如何处理Java中的空参数？

Question

我有一个简单的程序,它读取参数参数并输出结果.

例如,如果我使用:

Rectangle r1 = new Rectangle(1.0, 2.0, "RED", false);
System.out.println(r1);

应该返回:

1.0 x 2.0, color: RED

但是如果我输入以下参数怎么办:

Rectangle r8 = new Rectangle();
System.out.println(r8);

当使用上述参数时,我的程序如何输出以下默认结果？

1.0 x 1.0, filled with RED

这是我的代码的一部分:

public class Rectangle extends Shape {

    protected double width;
    protected double length;

    public Rectangle() {
        super();
    }

    public Rectangle(double width, double length) {
        super();
        this.width = width;
        this.length = length;
    }

    public Rectangle(double width, double length, String color, boolean filled) {
        super(color, filled);
        this.width = width;
        this.length = length;
    }

    public double getWidth() {
        return width;
    }

    public void setWidth(double width) {
        this.width = width;
    }

    public double getLength() {
        return length;
    }

    public void setLength(double length) {
        this.length = length;
    }   

    public double getArea() {
        return (width * length);
    }

    public double getPerimeter() {
        return (2 * (width + length));
    }

    public String toString() {
        if (super.isFilled()) {
        return width + " x " + length + ", " + "filled with RED";
        } else {
        return width + " x " + length + ", " + "color: RED";
        }
    }
}

我尝试使用if(width = 0){}作为宽度,但因为它是一个原始类型所以它不起作用...任何人都可以告诉我如果使用空参数我怎么能打印出默认值？将不胜感激...谢谢!

Answer 1

您可以在无参数构造函数中设置默认值:

public Rectangle() {
    super("RED", true);
    this.width = 1.0;
    this.length = 1.0;
}

或者您可以在成员声明中指定默认值:

protected double width = 1.0;
protected double length = 1.0;

并有一个类似的声明与Shape成员的默认值.

或者你可以从无参数构造函数中调用另一个构造函数,如Seelenvirtuose所建议的:

public Rectangle() {
    this(1.0, 1.0, "RED", true);
}