这个Point board = Point[10]是Point的一个新实例吗？

Question

我做了这个练习，他们问我创建了多少个Point实例，他们回答14，但我数了13，因为我不把棋盘算作实例。是吗？为什么呢？因为对我来说，我们创建了一个有10位Point大小的新棋盘，但我们没有实例化它，因为我们需要x和y来做不？

public class Point {
    
    private double x, y;

    public Point(double x, double y) {
        this.x = x;
        this.y = y;
    }

    public Point addition(Point p) {
        return new Point(x + p.x, y + p.y);
    }

    public String toString() {
        return "Point [x=" + x + " , y=" + y + "]";
    }
}

public class Test {
    
    public static void main(String[] args) {
        Point p = new Point(1, 1);
        Point[] board = new Point[10];
        
        for (int i = 0; i < 6; i++)
            tab[i] = p.addition(new Point(i, 1));
            
        System.out.println(p);
        Point p2 = p;
        p2 = p.addition(tab[0]);
        System.out.println(p + " " + p2);
    }
}

Answer 1

是的，你的逻辑是正确的。创建board (Point的数组)不需要创建任何Point实例。它只是一个数组。

但在代码中创建了14个Point实例：

第3行的

1. 创建其中有6个是在addition方法调用中创建的。
2. One在第9行(在addition方法中)。

​

我想你错过了最后一个:)

Answer 2

请看下面的代码，它被创建了14次。我添加了一个静态方法和静态对象来计算对象的个数。另外，你可以把调试点放在构造器中，检查你自己，它是如何被调用的。

public class Point
{

    private double x, y;
    private static int objectCount;//Counter to keep track of objects

    public  static int getObjectCount()
    {
        return objectCount;
    }
    public Point(double x, double y)
    {
        this.x = x;
        this.y = y;
        objectCount++;
    }

    public Point addition(Point p)
    {
        return new Point (x + p.x, y + p.y );
    }

    public String toString()
    {
        return "Point [x=" + x + " , y=" + y + "]";
    }
}

更改测试类以在不同阶段打印此计数

public class Test
{
    public static void main(String[] args)
    {
        Point p = new Point(1, 1);
        System.out.println("No of Objects created after new Point(1, 1) = " + Point.getObjectCount());
        Point[] board = new Point[10];
        for (int i = 0; i < 6; i++)
            board[i] = p.addition(new Point(i, 1));
        System.out.println("No of Objects created after  for loop  = " + Point.getObjectCount());
        System.out.println(p);
        Point p2 = p;
        p2 = p.addition(board[0]);
        System.out.println("No of Objects created after  p.addition(board[0]) = " + Point.getObjectCount());
        System.out.println(p + " " + p2);
    }
}

O/P是

No of Objects created after new Point(1, 1) = 1
No of Objects created after  for loop  = 13
Point [x=1.0 , y=1.0]
No of Objects created after  p.addition(board[0]) = 14
Point [x=1.0 , y=1.0] Point [x=2.0 , y=3.0]