Java Program to Check if a Given Class is a Local Inner Class

Last Updated : 17 Nov, 2020

Local Inner Classes are classes declared inside a block. These classes are only visible inside the block. So, You need to instantiate the class within the block. Sometimes, this block can be for loop or if-else clause. These classes can access the fields of a class enclosing it. The local inner class must be instantiated in the block they are defined in.

We will discuss using the below approaches how to check if a given class is a Local Inner Class.

Approach 1:

To check whether the class is a local inner class, java.lang.Class provides a method called isLocalClass().
This method returns true if the given class is a local class and false otherwise. Note that “isLocalClass()” is defined in java.lang.Class class. So, you need to first call the “getClass()” method of the object.
This method returns the Class instance representing the class of the object. See the following code —

Java

// Java program to check if a class is inner
// local class using isLocalClass() method
  
import java.io.*;
  
class GFG {
    public static void main(String[] args)
    {
        class LocalInnerClass {
            // This is a local inner class
        }
        // Creating a LocalInnerClass object
        LocalInnerClass inner = new LocalInnerClass();
  
        // Getting the Class instance associated with
        // the class of inner(i.e. LocalInnerClass)
        // which is returned by getClass() method of inner
        Class localClass = inner.getClass();
  
        // isLocalClass() method of localClass returns true
        // if and only if localClass is a Local Class
        System.out.println(
            "Is inner a local class object? :"
            + localClass.isLocalClass());
    }
}

Output

Is inner a local class object? :true

Approach 2:

This approach is about checking the canonical name of the class and then deciding whether it is a local class or not.
The getCanonicalName() method defined in java.lang.
Class class, returns the canonical name of the class in as a string.
For example, if the name of a class represented by the java.lang.Class object, is “GFG”, then the “getCanonicalName()” method returns “GFG”.

GFG gfg = new GFG();
System.out.println(gfg.getClass().getCanonicalName());

If we run the above code in a program, then the output received will be:

Output :

GFG

Note: A.) If there is a package name, then the output will be “package-name.GFG”.

But this is not the case for local, anonymous classes.
If the class is a member class, say, “GFG” is a member class of “GeeksForGeeks”, then “getCanonicalName()” will return “GeeksForGeeks.GFG”(in the form “(Name_of_Enclosing_Class).(Name_of_this_Class)”).

Java

// Java program to check what the method returns
// when class is an annymous class
  
import java.io.*;
  
class GeeksForGeeks {
    public static void main(String[] args)
    {
        // Creating a GeeksForGeeks object
        // to create a GFG object
        GeeksForGeeks geeks = new GeeksForGeeks();
        // Creating a GFG object
        GFG gfg = geeks.new GFG();
  
        // getClass() returns a java.lang.Class
        // instance representing the GFG class
        System.out.println(
            gfg.getClass().getCanonicalName());
    }
  
    class GFG {
        // This is a member class of GeeksForGeeks
    }
}

Output

GeeksForGeeks.GFG

B.) If the class is an anonymous class inside a class (say, “GFG”) then the “getCanonicalName()” method returns null because it does not have a canonical name.

Java

// java program to check what the method returns
// when class is an annymous class
  
import java.io.*;
  
class GFG {
    public static void main(String[] args)
    {
        GFG gfg = new GFG() {
            // This is an Anonymous class
            // that extends the GFG class
        }; // Remember to put the semicolon here
        System.out.println(
            gfg.getClass().getCanonicalName());
    }
}

Output

null

C.) If the class is a local inner class, suppose, “GFG” is a local class inside “GeeksForGeeks”, then also “getCanonicalName()” will return null. Because, it does not have a canonical name

Java

// Java program to check if a class is a
// local inner class
  
import java.io.*;
  
class GeeksForGeeks {
    public static void main(String[] args)
    {
        class GFG {
            // This is a local class
        }
        class Geeks {
            // This is an another local class
        }
  
        GFG gfg = new GFG();
        Geeks geeks = new Geeks();
  
        System.out.println(
            "Canonical Name of the class of gfg:"
            + gfg.getClass().getCanonicalName());
        System.out.println(
            "Canonical Name of the class of geeks:"
            + geeks.getClass().getCanonicalName());
    }
}

Output

Canonical Name of the class of gfg:null
Canonical Name of the class of geeks:null

Using this canonical name, you can achieve the given task. Check the following code:

Java

// Java program to check if the class
// local inner class
  
import java.io.*;
  
class GeeksForGeeks {
    public static void main(String[] args)
    {
        class GFG {
            // This is a local class
        }
  
        GFG gfg = new GFG();
  
        // Storing the class instance associated with gfg
        // i.e. Class instance representing GFG
        Class classInstance = gfg.getClass();
  
        // Checking whether the classInstance has a
        // canonical name
        boolean hasCanonicalName
            = (classInstance.getCanonicalName() != null);
  
        // If hasCanonicalName is false then it is sure that
        // either it is a local class or anonymous class or
        // an array whose component type does not have a
        // canonical name
  
        // Now check whether it is an anonymous Class
        boolean isAnonymousClass
            = classInstance.isAnonymousClass();
  
        // Check if it is an array
        boolean isArray = classInstance.isArray();
  
        // If all the three isArray,isAnonymousClass and
        // hasCanonicalName are false then the classInstance
        // is surely a local class
        boolean isLocalClass
            = (!hasCanonicalName && !isAnonymousClass
               && !isArray);
        System.out.println(
            "Is gfg a local class instance?: "
            + isLocalClass);
    }
}

Output

Is gfg a local class instance?: true

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