//實(shí)體類(lèi)
public class Person{
    public String name;//姓名
    public int height;//身高
    public StringBuilder something;

    public String getName() {
        return name;
    }

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

    public int getHeight() {
        return height;
    }

    public void setHeight(int height) {
        this.height = height;
    }

    public StringBuilder getSomething() {
        return something;
    }

    public void setSomething(StringBuilder something) {
        this.something = something;
    }

    public Person(String name, int height, StringBuilder something) {
        this.name = name;
        this.height = height;
        this.something = something;
    }

}

//測(cè)試類(lèi)
public class copyTest {
    public static void main(String[] args) {
        Person p1 = new Person("小張", 180, new StringBuilder("今天天氣很好"));
        Person p2 = p1;

        System.out.println("對(duì)象是否相等："+ (p1 == p2));
        System.out.println("p1 屬性值=" + p1.getName()+ ","+ p1.getHeight() + ","+ p1.getSomething());
        System.out.println("p2 屬性值=" + p2.getName()+ ","+ p2.getHeight() + ","+ p2.getSomething());


        // change
        p1.name="小王";
        p1.height = 200;
        p1.something.append(",適合出去玩");
        System.out.println("...after p1 change....");

        System.out.println("p1 屬性值=" + p1.getName()+ ","+ p1.getHeight() + ","+ p1.getSomething());
        System.out.println("p2 屬性值=" + p2.getName()+ ","+ p2.getHeight() + ","+ p2.getSomething());

    }
}

結(jié)果：

對(duì)象是否相等：true
p1 屬性值=小張,180,今天天氣很好
p2 屬性值=小張,180,今天天氣很好
...after p1 change....
p1 屬性值=小王,200,今天天氣很好,適合出去玩
p2 屬性值=小王,200,今天天氣很好,適合出去玩

before change:

after change:

我們可以看出由于2個(gè)引用p1,p2 都是指向堆中同一個(gè)對(duì)象，所以2個(gè)對(duì)象是相等的，修改了對(duì)象p1，會(huì)影響到對(duì)象p2
需要注意的

name屬性，雖然她是引用類(lèi)型，但她同時(shí)也是String類(lèi)型，不可變，對(duì)其修改，JVM會(huì)默認(rèn)在堆上創(chuàng)建新的內(nèi)存空間，再重新賦值
int weight=180; 是成員變量，存放在堆中，不是所有的基本類(lèi)型變量都存放在JVM棧中

注意與這篇文章得區(qū)分開(kāi)來(lái)， int num1 = 10;是基本類(lèi)型的局部變量，存放在棧中

淺拷貝

淺拷貝：淺拷貝會(huì)在堆上創(chuàng)建一個(gè)新的對(duì)象，新對(duì)象和原對(duì)象不等，但是新對(duì)象的屬性和老對(duì)象相同。

其中：

如果屬性是基本類(lèi)型(int,double,long,boolean等)，拷貝的就是基本類(lèi)型的值。
如果屬性是引用類(lèi)型(除了基本類(lèi)型都是引用類(lèi)型)，拷貝的就是引?數(shù)據(jù)類(lèi)型變量的地址值，?對(duì)于引?類(lèi)型變量指向的堆中的對(duì)象不會(huì)拷貝。

如何實(shí)現(xiàn)淺拷貝呢？也很簡(jiǎn)單，就是在需要拷貝的類(lèi)上實(shí)現(xiàn)Cloneable接口并重寫(xiě)其clone()方法。

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

在使用的時(shí)候直接調(diào)用類(lèi)的clone()方法即可

//實(shí)體類(lèi) 繼承Cloneable
public class Person implements Cloneable{
    public String name;//姓名
    public int height;//身高
    public StringBuilder something;

    public String getName() {
        return name;
    }

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

    public int getHeight() {
        return height;
    }

    public void setHeight(int height) {
        this.height = height;
    }

    public StringBuilder getSomething() {
        return something;
    }

    public void setSomething(StringBuilder something) {
        this.something = something;
    }

    public Person(String name, int height, StringBuilder something) {
        this.name = name;
        this.height = height;
        this.something = something;
    }



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

}

//測(cè)試類(lèi)
public class shallowCopyTest {

    public static void main(String[] args) throws CloneNotSupportedException {
        Person p1 = new Person("小張", 180, new StringBuilder("今天天氣很好"));
        Person p2 = p1.clone();

        System.out.println("對(duì)象是否相等："+ (p1 == p2));
        System.out.println("p1 屬性值=" + p1.getName()+ ","+ p1.getHeight() + ","+ p1.getSomething());
        System.out.println("p2 屬性值=" + p2.getName()+ ","+ p2.getHeight() + ","+ p2.getSomething());


