Object類clone方法

Object中clone()方法是protected的，是淺拷貝，要使用clone方法，要重寫它，只有實現了implements Cloneable才可以調用該方法，否則會拋出CloneNotSupportedException異常。

@Override
    public Object clone(){
        Object o = null;
        try {
            o = super.clone();
        }catch (CloneNotSupportedException e){
            e.printStackTrace();
        }
//        Person p = (Person) o;
//        p.book = (Book)p.getBook().clone();              //放開這兩段即為深拷貝的用法
        return o;
    }

在我們需要復制對象的時候常用的三種方式

public static void main(String[] args){
    Book b = new Book("java");
    Person p = new Person("wt",b);
    Person p1 = new Person(p);
    Person p2 = (Person) p.clone();
    b.setBookName("js");
    p.setName("zjj");
    System.out.println("P:"+p);
    System.out.println("P1:"+p1);
    System.out.println("P2:"+p2);
}

當clone使用淺拷貝（即不放開那兩段）時，只拷貝對象不包含對對象引用的對象的拷貝：

P:{name:zjj, book:{bookName:js}}            
P1:{name:wt, book:{bookName:js}}      //不論是p1還是p2，基本類型的數值是直接拷貝值的，但是引用類型的對象卻是拷貝地址的
P2:{name:wt, book:{bookName:js}}      //這樣一旦p的原始值引用的對象改變，淺拷貝后的對象也會隨之變化

當clone使用深拷貝（即放開那兩段）時：

P2:{name:wt, book:{bookName:java}}      //深拷貝時，連對象中的對象都進行的是值拷貝，所以原始值的引用對象改變不會影響它

 

完整源代碼：

person類

public class Person implements Cloneable {
    private String name;
    private Book book;

    public Person(String name, Book book) {
        this.name = name;
        this.book = book;
    }

    public Person(Person p) {
        this.name = p.name;
        this.book = p.book;
    }

    @Override
    public Object clone(){
        Object o = null;
        try {
            o = super.clone();
        }catch (CloneNotSupportedException e){
            e.printStackTrace();
        }
        Person p = (Person) o;
        p.book = (Book)p.getBook().clone();
        return o;
    }

    public String getName() {
        return name;
    }

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

    public Book getBook() {
        return book;
    }

    public void setBook(Book book) {
        this.book = book;
    }

    @Override
    public String toString() {
        return "{name:" + name + ", book:" + book + "}";
    }
}

book類

public class Book implements Cloneable{
    private String bookName;
    public Book(String bookName) {
        this.bookName = bookName;
    }

    public String getBookName() {
        return bookName;
    }

    public void setBookName(String bookName) {
        this.bookName = bookName;
    }

    @Override
    public String toString() {
        return "{bookName:" + bookName + "}";
    }

    @Override
    public Object clone(){
        Object o = null;
        try {
            o = super.clone();
        }catch (CloneNotSupportedException e){
            e.printStackTrace();
        }
        return o;
    }
}

clone測試類

public class CloneTest {

    public static void main(String[] args){
        Book b = new Book("java");
        Person p = new Person("wt",b);
        Person p1 = new Person(p);
        Person p2 = (Person) p.clone();
        b.setBookName("js");
        p.setName("zjj");
        System.out.println("P:"+p);
        System.out.println("P1:"+p1);
        System.out.println("P2:"+p2);
    }
}