java两个构造函数？

Question

我已经用setter和getter完成了我的任务（我是用OOD完成的），但是我仍然不明白这两个Rectangle方法的目的是什么，如果我删除了空的Rectangle，就会出现一个错误：

注意，这不是完整的代码

// private double length = 25.0;
private double width = 15.5;

public Rectangle(){

}

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

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

public double getLength(){
    return length;
}

public double getWidth(){
    return width;
}

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

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

public static void print(){
    Rectangle rt = new Rectangle();
    Box box = new Box();
    System.out.println("The rectangle has a length of " + rt.getLength() + " and a width of " + rt.getWidth() );
    System.out.println("The rectangle has an area of "+ rt.area());
    System.out.println("The rectangle has a perimeter of "+ rt.perimeter());
    box.print();
}

Answer 1

这是默认（无参数）构造函数。由于您有另一个构造函数，如果不显式定义，Java将不会隐式创建它。因为print方法中的第一行调用了它，所以如果删除它，就会出现错误