or void, then null is returned.
    If this object represents an array class then the Class object representing the Object class is returned.

    Syntax : 
    public Class<? super T> getSuperclass() 
    Parameters : 
    NA
    Returns :
    the superclass of the class represented by this object
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate getSuperclass() method
      
    // base class
    class A
    {
        // methods and fields
    }
      
    // derived class
    class B extends A
    {
          
    }
      
    // Driver class
    public class Test
    {
        public static void main(String[] args) 
                throws ClassNotFoundException 
          
        {
            // returns the Class object associated with Test class
            Class myClass = Test.class;
              
            // returns the Class object for the class 
            // with the specified name 
            Class c1 = Class.forName("A");
            Class c2 = Class.forName("B");
            Class c3 = Class.forName("java.lang.Object");
              
            // getSuperclass method returns the superclass of the class represented 
            // by this class object 
              
            System.out.print("Test superclass : ");
              
            // getSuperclass method on myClass
            System.out.println(myClass.getSuperclass());
              
            System.out.print("A superclass : ");
              
            // getSuperclass method on c1
            System.out.println(c1.getSuperclass());
              
            System.out.print("B superclass : ");
              
            // getSuperclass method on c2
            System.out.println(c2.getSuperclass());
              
            System.out.print("Object superclass : ");
              
            // getSuperclass method on c3
            System.out.println(c3.getSuperclass());
        }
    }

    chevron_right

    
    

    Output:

    Test superclass : class java.lang.Object
    A superclass : class java.lang.Object
    B superclass : class A
    Object superclass : null
    
  21. Type getGenericSuperclass() : This method returns the Type representing the direct superclass of the entity (class, interface, primitive type or void) represented by this Class.

    If this Class represents either the Object class, an interface, a primitive type, or void, then null is returned. If this object represents an array class then the Class object representing the Object class is returned.

    Syntax : 
    public Type getGenericSuperclass()
    Parameters : 
    NA
    Returns :
    the superclass of the class represented by this object
    Throws:
    GenericSignatureFormatError - if the generic class signature does not conform to the format 
    specified in JVM
    TypeNotPresentException - if the generic superclass refers to a non-existent 
    type declaration MalformedParameterizedTypeException - if the generic 
    superclass refers to a parameterized type
    that cannot be instantiated for any reason
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate 
    // getGenericSuperclass() method
    public class Test
    {
        public static void main(String[] args) 
                throws ClassNotFoundException 
          
        {
            // returns the Class object associated with Test class
            Class myClass = Test.class;
              
            // returns the Class object for the class 
            // with the specified name 
            Class c1 = Class.forName("java.util.ArrayList");
            Class c3 = Class.forName("java.lang.Object");
              
            // getGenericSuperclass method returns the generic 
            // superclass of the class represented 
            // by this class object 
              
            System.out.print("Test superclass : ");
              
            // getGenericSuperclass method on myClass
            System.out.println(myClass.getGenericSuperclass());
              
            System.out.print("ArrayList superclass : ");
              
            // getGenericSuperclass method on c1
            System.out.println(c1.getGenericSuperclass());
              
            System.out.print("Object superclass : ");
              
            // getGenericSuperclass method on c3
            System.out.println(c3.getGenericSuperclass());
        }
    }

    chevron_right

    
    

    Output:

    Test superclass : class java.lang.Object
    Set superclass : java.util.AbstractList<E>
    Object superclass : null
    
  22. Class<?>[] getInterfaces() : This method returns the interfaces implemented by the class or interface represented by this object.

    If this object represents a class or interface that implements no interfaces, the method returns an array of length 0.
    If this object represents a primitive type or void, the method returns an array of length 0.

