instanceof operator vs isInstance() method in Java – GeeksforGeeks
original source : http://www.geeksforgeeks.org/instanceof-operator-vs-isinstance-method-in-java/
instanceof operator vs isInstance() method in Java
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. 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);