如何处理Java中的空参数？

我有一个简单的程序，它读取参数并作为结果输出它们

例如，如果我使用：

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

应返回：

1.0 x 2.0, color: RED

但如果我输入以下参数会怎样：

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

以下是我代码的一部分：

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{}表示宽度，但由于它是一个基本类型，因此无法工作……有人能告诉我，如果使用空参数，如何打印默认值吗？谢谢你的帮助

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;
}

也可以在成员声明中指定默认值：

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

并且具有类似的声明，形状成员具有默认值

或者，您可以根据Seelenvirtuose的建议，从无参数构造函数调用不同的构造函数：

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

---

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;
}

也可以在成员声明中指定默认值：

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

并且具有类似的声明，形状成员具有默认值

或者，您可以根据Seelenvirtuose的建议，从无参数构造函数调用不同的构造函数：

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

---

您应该始终在构造函数中为对象属性设置一个值。在您的情况下，您可以定义默认构造函数来调用带有参数的构造函数，并将默认值传递给它：

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

---

您应该始终在构造函数中为对象属性设置一个值。在您的情况下，您可以定义默认构造函数来调用带有参数的构造函数，并将默认值传递给它：

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

---

我不完全理解这个问题，但这可能会有帮助，如果你想知道其他事情，就说吧

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

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

---

我不完全理解这个问题，但这可能会有帮助，如果你想知道其他事情，就说吧

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

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

---

您可以在构造函数中定义默认值

public class Rectangle extends Shape {

    private final double DEFAULT_WIDTH=1.0;
    private final double DEFAULT_LENGTH=1.0;
    private final String DEFAULT_COLOUR="RED";
    private final boolean DEFAULT_FILLED=true;

    protected double width;
    protected double length;

    public Rectangle() {
        this(DEFAULT_WIDTH, DEFAULT_LENGTH, DEFAULT_COLOUR, DEFAULT_FILLED); 
    }

    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";
        }
    }
}

---

您可以在构造函数中定义默认值

public class Rectangle extends Shape {

    private final double DEFAULT_WIDTH=1.0;
    private final double DEFAULT_LENGTH=1.0;
    private final String DEFAULT_COLOUR="RED";
    private final boolean DEFAULT_FILLED=true;

    protected double width;
    protected double length;

    public Rectangle() {
        this(DEFAULT_WIDTH, DEFAULT_LENGTH, DEFAULT_COLOUR, DEFAULT_FILLED); 
    }

    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";
        }
    }
}

---

if width==0{-比较，不是赋值。没有空参数。if width==0{-比较，不是赋值。没有空参数。更好：公共矩形{this1.0，1.0，红色，true；}更好：公共矩形{this1.0，1.0，红色，true；}