    Syntax : 
    public Class<?>[] getInterfaces()
    Parameters : 
    NA
    Returns :
    an array of interfaces implemented by this class.
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate getInterfaces() method
      
    // base interface
    interface A
    {
        // methods and constant declarations
    }
      
    // derived class
    class B implements A
    {
        // methods implementations that were declared in A
    }
      
    // Driver class
    public class Test
    {
        public static void main(String[] args) 
                throws ClassNotFoundException 
          
        {
            // returns the Class object for the class 
            // with the specified name 
            Class c1 = Class.forName("B");
            Class c2 = Class.forName("java.lang.String");
              
            // getInterface method on c1
            // it returns the interfaces implemented by B class
            Class c1Interfaces[] = c1.getInterfaces();
              
            // getInterface method on c2
            // returns the interfaces implemented by String class
            Class c2Interfaces[] = c2.getInterfaces();
              
              
            System.out.println("interfaces implemented by B class : ");
              
            // iterating through B class interfaces
            for (Class class1 : c1Interfaces) 
            {
                System.out.println(class1);
            }
              
              
            System.out.println("interfaces implemented by String class : ");
              
            // iterating through String class interfaces
            for (Class class1 : c2Interfaces) 
            {
                System.out.println(class1);
            }
        }
    }

    chevron_right

    
    

    Output:

    interfaces implemented by B class : 
    interface A
    interfaces implemented by String class : 
    interface java.io.Serializable
    interface java.lang.Comparable
    interface java.lang.CharSequence
    
  23. Type[] getGenericInterfaces() : This method returns the Types representing the interfaces directly implemented by the class or interface represented by this object.

    If this object represents a class or interface that implements no interfaces, the method returns an array of length 0.
    If this object represents a primitive type or void, the method returns an array of length 0.

    Syntax : 
    public Type[] getGenericInterfaces()
    Parameters : 
    NA
    Returns :
    an array of interfaces implemented by this class
    Throws:
    GenericSignatureFormatError - if the generic class signature does not conform to the format 
    specified in JVM
    TypeNotPresentException - if the generic superinterfaces refers to 
    a non-existent type declaration MalformedParameterizedTypeException - if the
    generic superinterfaces refers to a parameterized type
    that cannot be instantiated for any reason
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate getGenericInterfaces() method
      
    import java.lang.reflect.Type;
      
    public class Test
    {
        public static void main(String[] args) 
                throws ClassNotFoundException 
          
        {
            // returns the Class object for the class 
            // with the specified name 
            Class c1 = Class.forName("java.util.Set");
              
            // getGenericInterfaces() on c1
            // it returns the interfaces implemented by Set interface
            Type c1GenericInterfaces[] = c1.getGenericInterfaces();
              
            System.out.println("interfaces implemented by Set interface : ");
              
            // iterating through Set class interfaces
            for (Type type : c1GenericInterfaces)
            {
                System.out.println(type);
            }
        }
    }

    chevron_right

    
    

    Output:

    interfaces implemented by Set interface : 
    java.util.Collection<E>
    
  24. Package getPackage() : This method returns the package for this class. The classloader subsystem in JVM Architecture used this method to find the package of a class or interface.
    Syntax : 
    public Package getPackage()
    Parameters : 
    NA
    Returns :
    the package of the class, 
    or null if no package information is available
    from the archive or codebase. 
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate getPackage() method
    public class Test
    {
        public static void main(String[] args) throws ClassNotFoundException
        {
            // returns the Class object for the class 
            // with the specified name 
            Class c1 = Class.forName("java.lang.String");
            Class c2 = Class.forName("java.util.ArrayList");
              
            // getting package of class
      
            // getPackage method on c1
            System.out.println(c1.getPackage());
      
            // getPackage method on c2
            System.out.println(c2.getPackage());
      
        }
    }

    chevron_right

    
    

    Output:



    package java.lang, Java Platform API Specification, version 1.8
    package java.util, Java Platform API Specification, version 1.8
    
  25. Field[] getFields() : This method returns an array of Field objects reflecting all the accessible public fields of the class(and of all its superclasses) or interface(and of all its superclasses) represented by this Class object.
    Syntax : 
    public Field[] getFields()  throws SecurityException
    Parameters : 
    NA
    Returns :
    the array of Field objects representing the public fields
    and  array of length 0 if the class or interface has no accessible public fields
    or if this Class object represents a primitive type or void.
    Throws :
    SecurityException - If a security manager, s, is present.
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate getFields() method
      
    import java.lang.reflect.Field;
      
    public class Test
    {
        public static void main(String[] args) 
                throws SecurityException,ClassNotFoundException
        {
            // returns the Class object for the class 
            // with the specified name 
            Class c1 = Class.forName("java.lang.Integer");
              
