java - 使用 clone() 复制字段与复制构造函数 Java

Question

我最近开始学习 Java 编程语言类(class)。通过讲座，我发现这两张幻灯片让我感到困惑:

1.

If the class has a copy constructor, clone() can use the copy constructor to create and return a copy of the object.

public Sale(Sale obj) {
        this.itemName = new String(obj.itemName);
        this.itemPrice = obj.itemPrice;
}
public Sale clone() {
        return new Sale(this);
}

2.

Even though the copy constructor and clone() do the same thing (when implemented like shown previously), in certain situations only clone() can work

这是显示的示例(Sale 和 DiscountSale 在其他地方实现):

public class CopyTest {

    public static Sale[] badCopy(Sale[] a) {
        Sale[] b = new Sale[a.length];
        for (int i = 0; i < a.length; i++)
            b[i] = new Sale(a[i]);
        return b;
    }

    public static Sale[] goodCopy(Sale[] a) {
        Sale[] b = new Sale[a.length];
        for (int i = 0; i < a.length; i++)
            b[i] = a[i].clone();
        return b;
    }

    public static void main(String[] args) {
        Sale[] a = new Sale[2];
        a[0] = new Sale("atomic coffee mug", 130.00);
        a[1] = new DiscountSale("invisible paint", 5.00, 10);
        int i;

        Sale[] b = badCopy(a);

        System.out.println("With copy constructors: ");
        for (i = 0; i < a.length; i++) {
            System.out.println("a[" + i + "] = " + a[i]);
            System.out.println("b[" + i + "] = " + b[i]);
        }

        b = goodCopy(a);

        System.out.println("With clone(): ");
        for (i = 0; i < a.length; i++) {
            System.out.println("a[" + i + "] = " + a[i]);
            System.out.println("b[" + i + "] = " + b[i]);
        }
    }

}

当 clone() 在其实现中使用复制构造函数时，复制构造函数和 clone() 有什么区别？为什么只有一个可以正常工作？

Answer 1

只要组合对象没有任何继承层次结构，最好使用复制构造函数。

克隆不调用构造函数。当您具有复杂的对象组合层次结构时，更喜欢克隆。如果不是，请坚持复制构造函数。