Using the this Keyword
Within an instance method or a constructor,
Using
The most common reason for using the
For example, the
but it could have been written like this:
Each argument to the constructor shadows one of the object's fields — inside the constructor
Using
From within a constructor, you can also use the
This class contains a set of constructors. Each constructor initializes some or all of the rectangle's member variables. The constructors provide a default value for any member variable whose initial value is not provided by an argument. For example, the no-argument constructor calls the four-argument constructor with four 0 values and the two-argument constructor calls the four-argument constructor with two 0 values. As before, the compiler determines which constructor to call, based on the number and the type of arguments.
If present, the invocation of another constructor must be the first line in the 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 thispublic class Point {
public int x = 0;
public int y = 0;
//constructor
public Point(int a, int b) {
x = a;
y = b;
}
}
public class Point {
public int x = 0;
public int y = 0;
//constructor
public Point(int x, int y) {
this.x = x;
this.y = y;
}
}
x is a local copy of the constructor's first argument. To refer to the Point field x, the constructor must use this.x.
Using this with a Constructor
From within a constructor, you can also use the this keyword to call another constructor in the same class. Doing so is called an explicit constructor invocation. Here's another Rectangle class, with a different implementation from the one in the Objects section.public class Rectangle {
private int x, y;
private int width, height;
public Rectangle() {
this(0, 0, 0, 0);
}
public Rectangle(int width, int height) {
this(0, 0, width, height);
}
public Rectangle(int x, int y, int width, int height) {
this.x = x;
this.y = y;
this.width = width;
this.height = height;
}
...
}
If present, the invocation of another constructor must be the first line in the constructor.