            // getFields method on c1
            // it array of fields of Integer class
            Field F[] = c1.getFields();
              
            System.out.println("Below are the fields of Integer class : ");
              
            // iterating through all fields of  String class
            for (Field field : F) 
            {
                    System.out.println(field);
            
        }
    }

    chevron_right

    
    

    Output :

    Below are the fields of Integer class :
    public static final int java.lang.Integer.MIN_VALUE
    public static final int java.lang.Integer.MAX_VALUE
    public static final java.lang.Class java.lang.Integer.TYPE
    public static final int java.lang.Integer.SIZE
    public static final int java.lang.Integer.BYTES
    
  26. Class<?>[ ] getClasses() : This method returns an array containing Class objects representing all the public classes and interfaces that are members of the class represented by this Class object. The array contains public class and interface members inherited from superclasses and public class and interface members declared by the class.

    This method returns an array of length 0 if this Class object has no public member classes or interfaces.
    This method also returns an array of length 0 if this Class object represents a primitive type, an array class, or void.

    Syntax : 
    Class<?>[ ] getClasses()
    Parameters : 
    NA
    Returns :
    the array of Class objects representing the public members of this class
    Throws :
    SecurityException - If a security manager, s, is present.
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate getClasses() method
      
    public class Test
    {
        // base interface
        public interface A
        {
            // methods and constant declarations
        }
      
        // derived class
        public class B implements A
        {
            // methods implementations that were declared in A
        }
          
        public static void main(String[] args) 
                throws ClassNotFoundException 
          
        {
            // returns the Class object associated with Test class
            Class c1 = Test.class;
              
            // getClasses method on c1
            // it returns the array of Class objects containing the all 
            // public classes and interfaces  represented by Test class
            Class[] c1Classes = c1.getClasses();
              
            System.out.println("public members of Test class : ");
              
            // iterating through all public members of Test class
            for (Class class1 : c1Classes)
            {
                System.out.println(class1);
            }
              
        }
    }

    chevron_right

    
    

    Output:

    public members of Test class : 
    interface Test$A
    class Test$B
    
  27. Method[] getMethods() : This method returns an array of Method objects reflecting all the accessible public methods of the class or interface and those inherited from superclasses and super interfaces represented by this Class object.
    Syntax : 
    public Method[] getMethods() throws SecurityException
    Parameters : 
    NA
    Returns :
    the array of Method objects representing the public methods
    and  array of length 0 if the class or interface has no accessible public method
    or if this Class object represents a primitive type or void.
    Throws :
    SecurityException - If a security manager, s, is present.
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate getMethods() method
      
    import java.lang.reflect.Method;
      
    public class Test
    {
        public static void main(String[] args) 
                throws SecurityException,ClassNotFoundException
        {
            // returns the Class object for the class 
            // with the specified name 
            Class c1 = Class.forName("java.lang.Object");
              
            // getMethods method on c1
            // it returns array of methods of Object class
            Method M[] = c1.getMethods();
              
            System.out.println("Below are the methods of Object class : ");
              
            // iterating through all methods of Object class
            for (Method method : M) 
            {
            System.out.println(method);
            }
        }
    }

    chevron_right

    
    

    Output:

    Below are the methods of Object class : 
    public final void java.lang.Object.wait() throws java.lang.InterruptedException
    public final void java.lang.Object.wait(long,int) throws java.lang.InterruptedException
    public final native void java.lang.Object.wait(long) throws java.lang.InterruptedException
    public boolean java.lang.Object.equals(java.lang.Object)
    public java.lang.String java.lang.Object.toString()
    public native int java.lang.Object.hashCode()
    public final native java.lang.Class java.lang.Object.getClass()
    public final native void java.lang.Object.notify()
    public final native void java.lang.Object.notifyAll()
    
