blocks|key|1427928|text|对于测试代码来说，序列化可能是最安全的答案，特别是如果对象已经是可序列化的，请尝试使用Apache+Commons+SerializationUtils来实现。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1427929|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

For test code Serialization is maybe the safest answer, especially if the object is already Serializable try Apache Commons SerializationUtils for an implementation.

blocks|key|1642840|text|另一种选择是使用复制构造函数(从Java+Practices)：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1642841|public+final+class+Galaxy+{

++++public+Galaxy+(double+aMass,+String+aName)+{
++++++++fMass+=+aMass;
++++++++fName+=+aName;
++++}

++++/**
++++*+Copy+constructor.
++++*/
++++public+Galaxy(Galaxy+aGalaxy)+{
++++++++this(aGalaxy.getMass(),+aGalaxy.getName());
++++++++//no+defensive+copies+are+created+here,+since+
++++++++//there+are+no+mutable+object+fields+(String+is+immutable)
++++}

++++/**
++++*+Alternative+style+for+a+copy+constructor,+using+a+static+newInstance
++++*+method.
++++*/
++++public+static+Galaxy+newInstance(Galaxy+aGalaxy)+{
++++++++return+new+Galaxy(aGalaxy.getMass(),+aGalaxy.getName());
++++}

++++public+double+getMass()+{
++++++++return+fMass;
++++}

++++/**
++++*+This+is+the+only+method+which+changes+the+state+of+a+Galaxy
++++*+object.+If+this+method+were+removed,+then+a+copy+constructor
++++*+would+not+be+provided+either,+since+immutable+objects+do+not
++++*+need+a+copy+constructor.
++++*/
++++public+void+setMass(+double+aMass+){
++++++++fMass+=+aMass;
++++}

++++public+String+getName()+{
++++++++return+fName;
++++}

++++//+PRIVATE+/////
++++private+double+fMass;
++++private+final+String+fName;

++++/**
++++*+Test+harness.
++++*/
++++public+static+void+main+(String...+aArguments){
++++++++Galaxy+m101+=+new+Galaxy(15.0,+"M101");

++++++++Galaxy+m101CopyOne+=+new+Galaxy(m101);
++++++++m101CopyOne.setMass(25.0);
++++++++System.out.println("M101+mass:+"+%2B+m101.getMass());
++++++++System.out.println("M101Copy+mass:+"+%2B+m101CopyOne.getMass());

++++++++Galaxy+m101CopyTwo+=+Galaxy.newInstance(m101);
++++++++m101CopyTwo.setMass(35.0);
++++++++System.out.println("M101+mass:+"+%2B+m101.getMass());
++++++++System.out.println("M101CopyTwo+mass:+"+%2B+m101CopyTwo.getMass());
++++}
}+|code-block|syntax|javascript|1642842|entityMap|0|LINK|mutability|MUTABLE|url|http://www.javapractices.com/topic/TopicAction.do?Id=12^0|G|E|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

Another option by using Copy Constructor (from <a href="http://www.javapractices.com/topic/TopicAction.do?Id=12" rel="noreferrer">Java Practices</a>):

<pre><code>public final class Galaxy {

 public Galaxy (double aMass, String aName) {
 fMass = aMass;
 fName = aName;
 }

 /**
 * Copy constructor.
 */
 public Galaxy(Galaxy aGalaxy) {
 this(aGalaxy.getMass(), aGalaxy.getName());
 //no defensive copies are created here, since 
 //there are no mutable object fields (String is immutable)
 }

 /**
 * Alternative style for a copy constructor, using a static newInstance
 * method.
 */
 public static Galaxy newInstance(Galaxy aGalaxy) {
 return new Galaxy(aGalaxy.getMass(), aGalaxy.getName());
 }

 public double getMass() {
 return fMass;
 }

 /**
 * This is the only method which changes the state of a Galaxy
 * object. If this method were removed, then a copy constructor
 * would not be provided either, since immutable objects do not
 * need a copy constructor.
 */
 public void setMass( double aMass ){
 fMass = aMass;
 }

 public String getName() {
 return fName;
 }

 // PRIVATE /////
 private double fMass;
 private final String fName;

