Java Tutorial/Operators/instanceof

Finding Out of what Class an Object is Instantiated

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

Identifying Objects

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);
    }
  }
}

This is an animal

instanceof operator and class hierarchy

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");
  }
}

The instanceof Keyword

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

if (objectReference instanceof type)

true