        // change
        p1.setName("小王");
        p1.setHeight(200);
        p1.getSomething().append(",適合出去玩");
        System.out.println("...after p1 change....");

        System.out.println("p1 屬性值=" + p1.getName()+ ","+ p1.getHeight() + ","+ p1.getSomething());
        System.out.println("p2 屬性值=" + p2.getName()+ ","+ p2.getHeight() + ","+ p2.getSomething());

    }
}

結(jié)果：

對(duì)象是否相等：false
p1 屬性值=小張,180,今天天氣很好
p2 屬性值=小張,180,今天天氣很好
...after p1 change....
p1 屬性值=小王,200,今天天氣很好,適合出去玩
p2 屬性值=小張,180,今天天氣很好,適合出去玩

before change:

after change:

我們可以看出：

當(dāng)我們修改對(duì)象p1的weight屬性時(shí)，由于p2的height屬性是直接復(fù)制修改前的p1的height屬性，所以還是180。
當(dāng)我們修改對(duì)象p1的name屬性時(shí)，String name指向一個(gè)新的內(nèi)存空間，但對(duì)象p2的name還是指向舊的內(nèi)存空間，所以對(duì)象p2的name屬性還是"小張"。
由于對(duì)象p1的something屬性和對(duì)象p2的something屬性指向是同一個(gè)內(nèi)存空間，當(dāng)我們修改對(duì)象p1的something屬性，會(huì)影響到對(duì)象p2的something屬性，所以對(duì)象p2的something屬性變?yōu)?quot;今天天氣很好,適合出去玩"。

深拷貝

深拷貝：完全拷貝?個(gè)對(duì)象，在堆上創(chuàng)建一個(gè)新的對(duì)象，拷貝被拷貝對(duì)象的成員變量的值，同時(shí)堆中的對(duì)象也會(huì)拷貝。
需要重寫(xiě)clone方法

    @Override
    public Person clone() throws CloneNotSupportedException {
        //return (Person) super.clone();
        Person person = (Person) super.clone();
        person.setSomething( new StringBuilder(person.getSomething()));//單獨(dú)為引用類(lèi)型clone
        return person;
    }

shallowCopyTest測(cè)試類(lèi)的結(jié)果：

對(duì)象是否相等：false
p1 屬性值=小張,180,今天天氣很好
p2 屬性值=小張,180,今天天氣很好
...after p1 change....
p1 屬性值=小王,200,今天天氣很好,適合出去玩
p2 屬性值=小張,180,今天天氣很好

這時(shí)候?qū)ο髉1和對(duì)象p2互不干擾了

before change:

after change:

但這樣也有個(gè)小問(wèn)題，對(duì)象每有一個(gè)引用類(lèi)型，我們都得重寫(xiě)其clone方法，這樣會(huì)非常麻煩，因此我們還可以借助序列化來(lái)實(shí)現(xiàn)對(duì)象的深拷貝

//實(shí)體類(lèi) 繼承Cloneable
public class Person implements Serializable{
    public String name;//姓名
    public int height;//身高
    public StringBuilder something;

...//省略 getter setter


    public Object deepClone() throws Exception{
        // 序列化
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(bos);
    
        oos.writeObject(this);
    
        // 反序列化
        ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());
        ObjectInputStream ois = new ObjectInputStream(bis);
    
        return ois.readObject();
    }

}

//測(cè)試類(lèi)，這邊類(lèi)名筆者就不換了，在之前的基礎(chǔ)上改改
public class shallowCopyTest {

    public static void main(String[] args) throws Exception {
        Person p1 = new Person("小張", 180, new StringBuilder("今天天氣很好"));
        Person p2 = (Person)p1.deepClone();

        System.out.println("對(duì)象是否相等："+ (p1 == p2));
        System.out.println("p1 屬性值=" + p1.getName()+ ","+ p1.getHeight() + ","+ p1.getSomething());
        System.out.println("p2 屬性值=" + p2.getName()+ ","+ p2.getHeight() + ","+ p2.getSomething());


        // change
        p1.setName("小王");
        p1.setHeight(200);
        p1.getSomething().append(",適合出去玩");
        System.out.println("...after p1 change....");

        System.out.println("p1 屬性值=" + p1.getName()+ ","+ p1.getHeight() + ","+ p1.getSomething());
        System.out.println("p2 屬性值=" + p2.getName()+ ","+ p2.getHeight() + ","+ p2.getSomething());

    }
}

這樣也會(huì)得到深拷貝的結(jié)果