Instanceof in java

[Varadhan Sesharaman]

Hi guys.......

I want to know what is instanceof in java?

I googled it but i can't find a correct and simple def for it.

And also i want to know what is the usage of Instanceof in normal application.



Thanks in advance

[Praveen Kumar M K]

Varadhan Sesharaman wrote:
I googled it but i can't find a correct and simple def for it.

Am surprised

instanceof is an operator used to check whether a particular reference variable(or instance variable) is of the type of a particular class. The instanceof check returns either a true or a false.

Example :

//Say you had a class Dog
Dog dogReference = new Dog();
if(dogReference instanceof Dog) {
  print("Instance of Dog");//Gets printed
}

//Likewise
if(dogReference instanceof Integer) {
  print("Instance of Integer");
} else {
  print("Not an instance of Integer");//Gets printed
}

[Seetharaman Venkatasamy]

Varadhan Sesharaman wrote:
And also i want to know what is the usage of Instanceof in normal application.

for instance, look java.lang.String#equals(Object)

[Jim Pouwels]

Praveen Kumar M K wrote:

Varadhan Sesharaman wrote:
I googled it but i can't find a correct and simple def for it.

Am surprised

instanceof is an operator used to check whether a particular reference variable(or instance variable) is of the type of a particular class. The instanceof check returns either a true or a false.

Example :

//Say you had a class Dog
Dog dogReference = new Dog();
if(dogReference instanceof Dog) {
  print("Instance of Dog");//Gets printed
}

//Likewise
if(dogReference instanceof Integer) {
  print("Instance of Integer");
} else {
  print("Not an instance of Integer");//Gets printed
}

Good explanation. Except for the fact that

dogReference instanceof Integer

won't even compile since they are not in the same inheritance tree.

[Varadhan Sesharaman]

Thank you guys for explaining in a simplw way.


I got the point now.

[Seetharaman Venkatasamy]

Varadhan Sesharaman wrote:
I got the point now.

[Campbell Ritchie]

When you have that sort of question, you should look in the Java Language Specification, where you find it tests whether

the reference could be cast (§15.16) to the ReferenceType without raising a ClassCastException.

It returns false if you put null as its left-hand operand. The right-hand operand can be a class name or an interface name.

Its use in normal programming: as little as possible.

[Praveen Kumar M K]

Jim Pouwels wrote:

dogReference instanceof Integer

won't even compile since they are not in the same inheritance tree.

Oops! Thanks for the correction!