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
public class Point {
public int x = 0;
public int y = 0;
//constructor
public Point(int a, int
b) {
x = a;
y = b;
}
}
but it could have been
written like this:
public class Point {
public int x = 0;
public int y = 0;
//constructor
public Point(int x, int
y) {
this.x = x;
this.y = y;
}
}
Each argument to the
constructor shadows one of the object's fields — inside the constructor 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;
}
...
}
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.
Summery:
“this” constructor always calls the current method. It is
used in constructor for the purpose of the calling of the current method. It is
also used for the shortest calling of the method path. But it is the too
shortest path of calling a method.
