This Keyword and Instanceof operator

• The functionality of "this" keyword is only to explicitly point the object because of which the function is currently under execution.
• The object because of which the function is currently under execution is known as current object.
• Thus the functionality of this is to point current class object.

This used to call constructor from another constructor:

Class Tdemo{

Tdemo(){

this(6);

System.out.println("Default constructor")
}

Tdemo(int a ){

this(1,2);

System.out.println("One argument constructor")
}

Tdemo(int a, int b ){

System.out.println("Two argument constructor")
}

public static void main(String args[]){

Tdemo obj= new Tdemo();

}

}

Output:

Two argument constructor

One argument constructor

Default constructor

Program for without this keyword:

class Student{
int id;
String name;
String college;
Student(int id,String name,String college){
id=id;
name=name;
college=college;
}
void display(){
System.out.println(id+" "+name+" "+college);
}
public satic void main(String args[]){
Student s=new Student(1,"Indhu","TRML");
Student s1=new Student(2,"Sindhu","TRML");
s.display();
s1.sispaly();

}

Output:
0 null null
0 null null

in the above program parameters and instance variables are same.so we by using this keyword we can solve this problem.

solution of the above problem using This keyword:

class Student{
int id;
String name;
String college;
Student(int id,String name,String college){
this.id=id;
this.name=name;
this.college=college;
}
void display(){
System.out.println(id+" "+name+" "+college);
}
public satic void main(String args[]){
Student s=new Student(1,"Indhu","TRML");
Student s1=new Student(2,"Sindhu","TRML");
s.display();
s1.sispaly();

}

Output:
1 Indhu TRML
2 Sindhu TRML

Important points of this keyword:

• This is final variable in java.so we can't assign values to the final.
• this=new Emp(); //Can't assign values to this.it will return compilation error.

Limitation of this keyword:

• "this" is applicable to only to the non static methods because static methods are not executed by any object

Instance of operator:

• Instance of operator is used to test whether that object is belong to that class type or not.
• If that object belongs to that class it returns true .otherwise it returns false.
• Instance of operator is also known as comparison operator.because it compares with the instance of type.

Program to instance of operator:

public class Employee{

public static void main(String args[]){

Employee e =new Employee();

System.out.println(e instanceof Employee);//true

}

}

Output:true

public class A{

public void show(){

System.out.println("This is class A");

}

public class B extends A{

public void show(){

System.out.println("This is class B");

}

public static void main(String args[]){

A a=new A();

System.out.println(a instanceof A);

System.out.println(a instanceof B);

}

}

Output:

true

false