如何创建对象的副本 [英] How to create a copy of an object

问题描述

我想要复制一组作为对象的卡片;

以下是我的代码，但我得到此错误线程main中的异常java.lang.StackOverflowError当我运行。我是多么兴奋得到一个包然后还给它。



我尝试过的事情：

< pre>公共类套餐{
 
 / ** 
 *卡片列表
 * / 
私人元素myCards; 
 
 public Pack copy（）{
 if（this.myCards == null）{
 return null; 
} else {
 
 Pack pack =（Pack）this.copy（）; 
返回包; 
 
} 
 
} 

解决方案

嗯，看看你在做什么这里：

包装副本（）{
包装包=（包装）this.copy（）; 
返回包; 

这是调用你所使用的相同方法（递归）。没有任何出路，这将使自己死亡，你将得到一个堆栈溢出。



你想要的是：



包装p =新包装（）;

p.myCards = //在此复制mycards。

返回p;

尝试深度复制您的对象，请参阅： JavaTechniques»更快的深度Java对象的副本 [ ^ ]

您的副本方法除了无限地调用自身外什么都不做。



有一个工具可以让你看到你的代码在做什么，它的名字是调试器。它也是一个很好的学习工具，因为它向你展示了现实，你可以看到哪种期望与现实相符。

当你不明白你的代码在做什么或为什么它做它做的时候，答案就是答案是调试器。

使用调试器查看代码正在执行的操作。只需设置断点并查看代码执行情况，调试器允许您逐行执行第1行并在执行时检查变量。



调试器 - 维基百科，免费的百科全书 [ ^ ]

http://docs.oracle.com/javase/7/docs/technotes/tools/windows/jdb.html [ ^ ]

https://www.jetbrains.com/idea/help/debugging-your-first-java-application.html [ ^ ]

调试器在这里向您展示你的代码正在做，你的任务是与它应该做的事情进行比较。

调试器中没有魔法，它没有找到错误，它只是帮助你。当代码没有达到预期的效果时，你就会接近一个错误。

I want to copy a pack of cards which is an object;
below is my code to do that, but I get this error Exception in thread "main" java.lang.StackOverflowError when i run it. how excatly i am to get a pack and return it.

What I have tried:

<pre>public class Pack {

    /**
     * a list of cards
     */
    private Element myCards;

 public Pack copy() {
        if(this.myCards==null){
            return null;
        }else{
         
         Pack pack= (Pack) this.copy();
         return pack;
           
         }
            
        }

解决方案

Um, look at what you are doing here:

Pack copy() {
         Pack pack= (Pack) this.copy();
         return pack;

This is calling the same method that you are in (recursion). With no way out, this will recurse itself to death, and you will get a stack overflow.

What you want is:

Pack p = new Pack();
p.myCards = // Make a copy of mycards here.
return p;

Try deep copying your object, see this : JavaTechniques » Faster Deep Copies of Java Objects[^]

Your copy method does nothing but calling itself infinitely.

There is a tool that allow you to see what your code is doing, its name is debugger. It is also a great learning tool because it show you reality and you can see which expectation match reality.
When you don't understand what your code is doing or why it does what it does, the answer is debugger.
Use the debugger to see what your code is doing. Just set a breakpoint and see your code performing, the debugger allow you to execute lines 1 by 1 and to inspect variables as it execute.

Debugger - Wikipedia, the free encyclopedia[^]
http://docs.oracle.com/javase/7/docs/technotes/tools/windows/jdb.html[^]
https://www.jetbrains.com/idea/help/debugging-your-first-java-application.html[^]
The debugger is here to show you what your code is doing and your task is to compare with what it should do.
There is no magic in the debugger, it don't find bugs, it just help you to. When the code don't do what is expected, you are close to a bug.

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