Java 多重构造函数设置问题

Question

所以我在使用多个构造函数时遇到问题。基本上，我有两个 WaterDrop 构造，我将初始 x 和 y 位置(第二个代码块)传递到适当的构造函数中。问题是它没有将 int x, y 实例变量设置到适当的起始位置。它在第一个构造函数中将它们设置得很好，但是当它使用第二个构造函数绘制点时，它会自动将它们设置为 (0, 0) 位置。无论如何，我可以调用第一个构造函数，以便将 x 和 y 位置设置为适当的起始位置吗？

public class WaterDrop
{
// instance variables - replace the example below with your own
private int x;
private int y;
private int xVelocity;
private int yVelocity;
private DrawingPanel panel;
private static int DIAMETER = 1;
private int delayStart;
private int bounceLimit;

private static Random rand = new Random();

public WaterDrop(int x, int y){
    this.x = x; //**These assign just fine but I can't get them to get passed**
    this.y = y;  //**into the next WaterDrop constructor**
                 //**i.e. (200, 400)**

}

public WaterDrop(DrawingPanel panel, boolean move)
{
    //initialise instance variables //**In this constructor they are still**
                                    //**initialized to 0**
    this.panel = panel;  //**Since they are initialized at 0, when I draw the**
                         //**waterDrops they appear at the location (0, 0)**

}

    xVelocity = rand.nextInt(3) - 1;
    yVelocity = rand.nextInt(20) + 1 ;
    delayStart = rand.nextInt(100);
    bounceLimit = 0;

}

这是我从 WaterFountain 类传递的内容:

public class WaterFountain{
....

public WaterFountain(DrawingPanel panel, int xLocation, int yLocation)
{
    this.panel = panel;
    this.xLocation = xLocation;
    this.yLocation = yLocation;

    for(int i = 0; i < NUM_WATER_DROPS; i++){
         waterDrop[i] = new WaterDrop(this.xLocation, this.yLocation);
    }
}


....
}

Answer 1

您的第二个构造函数不能神奇地“知道”x 和 y 的适当值。您必须给它适当的值。唯一的方法是向其添加 int x 和 int y 参数。然后，您可以通过调用第一个构造函数来设置 x 和 y 实例变量:

public WaterDrop(int x, int y, DrawingPanel panel, boolean move)
{
    this(x, y);  // invoke the WaterDrop(int, int) ctor
    this.panel = panel;  
}

或者直接设置x和y:

public WaterDrop(int x, int y, DrawingPanel panel, boolean move)
{
    this.x;
    this.y;
    this.panel = panel;  
}