如何在 Java 中复制堆栈? [英] How do I copy a stack in Java?

问题描述

我有一个堆栈 A，我想创建一个与堆栈 A 相同的堆栈 B.我不希望堆栈 B 只是指向 A 的指针——我实际上想创建一个新的堆栈 B，其中包含与堆栈 A 相同的元素，顺序与堆栈 A 相同.堆栈 A 是一个字符串堆栈.

I have a stack A and I want to create a stack B that is identical to stack A. I don't want stack B to simply be a pointer to A -- I actually want to create a new stack B that contains the same elements as stack A in the same order as stack A. Stack A is a stack of strings.

谢谢！

推荐答案

只需使用 Stack-class 的 clone() 方法(它实现了 Cloneable).

Just use the clone() -method of the Stack-class (it implements Cloneable).

这是一个使用 JUnit 的简单测试用例:

Here's a simple test-case with JUnit:

@Test   
public void test()
{
    Stack<Integer> intStack = new Stack<Integer>();
    for(int i = 0; i < 100; i++)        
    {
        intStack.push(i);
    }

    Stack<Integer> copiedStack = (Stack<Integer>)intStack.clone();

    for(int i = 0; i < 100; i++)            
    {
        Assert.assertEquals(intStack.pop(), copiedStack.pop());
    }
}

tmsimont:这会为我创建一个未经检查或不安全的操作"警告.任何如何在不产生此问题的情况下执行此操作?

tmsimont: This creates a "unchecked or unsafe operations" warning for me. Any way to do this without generating this problem?

我起初回答说警告是不可避免的，但实际上使用 <?> (wildcard) -typing 是可以避免的:

I at first responded that the warning would be unavoidable, but actually it is avoidable using <?> (wildcard) -typing:

@Test
public void test()
{
    Stack<Integer> intStack = new Stack<Integer>();
    for(int i = 0; i < 100; i++)
    {
        intStack.push(i);
    }

    //No warning
    Stack<?> copiedStack = (Stack<?>)intStack.clone();

    for(int i = 0; i < 100; i++)
    {
        Integer value = (Integer)copiedStack.pop(); //Won't cause a warning, no matter to which type you cast (String, Float...), but will throw ClassCastException at runtime if the type is wrong
        Assert.assertEquals(intStack.pop(), value);
    }
}

基本上我会说您仍在进行从 ?(未知类型)到 Integer 的未经检查的强制转换，但没有警告.就个人而言，我仍然更喜欢直接转换为 Stack<Integer> 并使用 @SuppressWarnings("unchecked") 抑制警告.

Basically I'd say you're still doing an unchecked cast from ? (unknown type) to Integer, but there's no warning. Personally, I'd still prefer to cast directly into Stack<Integer> and suppress the warning with @SuppressWarnings("unchecked").

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