Understanding this: A Guide to Java Constructors

Why fields get shadowed, and how this helps you reference them correctly

What is this keyword in Java?

Within an instance method or a constructor, this is a reference to the current object — the object whose method or constructor is being called. You can refer to any member of the current object from within an instance method or a constructor by using this.

Using this with a Field

The most common reason for using the this keyword is because a field is shadowed by a method or constructor parameter.

For example, the Point class was written like this

// Online Java Compiler
// Use this editor to write, compile and run your Java code online

class Point{
    int x, y;
    Point(int x, int y){
        x=x;
        y=y;
    }
    public int getX(){
        return x;
    }
    public int getY(){
        return y;
    }
}
class Main {
    public static void main(String[] args) {
        Point point = new Point(1,2);
        System.out.println("x value is "+point.getX());
        System.out.println("y value is "+point.getY());
    }
}

In the example above, the fields x and y are shadowed by the constructor parameters.