Mega Code Archive
0162 Using instanceof
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Java provides the run-time operator instanceof to check class type for an object. The instanceof operator has this general form:
object instanceof type
The following program demonstrates instanceof:
class A {
}
class B {
}
class C extends A {
}
class D extends A {
}
public class Main{
public static void main(String args[]) {
A a = new A();
B b = new B();
C c = new C();
D d = new D();
if (a instanceof A)
System.out.println("a is instance of A");
if (b instanceof B)
System.out.println("b is instance of B");
if (c instanceof C)
System.out.println("c is instance of C");
if (c instanceof A)
System.out.println("c can be cast to A");
if (a instanceof C)
System.out.println("a can be cast to C");
A ob;
ob = d; // A reference to d
System.out.println("ob now refers to d");
if (ob instanceof D)
System.out.println("ob is instance of D");
ob = c; // A reference to c
System.out.println("ob now refers to c");
if (ob instanceof D)
System.out.println("ob can be cast to D");
else
System.out.println("ob cannot be cast to D");
if (ob instanceof A)
System.out.println("ob can be cast to A");
// all objects can be cast to Object
if (a instanceof Object)
System.out.println("a may be cast to Object");
if (b instanceof Object)
System.out.println("b may be cast to Object");
if (c instanceof Object)
System.out.println("c may be cast to Object");
if (d instanceof Object)
System.out.println("d may be cast to Object");
}
}
The output from this program is shown here:
a is instance of A
b is instance of B
c is instance of C
c can be cast to A
ob now refers to d
ob is instance of D
ob now refers to c
ob cannot be cast to D
ob can be cast to A
a may be cast to Object
b may be cast to Object
c may be cast to Object
d may be cast to Object
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