浅拷贝深拷贝2

// Cloneable 接口是一个标记接口，用来表示某个功能在执行的时候是合法的
public interface Cloneable {
}

没有引用类型字段时

class Writer implements Cloneable {
    private int age;
    private String name;
 
    // get,set和构造函数
 
    @Override
    public String toString() {
        return "Writer{" +
                "age=" + age +
                ", name='" + name + '\'' +
                '}';
    }
 
    @Override
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
}

• 如果一个类没有实现 Cloneable 接口，即便它重写了 clone() 方法，依然是无法调用该方法进行对象克隆的，程序在执行 clone() 方法的时候会抛出 CloneNotSupportedException 异常

public static void main(String[] args) throws CloneNotSupportedException {
    Writer writer1 = new Writer(18, "二狗");
    Writer writer2 = (Writer) writer1.clone();
 
    System.out.println("浅拷贝后：");
    System.out.println("writer1：" + writer1);
    System.out.println("writer2：" + writer2);
 
    writer2.setName("铁蛋");
 
    System.out.println("调整了 writer2 的 name 后：");
    System.out.println("writer1：" + writer1);
    System.out.println("writer2：" + writer2);
    /*
        浅拷贝后：
        writer1：Writer{age=18, name='二狗'}
        writer2：Writer{age=18, name='二狗'}
        调整了 writer2 的 name 后：
        writer1：Writer{age=18, name='二狗'}
        writer2：Writer{age=18, name='铁蛋'}
     */
}

• 字符串 String 是不可变对象，一个新的值必须在字符串常量池中开辟一段新的内存空间，所以并没有影响到字符串二狗的值

有引用类型字段时

浅拷贝

class Book {
    private String bookName;
    private int price;
 
    // get,set和构造函数
 
    @Override
    public String toString() {
        return super.toString().substring(26) +
                " bookName='" + bookName + '\'' +
                ", price=" + price +
                '}';
    }
}
 
class Writer implements Cloneable {
    private int age;
    private String name;
    // 新加了个自定义的引用类型字段
    private Book book;
 
   	// get,set和构造函数
 
    @Override
    public String toString() {
        return "Writer{" +
                "age=" + age +
                ", name='" + name + '\'' +
                ", book=" + book +
                '}';
    }
 
    @Override
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
}

public static void main(String[] args) throws CloneNotSupportedException {
    Writer writer1 = new Writer(18,"二狗",new Book("编译原理",100));
    Writer writer2 = (Writer) writer1.clone();
 
    System.out.println("浅拷贝后：");
    System.out.println("writer1：" + writer1);
    System.out.println("writer2：" + writer2);
 
    Book book = writer2.getBook();
    book.setBookName("离散数学");
    book.setPrice(70);
 
    System.out.println("writer2.book 变更后：");
    System.out.println("writer1：" + writer1);
    System.out.println("writer2：" + writer2);
 
    /*
        浅拷贝后：
        writer1：Writer{age=18, name='二狗', book=86 bookName='编译原理', price=100}}
        writer2：Writer{age=18, name='二狗', book=86 bookName='编译原理', price=100}}
        writer2.book 变更后：
        writer1：Writer{age=18, name='二狗', book=86 bookName='离散数学', price=70}}
        writer2：Writer{age=18, name='二狗', book=86 bookName='离散数学', price=70}}
     */
}

• writer2.book 变更后，writer1.book 也发生了改变。自定义对象的内存地址并没有发生改变，只是对应的字段值发生了改变

• 浅拷贝克隆的对象中，引用类型的字段指向的是同一个，当改变任何一个对象，另外一个对象也会随之改变，除去字符串的特殊性外

深拷贝

• 深拷贝和浅拷贝不同的，深拷贝中的引用类型字段也会克隆一份，当改变任何一个对象，另外一个对象不会随之改变

class Book implements Cloneable{
    private String bookName;
    private int price;
 
    // get,set和构造函数
 
    @Override
    public String toString() {
        return super.toString().substring(26) +
                " bookName='" + bookName + '\'' +
                ", price=" + price +
                '}';
    }
 
    // 重写了 clone() 方法，并实现了 Cloneable 接口。为的就是深拷贝的时候也能够克隆该字段。
    @Override
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
}

class Writer implements Cloneable {
    private int age;
    private String name;
    private Book book;
 
    // get,set和构造函数
 
    @Override
    public String toString() {
        return "Writer{" +
                "age=" + age +
                ", name='" + name + '\'' +
                ", book=" + book +
                '}';
    }
 
    @Override
    protected Object clone() throws CloneNotSupportedException {
        // 不再只调用 Object 的 clone() 方法对 Writer 进行克隆了
        Writer writer = (Writer) super.clone();
        // 还对 Book 也进行了克隆
        writer.setBook((Book) writer.getBook().clone());
        return writer;
    }
}

public static void main(String[] args) throws CloneNotSupportedException {
    Writer writer1 = new Writer(18,"二狗",new Book("编译原理",100));
    Writer writer2 = (Writer) writer1.clone();
 
    System.out.println("深拷贝后：");
    System.out.println("writer1：" + writer1);
    System.out.println("writer2：" + writer2);
 
    Book book = writer2.getBook();
    book.setBookName("离散数学");
    book.setPrice(70);
 
    System.out.println("writer2.book 变更后：");
    System.out.println("writer1：" + writer1);
    System.out.println("writer2：" + writer2);
 
    /*
        深拷贝后：
        writer1：Writer{age=18, name='二狗', book=86 bookName='编译原理', price=100}}
        writer2：Writer{age=18, name='二狗', book=86 bookName='编译原理', price=100}}
        writer2.book 变更后：
        writer1：Writer{age=18, name='二狗', book=86 bookName='离散数学', price=100}}
        writer2：Writer{age=18, name='二狗', book=86 bookName='离散数学', price=70}}
     */
}

• 通过 clone() 方法实现的深拷贝比较笨重，因为要将所有的引用类型都重写 clone() 方法

使用序列化实现深拷贝

class Book implements Serializable {
    private String bookName;
    private int price;
	...
}

class Writer implements Serializable {
    private int age;
    private String name;
    private Book book;
 
	...
 
    //深度拷贝
    public Object deepClone() throws IOException, ClassNotFoundException {
        // 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();
    }
}

public static void main(String[] args) throws IOException, ClassNotFoundException {
    Writer writer1 = new Writer(18, "二狗", new Book("编译原理", 100));
    Writer writer2 = (Writer) writer1.deepClone();
 
    System.out.println("深拷贝后：");
    System.out.println("writer1：" + writer1);
    System.out.println("writer2：" + writer2);
 
    Book book = writer2.getBook();
    book.setBookName("离散数学");
    book.setPrice(70);
 
    System.out.println("writer2.book 变更后：");
    System.out.println("writer1：" + writer1);
    System.out.println("writer2：" + writer2);
 
    /*
        深拷贝后：
        writer1：Writer{age=18, name='二狗', book=86 bookName='编译原理', price=100}}
        writer2：Writer{age=18, name='二狗', book=86 bookName='编译原理', price=100}}
        writer2.book 变更后：
        writer1：Writer{age=18, name='二狗', book=86 bookName='离散数学', price=100}}
        writer2：Writer{age=18, name='二狗', book=86 bookName='离散数学', price=70}}
     */
}