Built-in Exceptions in Java with examples

Types of Exceptions in Java

Built-in exceptions are the exceptions which are available in Java libraries. These exceptions are suitable to explain certain error situations. Below is the list of important built-in exceptions in Java.
Examples of Built-in Exception:

1. Arithmetic exception : It is thrown when an exceptional condition has occurred in an arithmetic operation.

   // Java program to demonstrate
   // ArithmeticException
   class ArithmeticException_Demo {
   public static void main(String args[])
       {
           try {
               int a = 30, b = 0;
               int c = a / b; // cannot divide by zero
               System.out.println("Result = " + c);
           }
           catch (ArithmeticException e) {
               System.out.println("Can't divide a number by 0");
           }
       }
   }

   Output:

   Can't divide a number by 0
   

2. ArrayIndexOutOfBounds Exception : It is thrown to indicate that an array has been accessed with an illegal index. The index is either negative or greater than or equal to the size of the array.

   // Java program to demonstrate
   // ArrayIndexOutOfBoundException
   class ArrayIndexOutOfBound_Demo {
   public static void main(String args[])
       {
           try {
               int a[] = new int[5];
               a[6] = 9; // accessing 7th element in an array of
               // size 5
           }
           catch (ArrayIndexOutOfBoundsException e) {
               System.out.println("Array Index is Out Of Bounds");
           }
       }
   }

   Output:
   

   Array Index is Out Of Bounds

3. ClassNotFoundException : This Exception is raised when we try to access a class whose definition is not found.

   // Java program to illustrate the
   // concept of ClassNotFoundException
   class Bishal {
   
   } class Geeks {
   
   } class MyClass {
   public static void main(String[] args)
       {
           Object o = class.forName(args[0]).newInstance();
           System.out.println("Class created for" + o.getClass().getName());
       }
   }

   Output:

   ClassNotFoundException

4. FileNotFoundException : This Exception is raised when a file is not accessible or does not open.

   // Java program to demonstrate
   // FileNotFoundException
   import java.io.File;
   import java.io.FileNotFoundException;
   import java.io.FileReader;
   class File_notFound_Demo {
   
   public static void main(String args[])
       {
           try {
   
               // Following file does not exist
               File file = new File("E:// file.txt");
   
               FileReader fr = new FileReader(file);
           }
           catch (FileNotFoundException e) {
               System.out.println("File does not exist");
           }
       }
   }

   Output:

   File does not exist

5. IOException : It is thrown when an input-output operation failed or interrupted

   // Java program to illustrate IOException
   import java.io.*;
   class Geeks {
   public static void main(String args[])
       {
           FileInputStream f = null;
           f = new FileInputStream("abc.txt");
           int i;
           while ((i = f.read()) != -1) {
               System.out.print((char)i);
           }
           f.close();
       }
   }

   Output:

   error: unreported exception IOException; must be caught or declared to be thrown
   

6. InterruptedException : It is thrown when a thread is waiting, sleeping, or doing some processing, and it is interrupted.

   // Java Program to illustrate
   // InterruptedException
   class Geeks {
   public static void main(String args[])
       {
           Thread t = new Thread();
           t.sleep(10000);
       }
   }

   Output:

   error: unreported exception InterruptedException; must be caught or declared to be thrown
   

7. NoSuchMethodException : t is thrown when accessing a method which is not found.

   // Java Program to illustrate
   // NoSuchMethodException
   class Geeks {
   public Geeks()
       {
           Class i;
           try {
               i = Class.forName("java.lang.String");
               try {
                   Class[] p = new Class[5];
               }
               catch (SecurityException e) {
                   e.printStackTrace();
               }
               catch (NoSuchMethodException e) {
                   e.printStackTrace();
               }
           }
           catch (ClassNotFoundException e) {
               e.printStackTrace();
           }
       }
   
   public static void main(String[] args)
       {
           new Geeks();
       }
   }

   Output:

   error: exception NoSuchMethodException is never thrown 
   in body of corresponding try statement
   

8. NullPointerException : This exception is raised when referring to the members of a null object. Null represents nothing

   // Java program to demonstrate NullPointerException
   class NullPointer_Demo {
   public static void main(String args[])
       {
           try {
               String a = null; // null value
               System.out.println(a.charAt(0));
           }
           catch (NullPointerException e) {
               System.out.println("NullPointerException..");
           }
       }
   }

   Output:

   NullPointerException..
   

