Using instanceof

Java provides the run-time operator instanceof to check class type for an object. The instanceof operator has this general form:


object instanceof type

The following program demonstrates instanceof:

 
class A {
}

class B {
}

class C extends A {
}

class D extends A {
}

public class Main{
  public static void main(String args[]) {
    A a = new A();
    B b = new B();
    C c = new C();
    D d = new D();

    if (a instanceof A)
      System.out.println("a is instance of A");
    if (b instanceof B)
      System.out.println("b is instance of B");
    if (c instanceof C)
      System.out.println("c is instance of C");
    if (c instanceof A)
      System.out.println("c can be cast to A");

    if (a instanceof C)
      System.out.println("a can be cast to C");

    A ob;
    ob = d; // A reference to d
    System.out.println("ob now refers to d");
    if (ob instanceof D)
      System.out.println("ob is instance of D");

    ob = c; // A reference to c
    System.out.println("ob now refers to c");
    if (ob instanceof D)
      System.out.println("ob can be cast to D");
    else
      System.out.println("ob cannot be cast to D");

    if (ob instanceof A)
      System.out.println("ob can be cast to A");
    // all objects can be cast to Object
    if (a instanceof Object)
      System.out.println("a may be cast to Object");
    if (b instanceof Object)
      System.out.println("b may be cast to Object");
    if (c instanceof Object)
      System.out.println("c may be cast to Object");
    if (d instanceof Object)
      System.out.println("d may be cast to Object");
  }
}

The output from this program is shown here:


a is instance of A
b is instance of B
c is instance of C
c can be cast to A
ob now refers to d
ob is instance of D
ob now refers to c
ob cannot be cast to D
ob can be cast to A
a may be cast to Object
b may be cast to Object
c may be cast to Object
d may be cast to Object
java2s.com  |  | Contact Us | Privacy Policy
Copyright 2009 - 12 Demo Source and Support. All rights reserved.
All other trademarks are property of their respective owners.