在Java中复制对象 [英] Copy an object in Java

问题描述

我有一个对象，我需要在Java中复制。我需要创建一个副本，并对其进行一些测试，而不改变原始对象本身。

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.

我假设我需要使用clone（）方法，但这是保护。在网上做了一些研究，我可以看到，这可以在我的类中的公共方法覆盖。但我找不到如何做到这一点的解释。

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?

此外，这是实现我需要的最佳方式吗？

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

推荐答案

使用复制构造函数的另一个选项（来自 Java实践）：

Another option by using Copy Constructor (from Java Practices):

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());
    }
} 

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