Java Tutorial/Operators/instanceof

Finding Out of what Class an Object is Instantiated

   <source lang="java">

import java.util.ArrayList; import java.util.Vector; public class Main {

 public static void main(String[] args) {
   Object testObject = new Vector();
   if (testObject instanceof Vector)
     System.out.println("Object was an instance of the class java.util.Vector");
   else if (testObject instanceof ArrayList)
     System.out.println("Object was an instance of the class java.util.ArrayList");
   else
     System.out.println("Object was an instance of the " + testObject.getClass());
 }

} //Object was an instance of the class java.util.Vector</source>

Identifying Objects

   <source lang="java">

class Animal {

 public String toString() {
   return "This is an animal ";
 }

} class Dog extends Animal {

 public void sound() {
   System.out.println("Woof Woof");
 }

} public class MainClass {

 public static void main(String[] a) {
   Dog aDog = new Dog();
   if (aDog instanceof Animal) {
     Animal ani = (Animal) aDog;
     System.out.println(ani);
   }
 }

}</source>

This is an animal

instanceof operator and class hierarchy

   <source lang="java">

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");
 }

}</source>

The instanceof Keyword

The instanceof keyword can be used to test if an object is of a specified type.

   <source lang="java">

if (objectReference instanceof type)</source>

true