Java Class cast() Method

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Description

The Java Class cast() method casts an object to the class or interface represented by this Class object.

Declaration

Following is the declaration for java.lang.Class.cast() method

public T cast(Object obj)

Parameters

obj − This is the object to be cast.

Return Value

This method returns the object after casting, or null if obj is null.

Exception

ClassCastException − if the object is not null and is not assignable to the type T.

Casting an Object to a Class Example

The following example shows the usage of java.lang.Class.cast() method. In this program, we've created an instance of ClassDemo and then using getClass() method, the class of the instance is retrieved and is printed. We've two classes A and B where B extends A. Now instance of A and B are created and then using cast() method, instance of B is cast to A.

package com.tutorialspoint;

class A {
   public static void show() {
      System.out.println("Class A show() function");
   }
}

class B extends A {
   public static void show() {
      System.out.println("Class B show() function");
   }
}

public class ClassDemo {

   public static void main(String[] args) {

      ClassDemo cls = new ClassDemo();
      Class c = cls.getClass();      
      System.out.println(c);  

      Object obj = new A();        
      B b1 = new B();
      b1.show();

      // casts object
      Object a = A.class.cast(b1);

      System.out.println(obj.getClass());
      System.out.println(b1.getClass());
      System.out.println(a.getClass());               
   }
} 

Output

Let us compile and run the above program, this will produce the following result −

class com.tutorialspoint.ClassDemo
Class B show() function
class com.tutorialspoint.A
class com.tutorialspoint.B
class com.tutorialspoint.B

Facing Exceptio while Casting an Object to a Class Example

The following example shows the usage of java.lang.Class.cast() method. In this program, we've created an instance of ClassDemo and then using getClass() method, the class of the instance is retrieved and is printed. We've two classes A and B. Now instance of A and B are created and then using cast() method, instance of B is cast to A. As B is not compatible to A, an exception is raised.

package com.tutorialspoint;

class A {
   public static void show() {
      System.out.println("Class A show() function");
   }
}

class B {
   public static void show() {
      System.out.println("Class B show() function");
   }
}

public class ClassDemo {

   public static void main(String[] args) {

      ClassDemo cls = new ClassDemo();
      Class c = cls.getClass();      
      System.out.println(c);  

      Object obj = new A();        
      B b1 = new B();
      b1.show();

      // casts object
      Object a = A.class.cast(b1);

      System.out.println(obj.getClass());
      System.out.println(b1.getClass());
      System.out.println(a.getClass());               
   }
} 

Output

Let us compile and run the above program, this will produce the following result −

class com.tutorialspoint.ClassDemo
Class B show() function
Exception in thread "main" java.lang.ClassCastException: Cannot cast com.tutorialspoint.B to com.tutorialspoint.A
	at java.base/java.lang.Class.cast(Class.java:4067)
	at com.tutorialspoint.ClassDemo.main(ClassDemo.java:28)