 /**
 * Test harness.
 */
 public static void main (String... aArguments){
 Galaxy m101 = new Galaxy(15.0, "M101");

 Galaxy m101CopyOne = new Galaxy(m101);
 m101CopyOne.setMass(25.0);
 System.out.println("M101 mass: " + m101.getMass());
 System.out.println("M101Copy mass: " + m101CopyOne.getMass());

 Galaxy m101CopyTwo = Galaxy.newInstance(m101);
 m101CopyTwo.setMass(35.0);
 System.out.println("M101 mass: " + m101.getMass());
 System.out.println("M101CopyTwo mass: " + m101CopyTwo.getMass());
 }
} 
</code></pre>

blocks|key|1642923|text|约书亚·布洛赫将带来some+interesting+things+to+say+about+cloneable报道。根据对象的大小/结构，我会向对象添加一个复制构造函数，或者使用上面提到的解决方案之一进行序列化/反序列化。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1642924|entityMap|0|LINK|mutability|MUTABLE|url|http://www.artima.com/intv/bloch13.html^0|A|1A|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

Joshua Bloch has <a href="http://www.artima.com/intv/bloch13.html" rel="nofollow noreferrer">some interesting things to say about cloneable</a>. Depending on the size/construction of the object, I'd add a copy constructor to the object, or serialise/deserialise using one of the solutions mentioned above.

blocks|key|1428135|text|有两种流行的方法。一种是提供您提到的clone方法，如下所示。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1428136|public+class+C+implements+Cloneable+{
++++@Override+public+C+clone()+{
++++++++try+{
++++++++++++final+C+result+=+(C)+super.clone();
++++++++++++//+copy+fields+that+need+to+be+copied+here!
++++++++++++return+result;
++++++++}+catch+(final+CloneNotSupportedException+ex)+{
++++++++++++throw+new+AssertionError();
++++++++}
}|code-block|syntax|javascript|1428137|注意“复制字段...在这里！”部分。初始result只是一个浅拷贝，这意味着如果有对对象的引用，则原始对象和result将共享同一对象。例如，如果C包含private+int[]+data，您可能希望复制它。|1428138|...
final+C+result+=+(C)+super.clone();
result.data+=+data.clone();
return+result;
...|1428139|请注意，您不需要复制原始字段，因为它们的内容已经被复制，或者不可变的对象，因为它们无论如何都不能改变。|1428140|第二种方法是提供一个复制构造函数。|1428141|public+class+C+{
++++public+C(final+C+c)+{
++++++++//+initialize+this+with+c
++++}
}|1428142|或者是一个复制品工厂。|1428143|public+class+C+{
++++public+static+C+newInstance(final+C+c)+{
++++++++return+new+C(c);
++++}

++++private+C(final+C+c)+{
++++++++//+initialize+this+with+c
++++}
}|1428144|这两种方法都有各自的属性。clone很好，因为它是一个方法，所以你不需要知道确切的类型。最后，你应该总是得到一个“完美”的副本。复制构造函数很好，因为调用者有机会做出决定，这可以从Java集合中看到。|1428145|final+List+c+=+...+
//+Got+c+from+somewhere+else,+could+be+anything.
//+Maybe+too+slow+for+what+we're+trying+to+do?

