Java之深淺拷貝

基本類型：拷貝數(shù)據(jù)的值
其他類型：拷貝地址的引用伍伤，拷貝出的新對(duì)象與原對(duì)象共享實(shí)例變量并徘，不受訪問(wèn)權(quán)限影響
String類型：拷貝的也是一個(gè)引用，但其內(nèi)容存儲(chǔ)在字符串池中扰魂，修改時(shí)會(huì)重新生成新的字符串麦乞，原有字符串內(nèi)容是保持不變的（String是不可變的），等同于基本類型劝评。

淺拷貝

淺拷貝就是直接使用"="給基本類型賦值（即使拷貝引用）

List<String> srcList = new ArrayList<>();
srcList.add("android");
List<String> cpyList = srcList;
srcList.add("ios");

輸出這兩個(gè)list姐直，srcList和cpyList都有android，ios兩項(xiàng)蒋畜。

深拷貝

深拷貝就是將所有屬性均拷貝到另外一個(gè)對(duì)象中声畏，將其中任何一個(gè)對(duì)象的任何一個(gè)屬性發(fā)生變化時(shí)，另外一個(gè)對(duì)象不受任何影響姻成。

List<String> srcList = new ArrayList<>();
srcList.add("android");
List<String> cpyList = new ArrayList<>(srcList);
srcList.add("ios");

輸出這兩個(gè)list插龄，srcList有android，ios兩項(xiàng)科展，而cpyList只有android一項(xiàng)均牢。

clone方法實(shí)現(xiàn)拷貝

每個(gè)對(duì)象都是繼承于Object類的，Object類提供了clone方法才睹，通過(guò)實(shí)現(xiàn)Cloneable接口可以使該具有拷貝的能力徘跪，拷貝的操作是在內(nèi)存中進(jìn)行中，所以性能會(huì)比直接構(gòu)造對(duì)象要快速很多琅攘。

public class Student implements Cloneable {
    private String name;
    private Teacher teacher;

    public String getName() {
        return name;
    }

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

    public Teacher getTeacher() {
        return teacher;
    }

    public void setTeacher(Teacher teacher) {
        this.teacher = teacher;
    }

    @Override
    protected Student clone() {
        Student s = null;
        try {
            s = (Student) super.clone();
            s.setTeacher(s.getTeacher());
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return s;
    }

    public static void main(String[] args) {
        Student s1 = new Student();
        s1.setName("Yao");
        s1.setTeacher(new Teacher("Kobe"));
        Student s2 = s1.clone();
        s2.setName("Yi");
        s2.getTeacher().setName("Jordan");
        System.out.println(s1.getName() + "'s teacher is "
                + s1.getTeacher().getName());
        System.out.println(s2.getName() + "'s teacher is "
                + s2.getTeacher().getName());

    }
}

class Teacher {
    private String name;

    public String getName() {
        return name;
    }

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

    public Teacher(String name) {
        super();
        this.name = name;
    }
}

輸出：
Yao's teacher is Jordan
Yi's teacher is Jordan
這里關(guān)于teacher的拷貝是通過(guò)"="號(hào)來(lái)操作的真椿，僅僅實(shí)現(xiàn)了淺拷貝。

@Override
protected Student clone() {
    Student s = null;
    try {
        s = (Student) super.clone();
        s.setTeacher(new Teacher(s.getTeacher().getName()));
    } catch (CloneNotSupportedException e) {
        e.printStackTrace();
    }
    return s;
}

將Student類的clone方法改成這樣即可實(shí)現(xiàn)深拷貝乎澄。
輸出：
Yao's teacher is Kobe
Yi's teacher is Jordan

通過(guò)對(duì)象序列化，使用writeObject和readObject也可以實(shí)現(xiàn)對(duì)象的深拷貝测摔。