9. NumberFormatException : This exception is raised when a method could not convert a string into a numeric format.

   // Java program to demonstrate
   // NumberFormatException
   class NumberFormat_Demo {
   public static void main(String args[])
       {
           try {
               // "akki" is not a number
               int num = Integer.parseInt("akki");
   
               System.out.println(num);
           }
           catch (NumberFormatException e) {
               System.out.println("Number format exception");
           }
       }
   }

   Output:

   Number format exception
   

10. StringIndexOutOfBoundsException : It is thrown by String class methods to indicate that an index is either negative than the size of the string.

    // Java program to demonstrate
    // StringIndexOutOfBoundsException
    class StringIndexOutOfBound_Demo {
    public static void main(String args[])
        {
            try {
                String a = "This is like chipping "; // length is 22
                char c = a.charAt(24); // accessing 25th element
                System.out.println(c);
            }
            catch (StringIndexOutOfBoundsException e) {
                System.out.println("StringIndexOutOfBoundsException");
            }
        }
    }

    Output:

    StringIndexOutOfBoundsException
    

Some other important Exceptions

1. ClassCastException

   // Java Program to illustrate
   // ClassCastException
   class Test {
   public static void main(String[] args)
       {
           String s = new String("Geeks");
           Object o = (Object)s;
           Object o1 = new Object();
           String s1 = (String)o1;
       }
   }

   Output:

   Exception in thread "main" java.lang.ClassCastException: 
   java.lang.Object cannot be cast to java.lang.String
   

2. StackOverflowError

   // Java Program to illustrate
   // StackOverflowError
   class Test {
   public static void main(String[] args)
       {
           m1();
       }
   public static void m1()
       {
           m2();
       }
   public static void m2()
       {
           m1();
       }
   }

   Output:

   Exception in thread "main" java.lang.StackOverflowError
   

3. NoClassDefFoundError

   // Java Program to illustrate
   // NoClassDefFoundError
   class Test //
       {
   public static void main(String[] args)
       {
           System.out.println("HELLO GEEKS");
       }
   }

   Output:

   Note: If the corresponding Test.class file is not found 
   during compilation then we will get Run-time Exception
   saying Exception in thread "main" java.lang.NoClassDefFoundError
   

4. ExceptionInInitializerError
   Code 1:

   // Java Program to illustrate
   // ExceptionInInitializerError
   class Test {
       static int x = 10 / 0;
   public static void main(String[] args)
       {
       }
   }

   Output:

   Exception in thread "main" java.lang.ExceptionInInitializerError
   Caused by: java.lang.ArithmeticException: / by zero
   

   Code 2 :

   // Java Program to illustrate
   // ExceptionInInitializerError
   class Test {
       static
       {
           String s = null;
           System.out.println(s.length());
       }
   public static void main(String[] args)
       {
       }
   }

   Output:

   Exception in thread "main" java.lang.ExceptionInInitializerError
   Caused by: java.lang.NullPointerException
   

   Explanation : The above exception occurs whenever while executing static variable assignment and static block if any Exception occurs.

5. IllegalArgumentException

   // Java Program to illustrate
   // IllegalArgumentException
   class Test {
   public static void main(String[] args)
       {
           Thread t = new Thread();
           Thread t1 = new Thread();
           t.setPriority(7); // Correct
           t1.setPriority(17); // Exception
       }
   }

   Output:

   Exception in thread "main" java.lang.IllegalArgumentException
   

   Explanation:The Exception occurs explicitly either by the programmer or by API developer to indicate that a method has been invoked with Illegal Argument.

6. IllegalThreadStateException

   // Java Program to illustrate
   // IllegalStateException
   class Test {
   public static void main(String[] args)
       {
           Thread t = new Thread();
           t.start();
           t.start();
       }
   }

   Output:

   Exception in thread "main" java.lang.IllegalThreadStateException
   

   Explanation : The above exception rises explicitly either by programmer or by API developer to indicate that a method has been invoked at wrong time.

7. AssertionError

   // Java Program to illustrate
   // AssertionError
   class Test {
   public static void main(String[] args)
       {
           // If x is not greater than or equal to 10
           // then we will get the run-time exception
           assert(x >= 10);
       }
   }

   Output:

   Exception in thread "main" java.lang.AssertionError
   

   Explanation : The above exception rises explicitly by the programmer or by API developer to indicate that assert statement fails.

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