  28. Constructor<?>[] getConstructors() : This method returns an array of Constructor objects reflecting all the public constructors of the class represented by this Class object.
    Syntax : 
    public Constructor<?>[] getConstructors() throws SecurityException
    Parameters : 
    NA
    Returns :
    the array of Constructor objects representing the public constructors of this class
    and  array of length 0 if the class or interface has no accessible public constructor
    or if this Class object represents a primitive type or void.
    Throws :
    SecurityException - If a security manager, s, is present.
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate getConstructors() method
      
    import java.lang.reflect.Constructor;
      
    public class Test
    {
        public static void main(String[] args) 
                throws SecurityException,ClassNotFoundException
        {
            // returns the Class object for the class 
            // with the specified name 
            Class c1 = Class.forName("java.lang.Boolean");
              
            // getConstructor method on c1
            // it returns an array of constructors of Boolean class
            Constructor C[] = c1.getConstructors();
              
            System.out.println("Below are the constructors of Boolean class :");
              
            // iterating through all constructors
            for (Constructor constructor : C) 
            {
            System.out.println(constructor);
            }
        }
    }

    chevron_right

    
    

    Output:

    Below are the constructors of Boolean class :
    public java.lang.Boolean(boolean)
    public java.lang.Boolean(java.lang.String)
    
  29. Field getField(String fieldName) : This method returns a Field object that reflects the specified public member field of the class or interface represented by this Class object.
    Syntax : 
    public Field getField(String fieldName) throws NoSuchFieldException,SecurityException
    Parameters : 
    fieldName -  the field name
    Returns :
    the Field object of this class specified by name
    Throws :
    NoSuchFieldException - if a field with the specified name is not found.
    NullPointerException - if fieldName is null
    SecurityException - If a security manager, s, is present.
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate getField() method
      
    import java.lang.reflect.Field;
      
    public class Test
    {
        public static void main(String[] args) 
                throws SecurityException,ClassNotFoundException,
                       NoSuchFieldException
        {
            // returns the Class object for the class 
            // with the specified name 
            Class c1 = Class.forName("java.lang.Integer");
              
            // getField method on c1
            // it checks a public field in Integer class with specified parameter
            Field f = c1.getField("MIN_VALUE");
              
            System.out.println("public field in Integer class with MIN_VALUE name :");
            System.out.println(f);
        }
    }

    chevron_right

    
    

    Output:

    public field in Integer class with MIN_VALUE name :
    public static final int java.lang.Integer.MIN_VALUE
    
  30. Method getMethod(String methodName,Class… parameterTypes) : This method returns a Method object that reflects the specified public member method of the class or interface represented by this Class object.
    Syntax : 
    public Method getMethod(String methodName,Class... parameterTypes) throws 
    NoSuchFieldException,SecurityException
    Parameters : 
    methodName -  the method name
    parameterTypes - the list of parameters
    Returns :
    the method object of this class specified by name
    Throws :
    NoSuchMethodException - if a method with the specified name is not found.
    NullPointerException - if methodName is null
    SecurityException - If a security manager, s, is present.
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate getMethod() method
      
    import java.lang.reflect.Method;
      
    public class Test
    {
        public static void main(String[] args) 
                throws SecurityException,ClassNotFoundException,
                       NoSuchMethodException
        {
            // returns the Class object for the class 
            // with the specified name 
            Class c1 = Class.forName("java.lang.Integer");
            Class c2 = Class.forName("java.lang.String");
              
            // getMethod method on c1
            // it checks for a public Method in Integer class
            Method m = c1.getMethod("parseInt",c2);
              
            System.out.println("method in Integer class specified by parseInt : ");
            System.out.println(m);
        }
    }

    chevron_right

    
    

    Output:

    public method in Integer class specified by parseInt : 
    public static int java.lang.Integer.parseInt(java.lang.String) 
    throws java.lang.NumberFormatException
    
