JAVA

this in java

this() : used for calling the constructor . 
  we can only use it in the constructor
this. : used for calling the instance variables 
we can use in any object instances

this keyword in java

/**
 * This keyword,
 * this keyword is a reference variable that refers to the current class
 * instance.
 */
class Student {
    int id;
    String name;

    Student(int id, String name) {
        this.id = id;
        this.name = name;
    }

    void display() {
        System.out.println(this.id);// both way can call
        System.out.println(this.name);
        System.out.println(id);
        System.out.println(name);
    }
}

public class This {
    public static void main(String[] args) {
        Student student = new Student(10, "Mike");
        student.display();
    }
}

this Keyword Java

class Main {
    int instVar;

    Main(int instVar){
        this.instVar = instVar;
        System.out.println("this reference = " + this);
    }

    public static void main(String[] args) {
        Main obj = new Main(8);
        System.out.println("object reference = " + obj);
    }
}

this in java

public class MyThisTest {
  private int a;

  public MyThisTest() {
    this(42); // calls the other constructor
  }

  public MyThisTest(int a) {
    this.a = a; // assigns the value of the parameter a to the field of the same name
  }

  public void frobnicate() {
    int a = 1;

    System.out.println(a); // refers to the local variable a
    System.out.println(this.a); // refers to the field a
    System.out.println(this); // refers to this entire object
  }

  public String toString() {
    return "MyThisTest a=" + a; // refers to the field a
  }
}