More on 'this' variable:
https://docs.oracle.com/javase/tutorial/java/javaOO/thiskey.html

More on class methods and fields:
https://docs.oracle.com/javase/tutorial/java/javaOO/classvars.html

class Point {
    int x,y;

    Point(int a, int b) {
        x = a;
        y = b;
    }
 
    // the hidden 'this' argument is the object
    // on which the method is called
    void move(int dx, int dy) {
        x += dx;     // short form of this.x += dx
        y += dy;     // short form of this.y += dy
    }
}

---------
  void m () {
    Point p = new Point(0,1);
    p.move(1,2);               // this == p             
    ...
  }

--------------

The above could be written as:

class Point {
    int x,y;

    // here the parameter x shadows the object field
    // using 'this' is necessary to refer the object field
    Point(int x, int y) {
        // x = x;   <- WARNING! This would left this.x initialized to 0.
        this.x = x;
        this.y = y;
    }

    void move(int dx, int dy) { 
        this.x += dx;    // same as x += dx
        this.y += dy;    // same as y += dy
    }
}

---------
  void m () {
    Point p = new Point(0,1);
    p.move(1,2);              // here this == p   
    ...
  }

-------

class Point {
    int x,y;

    // class method -> doesn't have extra this variable
    // can access fields x and y through a Point object only
    static Point makePoint(int x, int y) {
        Point p = new Point();
        // this.x = x;  <- ERROR!
        p.x = x;
        p.y = y;
        return p;
    }

    void move(int dx, int dy) { 
        this.x += dx;    // same as x += dx
        this.y += dy;    // same as y += dy
    }
}

---------
  void m () {
    Point p = Point.makePoint(1,2);
    ...
  }