  31. Constructor<?> getConstructor(Class<?>… parameterTypes) : This method returns a Constructor object that reflects the specified public constructor of the class represented by this Class object.The parameterTypes parameter is an array of Class objects that identify the constructor’s formal parameter types, in declared order.
    Syntax : 
    public Constructor<?> getConstructor(Class<?>... parameterTypes) 
    throws NoSuchMethodException,SecurityException
    Parameters : 
    parameterTypes - the list of parameters
    Returns :
    the Constructor object of the public constructor that matches the specified parameterTypes
    Throws :
    NoSuchMethodException - if a Constructor with the specified parameterTypes is not found.
    SecurityException - If a security manager, s, is present.
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate 
    // getConstructor() Constructor
      
    import java.lang.reflect.Constructor;
      
    public class Test
    {
        public static void main(String[] args) 
                throws SecurityException,ClassNotFoundException,
                    NoSuchMethodException
        {
            // returns the Class object for the class 
            // with the specified name 
            Class c1 = Class.forName("java.lang.Integer");
            Class c2 = Class.forName("java.lang.String");
              
            // getConstructor method on c1
            // it checks a public Constructor in Integer class
            // with specified parameterTypes
            Constructor c = c1.getConstructor(c2);
              
            System.out.println("Constructor in Integer class & String parameterType:");
            System.out.println(c);
        }
    }

    chevron_right

    
    

    Output:

    public Constructor in Integer class with String parameterType : 
    public java.lang.Integer(java.lang.String) throws java.lang.NumberFormatException
    
  32. Note : The methods getFields(), getMethods(),getConstructors(), getField(), getMethod(), getConstructor() are widely used in Reflection(Refer this for example)

  33. T cast(Object obj) : This method is used to casts an object to the class or interface represented by this Class object.
    Syntax : 
    public T cast(Object obj)
    TypeParameters : 
    T - The class type whose object is to be cast
    Parameters : 
    obj - the object to be cast
    Returns :
    the object after casting, or null if obj is null
    Throws :
    ClassCastException - if the object is not null and is not assignable to the type T. 
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate cast() method
    class A
    {
       // methods and fields
    }
      
    class B extends
    {
        // methods and fields
    }
      
    // Driver Class
    public class Test
    {
        public static void main(String[] args) 
        {
            A a = new A();   
              
            System.out.println(a.getClass());
              
            B b = new B();
              
            // casting b to a
            // cast method
            a = A.class.cast(b);
         
            System.out.println(a.getClass());
          
        }
    }

    chevron_right

    
    

    Output:

    class A
    class B
    
  34. <U> Class<? extends U> asSubclass(Class<U> clazz) : This method is used to cast this Class object to represent a subclass of the class represented by the specified class object.It always returns a reference to this class object.
    Syntax : 
    public <U> Class<? extends U> asSubclass(Class<U> class)
    TypeParameters : 
    U - The superclass type whose object is to be cast
    Parameters : 
    clazz - the superclass object to be cast
    Returns :
    this Class object, cast to represent a subclass of the specified class object.
    Throws :
    ClassCastException - if this Class object does not represent a 
    subclass of the specified class
    (here "subclass" includes the class itself).
    
    filter_none

    edit
    close

    play_arrow

    link
    brightness_4
    code

    // Java program to demonstrate asSubclass() method
    class A
    {
       // methods and fields
    }
      
    class B extends
    {
        // methods and fields
    }
      
    // Driver Class
    public class Test
    {
        public static void main(String[] args) 
        {
            A a = new A();   
              
            // returns the Class object for super class(A)
            Class superClass = a.getClass();
              
            B b = new B();
              
            // returns the Class object for subclass(B)
            Class subClass = b.getClass();
              
            // asSubclass method
            // it represent a subclass of the specified  class object
            Class cast = subClass.asSubclass(superClass);
              
            System.out.println(cast);
          
        }
    }

    chevron_right

    
    

    Output:

    class B
    
  35. This article is contributed by Gaurav Miglani. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

    Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.



    My Personal Notes arrow_drop_up


    Article Tags :
    Practice Tags :


    1


    Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.