final+List+myC+=+new+ArrayList(c);
//+myC+is+an+ArrayList,+with+known+properties|1428146|我建议选择任何一种更适合您的方法。|1428147|我只在单元测试中使用其他方法，如反射复制或立即序列化/反序列化。对我来说，它们感觉不太适合生产代码，主要是因为性能方面的考虑。|1428148|entityMap^0|I|5|0|0|K|6|1I|6|21|1|24|I|0|0|0|0|0|0|0|D|5|0|0|0|0^^$0|@$1|2|3|4|5|6|7|18|8|@$9|19|A|1A|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|1B|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|1C|8|@$9|1D|A|1E|B|C]|$9|1F|A|1G|B|C]|$9|1H|A|1I|B|C]|$9|1J|A|1K|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|1L|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|1M|8|@]|D|@]|E|$]]|$1|Q|3|R|5|6|7|1N|8|@]|D|@]|E|$]]|$1|S|3|T|5|H|7|1O|8|@]|D|@]|E|$I|J]]|$1|U|3|V|5|6|7|1P|8|@]|D|@]|E|$]]|$1|W|3|X|5|H|7|1Q|8|@]|D|@]|E|$I|J]]|$1|Y|3|Z|5|6|7|1R|8|@$9|1S|A|1T|B|C]]|D|@]|E|$]]|$1|10|3|11|5|H|7|1U|8|@]|D|@]|E|$I|J]]|$1|12|3|13|5|6|7|1V|8|@]|D|@]|E|$]]|$1|14|3|15|5|6|7|1W|8|@]|D|@]|E|$]]|$1|16|3|-4|5|6|7|1X|8|@]|D|@]|E|$]]]|17|$]]

There are two popular approaches. One is to provide a <code>clone</code> method as you mentioned, like so.

<pre><code>public class C implements Cloneable {
 @Override public C clone() {
 try {
 final C result = (C) super.clone();
 // copy fields that need to be copied here!
 return result;
 } catch (final CloneNotSupportedException ex) {
 throw new AssertionError();
 }
}
</code></pre>

Pay attention to the "copy fields ... here!" part. The initial <code>result</code> is only a shallow copy, meaning that if there's a reference to an object, both the original and <code>result</code> will share the same object. For example, if <code>C</code> contains <code>private int[] data</code> you'd probably want to copy that.

<pre><code>...
final C result = (C) super.clone();
result.data = data.clone();
return result;
...
</code></pre>

Note that you don't need to copy primitive fields, as their content is already copied, or immutable objects, as they can't change anyways.

The second approach is to provide a copy constructor.

<pre><code>public class C {
 public C(final C c) {
 // initialize this with c
 }
}
</code></pre>

Or a copy factory.

<pre><code>public class C {
 public static C newInstance(final C c) {
 return new C(c);
 }

 private C(final C c) {
 // initialize this with c
 }
}
</code></pre>

Both approaches have their respective properties. <code>clone</code> is nice because its a method, so you don't have to know the exact type. In the end, you should always end up with a "perfect" copy. The copy constructor is nice because the caller has a chance to decide, as can be seen by the Java Collections.

<pre><code>final List c = ... 
// Got c from somewhere else, could be anything.
// Maybe too slow for what we're trying to do?

final List myC = new ArrayList(c);
// myC is an ArrayList, with known properties
</code></pre>

I recommend choosing either approach, whichever suits you better.

I'd use the other approaches, like reflective copying or immediate serializing/deserializing, in unit tests only. To me, they feel less appropriate for production code, mainly because of performance concerns.

blocks|key|1428181|text|在java中有多种复制对象的方法(浅的或深的)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1428182|此Answer将对您有所帮助。|offset|length|1428183|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/869033/how-do-i-copy-an-object-in-java/9834683#9834683^0|0|1|6|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@$D|P|E|Q|1|R]]|A|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|M]]]]

There are multiple ways to copy object in java(shallow or deep). 
This <a href="https://stackoverflow.com/questions/869033/how-do-i-copy-an-object-in-java/9834683#9834683">Answer</a> will help you.

I have an object that I need to copy in Java. I need to create a copy and run some tests on it without changing the original object itself.

I assumed that I needed to use the clone() method, but this is protected. Having done some research on the net, I can see that this can be overriden with a public method in my class. But I cannot find an explanation on how to do this. How could this be done?

Also, is this the best way of achieving what I need?

Copy an object in Java

单元测试

Java

我有一个需要用Java复制的对象。我需要创建一个副本并在其上运行一些测试，而不更改原始对象本身。我假设我需要使用clone()方法，但这是受保护的。在网上做了一些研究后，我可以看到这可以用我的类中的一个公共方法来覆盖。但我找不到如何做到这一点的解释。如何做到这一点呢？另外，这是实现我所需的最好方法吗？

问在Java中复制对象
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