Java Clone

Java Clone

平时项目中用的也不多，今天来实践下Java的Clone。Clone主要分为“浅拷贝”与“深拷贝”。
“浅拷贝”: 实现Cloneable接口，简单的调用super.clone();即能实现，如:

    @Override
    public Object clone() throws CloneNotSupportedException {
        return super.clone();
    }

“深拷贝”: 虽然实现Cloneable接口也能去实现“深拷贝”，但会非常繁琐，而且引用层级很多的情况下，需要给每个类的clone方法都去添加相应的clone逻辑，所以一般不用。最简单的就是用序列化方式去完成“深拷贝”,如:

public class CloneUtils {
    @SuppressWarnings("unchecked")
    public static <T extends Serializable> T clone(T obj) {
        T cloneObj = null;
        try {
            // 写入字节流
            ByteArrayOutputStream out = new ByteArrayOutputStream();
            ObjectOutputStream obs = new ObjectOutputStream(out);
            obs.writeObject(obj);
            obs.close();

            // 分配内存，写入原始对象，生成新对象
            ByteArrayInputStream ios = new ByteArrayInputStream(out.toByteArray());
            ObjectInputStream ois = new ObjectInputStream(ios);
            // 返回生成的新对象
            cloneObj = (T) ois.readObject();
            ois.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return cloneObj;
    }
}

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举个栗子

Car,有车标CarMark，轮子的集合Tireset
实现Cloneable是为了“浅拷贝”， 实现Serializable是为了“深拷贝”

public class Car implements Cloneable, Serializable{

    private static final long serialVersionUID = 855536990529969854L;
    
    private CarMark carMark;
    
    private LinkedHashSet<Tire> tireSet;

    public Car(CarMark carMark, LinkedHashSet<Tire> tireSet) {
        super();
        this.carMark = carMark;
        this.tireSet = tireSet;
    }

    public CarMark getCarMark() {
        return carMark;
    }

    public void setCarMark(CarMark carMark) {
        this.carMark = carMark;
    }

    public LinkedHashSet<Tire> getTireSet() {
        return tireSet;
    }

    public void setTireSet(LinkedHashSet<Tire> tireSet) {
        this.tireSet = tireSet;
    }

    @Override
    public Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
}

public class CarMark implements Serializable {

    private static final long serialVersionUID = -840209218449463080L;
    
    private String name;
    private int historyInYears;

    public CarMark(String name, int historyInYears) {
        super();
        this.name = name;
        this.historyInYears = historyInYears;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getHistoryInYears() {
        return historyInYears;
    }

    public void setHistoryInYears(int historyInYears) {
        this.historyInYears = historyInYears;
    }

}

public class Tire implements Serializable{

    private static final long serialVersionUID = -4185789610721446662L;
    
    private TirePosition tirePosition;
    private int wear;
    
    public Tire(TirePosition tirePosition, int wear) {
        super();
        this.tirePosition = tirePosition;
        this.wear = wear;
    }
    
    public TirePosition getTirePosition() {
        return tirePosition;
    }
    public void setTirePosition(TirePosition tirePosition) {
        this.tirePosition = tirePosition;
    }
    public int getWear() {
        return wear;
    }
    public void setWear(int wear) {
        this.wear = wear;
    }
    
}

public enum TirePosition{
    LEFT_FRONT, RIGHT_FRONT, LEFT_REAR, RIGHT_REAR 
}

Builder 造车

public class CarBuilder {
    
    public static Car buidFerrari(){
        
        CarMark carMark = new CarMark("Ferrari", 70);
        
        LinkedHashSet<Tire> tireSet = new LinkedHashSet<Tire>();
        tireSet.add(new Tire(TirePosition.LEFT_FRONT, 0));
        tireSet.add(new Tire(TirePosition.RIGHT_FRONT, 0));
        tireSet.add(new Tire(TirePosition.LEFT_REAR, 0));
        tireSet.add(new Tire(TirePosition.RIGHT_REAR, 0));
        
        Car car = new Car(carMark, tireSet);
        
        return car;
        
    }
    
}

Main方法比较“浅拷贝”与“深拷贝”

public class Main {
    public static void main(String[] args) throws CloneNotSupportedException {
        
        Car car = CarBuilder.buidFerrari();
        
        Car clonedCar = (Car) car.clone();
        
        String result = "使用Cloneable接口: " + (car.getCarMark() == clonedCar.getCarMark() ? "clone是浅拷贝的" : "clone是深拷贝的");
        System.out.println(result);
        System.out.println(car.getCarMark().toString());
        System.out.println(clonedCar.getCarMark().toString());
        System.out.println(car.getTireSet().toString());
        System.out.println(clonedCar.getTireSet().toString());
        
        System.out.println("-------------------------------------------");
        
        Car deepClonedCar = CloneUtils.clone(car);
        
        result = "使用序列化方式: " + (car.getCarMark() == deepClonedCar.getCarMark() ? "clone是浅拷贝的" : "clone是深拷贝的");
        System.out.println(result);
        System.out.println(car.getCarMark().toString());
        System.out.println(deepClonedCar.getCarMark().toString());
        System.out.println(car.getTireSet().toString());
        System.out.println(deepClonedCar.getTireSet().toString());
        
    }
}

输出

使用Cloneable接口: clone是浅拷贝的
sample.hibernate4.car.CarMark@70dea4e
sample.hibernate4.car.CarMark@70dea4e
[sample.hibernate4.car.Tire@15db9742, sample.hibernate4.car.Tire@6d06d69c, sample.hibernate4.car.Tire@7852e922, sample.hibernate4.car.Tire@4e25154f]
[sample.hibernate4.car.Tire@15db9742, sample.hibernate4.car.Tire@6d06d69c, sample.hibernate4.car.Tire@7852e922, sample.hibernate4.car.Tire@4e25154f]
-------------------------------------------
使用序列化方式: clone是深拷贝的
sample.hibernate4.car.CarMark@70dea4e
sample.hibernate4.car.CarMark@2f4d3709
[sample.hibernate4.car.Tire@15db9742, sample.hibernate4.car.Tire@6d06d69c, sample.hibernate4.car.Tire@7852e922, sample.hibernate4.car.Tire@4e25154f]
[sample.hibernate4.car.Tire@6f496d9f, sample.hibernate4.car.Tire@723279cf, sample.hibernate4.car.Tire@10f87f48, sample.hibernate4.car.Tire@b4c966a]

从结果看出，通过调用car.clone();方式，不管是Car的引用(CarMark)，还是Car引用的引用（具体某个Tire），都指向同一个对象，这就是“浅拷贝”
而通过调用CloneUtils.clone(car);都是指向不同的对象，这就是“深拷贝”

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Code:

Sample Code on Github

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参考：
Java 7之基础 - 浅克隆与深克隆
Java对象的Clone