Use of instanceof in Java

Question

What is the   39 instanceof  39  operator used for        I learned that Java has the instanceof operator  Can you elaborate where it is used and what are its advantages

User · Answer

instanceof is a keyword that can be used to test if an object is of a specified type   Example    public class MainClass       public static void main String   a         String s    Hello       int i   0      String g      if  s instanceof java lang String              This is going to be printed        System out println  s is a String              if  i instanceof Integer              This is going to be printed as autoboxing will happen  int - gt  Integer         System out println  i is an Integer              if  g instanceof java lang String              This case is not going to happen because g is not initialized and           therefore is null and instanceof returns false for null          System out println  g is a String                Here is my source

User · Answer

instanceof is used to check if an object is an instance of a class  an instance of a subclass  or an instance of a class that implements a particular interface   Read more from the Oracle language definition here

User · Answer

instanceof can be used to determine the actual type of an object   class A       class C extends A      class D extends A       public static void testInstance        A c   new C        A d   new D        Assert assertTrue c instanceof A  amp  amp  d instanceof A       Assert assertTrue c instanceof C  amp  amp  d instanceof D       Assert assertFalse c instanceof D       Assert assertFalse d instanceof C

User · Answer

Basically  you check if an object is an instance of a specific class  You normally use it  when you have a reference or parameter to an object that is of a super class or interface type and need to know whether the actual object has some other type  normally more concrete    Example   public void doSomething Number param      if  param instanceof Double        System out println  param is a Double          else if  param instanceof Integer        System out println  param is an Integer           if  param instanceof Comparable          subclasses of Number like Double etc  implement Comparable       other subclasses might not - gt  you could pass Number instances that don t implement that interface     System out println  param is comparable             Note that if you have to use that operator very often it is generally a hint that your design has some flaws  So in a well designed application you should have to use that operator as little as possible  of course there are exceptions to that general rule

[java] Use of "instanceof" in Java

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