谨慎的覆盖clone

最新推荐文章于 2021-05-17 08:46:20 发布

原创最新推荐文章于 2021-05-17 08:46:20 发布 · 658 阅读

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本文介绍了使用Java实现的简单栈类Stack，包括其基本属性、核心方法（如push、pop、isEmpty）以及如何实现复制栈（clone）的功能。通过实例演示了如何使用该类进行元素的压入和弹出操作，并验证了复制操作的有效性。

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Stack.java

源码：

import java.util.Arrays;



public class Stack implements Cloneable {
    private Object[] elements;
    private int size = 0;
    private static final int DEFAULT_INITIAL_CAPACITY = 16;


    public Stack() {
        this.elements = new Object[DEFAULT_INITIAL_CAPACITY];
    }


    public void push(Object e) {
        ensureCapacity();
        elements[size++] = e;
    }


    public Object pop() {
        if (size == 0)
            throw new EmptyStackException();
        Object result = elements[--size];
        elements[size] = null; // Eliminate obsolete reference
        return result;
    }


    public boolean isEmpty() {
        return size == 0;
    }


    @Override public Stack clone() {
        try {
            Stack result = (Stack) super.clone();
            result.elements = elements.clone();
            return result;
        } catch (CloneNotSupportedException e) {
            throw new AssertionError();
        }
    }


    // Ensure space for at least one more element.
    private void ensureCapacity() {
        if (elements.length == size)
            elements = Arrays.copyOf(elements, 2 * size + 1);
    }


    // To see that clone works, call with several command line arguments
    public static void main(String[] args) {
        Stack stack = new Stack();
        for (String arg : args)
            stack.push(arg);
        Stack copy = stack.clone();
        while (!stack.isEmpty())
            System.out.print(stack.pop() + " ");
        System.out.println();
        while (!copy.isEmpty())
            System.out.print(copy.pop() + " ");
    }
}

总结：

clone方法就是另一个构造器，要确保它不会伤害到原始的对象，

并确保正确地创建被克隆对象中的约束条件（invariant）

 @Override public Stack clone() {
        try {
            Stack result = (Stack) super.clone();
            result.elements = elements.clone();
            return result;
        } catch (CloneNotSupportedException e) {
            throw new AssertionError();
        }
    }

有的时候需要单独的拷贝