What is the 'instanceof' operator used for in Java?

Question

What is the instanceof operator used for? I\'ve seen stuff like

if (source instanceof Button) {
    //...
} else {
    //...
}

Answer 1

Instance of keyword is helpful when you want to know particular object's instance .

Suppose you are throw exception and when you have catch then perform sum custom operation and then again continue as per your logic (throws or log etc)

Example : 1) User created custom exception "InvalidExtensionsException" and throw it as per logic

2) Now in catch block catch (Exception e) { perform sum logic if exception type is "InvalidExtensionsException"

InvalidExtensionsException InvalidException =(InvalidExtensionsException)e;

3) If you are not checking instance of and exception type is Null pointer exception your code will break.

So your logic should be inside of instance of if (e instanceof InvalidExtensionsException){ InvalidExtensionsException InvalidException =(InvalidExtensionsException)e; }

Above example is wrong coding practice However this example is help you to understand use of instance of it.