Java this Keyword

The this keyword in Java refers to the current object. Any member of the current object can be referred to by using the this keyword from within a constructor or an instance method.

The this keyword can only be used within a constructor and an instance method.

Example

public class Student {

    private String fullName;
    private String email;

    /* this keyword within a constructor */
    public Student(String fullName, String email) {
        this.fullName = fullName;
        this.email = email;
    }

    /* this keyword within an instance method */
    public void setStudent(String fullName, String email) {
        this.fullName = fullName;
        this.email = email;
    }
}

The this keyword is usually used to refer to the member of the current object.

Uses of the this keyword

• The this keyword can be used to invoke the constructor of the current Class.
• The this keyword can be used to assign value to the field of the current Class.
• The this keyword can be used to invoke the method of the current Class
• The this keyword can be used to pass argument in the constructor call.
• The this keyword can be used to pass argument in the method call
• The this keyword can be used to return the object of the current Class.

Explicit Constructor Invocation

The this keyword can be used to call another constructor from within a constructor of the same class.

The invoking of a constructor from within different constructor of the same class is called explicit constructor invocation.

Example

Here is an example of a Square class that contains three constructors. Each constructor initializes the values of some or all of the Square's fields:

public class Square {

    private double height;
    private double width;
    private int x;
    private int y;

    public Square() {
        this(2, 2, 0, 0);
    }

    public Square(double height, double width) {
        this(height, width, 0, 0);
    }

    public Square(double height, double width, int x, int y) {
        this.height = height;
        this.width = width;
        this.x = x;
        this.y = y;
    }
}

If an object of the above Square class is created using no-argument constructor, the class member variables are assigned default values, height is assigned 2, width is assigned 2, x is assigned 0, and y is assigned 0. Similarly, if an object is created using the second constructor, height and width can be assigned a custom value, while x and y are given default values of 0.