clone方法

clone是定義一個(gè)Object類下基本方法之一：

    protected native Object clone() throws CloneNotSupportedException;

使用的時(shí)候需要繼承object對(duì)象，并且為了可以使其它類調(diào)用該方法，覆寫克隆方法時(shí)必須將其作用域設(shè)置為public.

淺拷貝

淺拷貝就拷貝了對(duì)象本身，屬性值不變，也就是說(shuō)對(duì)象里面的引用還是原來(lái)對(duì)象里面的引用

class A implements Cloneable {
    int a = 0;
    int[] b = {1, 2};

    @Override
    protected Object clone() throws CloneNotSupportedException {
        A a = null;
        try {
            a = (A) super.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return a;
    }
}

測(cè)試一下

A a = new A();
A b = (A) a.clone();
System.out.println(b.a);
for (int i :b.b) {
    System.out.print(i);
}
b.a = 1;
b.b[0] = 3;
b.b[1] = 4;
System.out.println(a.a);
for (int i :a.b) {
    System.out.print(i);
}

測(cè)試結(jié)果是:    
        0  1,2
        0  3,4

因?yàn)閍是基本類型所以值不變，但是b是引用類型，所以值也被改變了

深拷貝

和淺拷貝就一些細(xì)微區(qū)別，深拷貝是把對(duì)象中的屬性也進(jìn)行了一個(gè)拷貝

class A implements Cloneable {
    int a = 0;
    int[] b = {1, 2};

    @Override
    protected Object clone() throws CloneNotSupportedException {
        A a = null;
        try {
            a = (A) super.clone();
            // 對(duì)屬性進(jìn)克隆
            a.b = b.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return a;
    }
}

測(cè)試結(jié)果是:    
        0  1,2
        0  1,2

循環(huán)引用

如果類中的對(duì)象引用了其他的對(duì)象，那么一次次去clone顯然不現(xiàn)實(shí)

借助java的序列化,A需要實(shí)現(xiàn)序列化接口，而且A中使用的所有對(duì)象都要實(shí)現(xiàn)序列化接口，否則會(huì)拋出NotSerializableException異常

    @Override
    protected Object clone() throws CloneNotSupportedException {
    A a = null;
    try {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(baos);
        oos.writeObject(this);

        ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray());
        ObjectInputStream ois = new ObjectInputStream(bais);
        a = (A) ois.readObject();
    } catch (IOException e) {
        e.printStackTrace();
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    }
    
    return a;
}