Using the this Keyword - Java Tutorial 5.0 英文版

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Using the this Keyword

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. The most common reason for doing so is that a member variable is hidden by an argument to the method or the constructor.

For example, the following constructor for the HSBColor class initializes the object's member variables according to the arguments passed into the constructor. Each argument to the constructor hides one of the object's member variables, so this constructor must refer to the object's member variables through this:

public class HSBColor {
    private int hue, saturation, brightness;
    public HSBColor (int hue, int saturation,
                     int brightness) {
        this.hue = hue;
        this.saturation = saturation;
        this.brightness = brightness;
    }
}

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 The Life Cycle of an Object 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, using 0s as default values. As before, the compiler determines which constructor to call, based on the number and the type of arguments.

If present, an explicit constructor invocation must be the first line in the constructor.

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