instanceof operator and class hierarchy : instanceof « Operators « Java Tutorial

1. Java Tutorial
2. Operators
3. instanceof

class A {
  int i, j;
}

class B {
  int i, j;
}

class C extends A {
  int k;
}

class D extends A {
  int k;
}

class InstanceOf {
  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");

    System.out.println();

    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");

    System.out.println();

    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");

    System.out.println();

    // 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");
  }
}