instanceof operator and isInstance() method both are used for checking the class of the object. But main difference comes when we want to check the class of object dynamically. In this case isInstance() method will work. There is no way we can do this by instanceof operator.
instanceof operator and isInstance() method both return a boolean value. isInstance() method is a method of class Class in java while instanceof is a operator.
Consider an example:
// Java program to demonstrate working of // instanceof operator public class Test { public static void main(String[] args) { Integer i = new Integer( 5 ); // prints true as i is instance of class // Integer System.out.println(i instanceof Integer); } } |
Output:
true
Now if we want to check the class of the object at run time, then we must use isInstance() method.
// Java program to demonstrate working of isInstance() // method public class Test { // This method tells us whether the object is an // instance of class whose name is passed as a // string 'c'. public static boolean fun(Object obj, String c) throws ClassNotFoundException { return Class.forName(c).isInstance(obj); } // Driver code that calls fun() public static void main(String[] args) throws ClassNotFoundException { Integer i = new Integer( 5 ); // print true as i is instance of class // Integer boolean b = fun(i, "java.lang.Integer" ); // print false as i is not instance of class // String boolean b1 = fun(i, "java.lang.String" ); /* print true as i is also instance of class Number as Integer class extends Number class*/ boolean b2 = fun(i, "java.lang.Number" ); System.out.println(b); System.out.println(b1); System.out.println(b2); } } |
Output:
true false true
NOTE: instanceof operator throws compile time error(Incompatible conditional operand types) if we check object with other classes which it doesn’t instantiate.
public class Test { public static void main(String[] args) { Integer i = new Integer( 5 ); // Below line causes compile time error:- // Incompatible conditional operand types // Integer and String System.out.println(i instanceof String); } } |
Output :
13: error: incompatible types: Integer cannot be converted to String System.out.println(i instanceof String); ^
Related Articles:
new operator vs newInstance() method in Java
Reflections in Java
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