[Java] Instanceof

 Instanceof

- instanceof operator is used to test whether the object is an instance of the specified type

- It is also known as type comparison operator

- It returns either true or false

1. Example

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public class Test{     public static void main(String[]args){         Test a = new Test();         System.out.println(a instanceof Test);     } }

- true

2. instanceof in java with a variable that have null value

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public class Test{     public static void main(String[]args){         Test a = null;         System.out.println(a instanceof Test);     } }

 

- false

3. Downcasting with java instanceof operator

1) Downcasting

- When subclass type refers to the object of Parent class, it is known as downcasting

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1	Dog d = new AnImal(); //Compilation error

 

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1	Dog d = (Dog) new Animal() // ClassCastException

 

2) Possibility of downcasting with instanceof

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package statics;   class Animal{       }   class Dog extends Animal{           static void method(Animal a){         if(a instanceof Dog){             Dog d = (Dog)a;//down         }     }       }   public class Test{     public static void main(String[]args){         Animal a = new Dog();         Dog.method(a);     } }

 

3) Downcasting without the use of instanceof

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class Animal{       }   class Dog extends Animal{           static void method(Animal a){             Dog d = (Dog)a;//down     }       }   public class Test{     public static void main(String[]args){         Animal a = new Dog();         Dog.method(a);     } }