hashCode 作用，對象根據hashCode的值分區域存放

/**
 * hashCode 作用
 * 
 * @author Administrator
 * 
 */
public class Point {

    public static void main(String[] args) {
        Point p1 = new Point(3, 3);
        Point p2 = new Point(2, 3);
        Point p3 = new Point(3, 3);

        HashSet<Point> set
 
 = new HashSet<>();

        set.add(p1);
        set.add(p2);
        set.add(p3);
        set.add(p1);
        p1.x = 7;
        // 修改equals 中的變量的值，hashCode改變，查找的hash區域變化，在新計算的區域p1無法找到，無法刪除，最後可能引起內存泄漏
        set.remove(p1);
        System.out.println(set.size());
    }

    int x;

    
 
int y;

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

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + x;
        result = prime * result + y;
        return
 
 result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Point other = (Point) obj;
        if (x != other.x)
            return false;
        if (y != other.y)
            return false;
        return true;
    }

}

java hashCode 作用