java基礎學習-克隆

淺複製

被複制對象的所有變量都含有與原來的對象相同的值，而所有的對其他對象的引用仍然指向原來的對象。換言之，淺複製僅僅複製所考慮的對象，而不復制它所引用的對象。

深複製

被複制對象的所有變量都含有與原來的對象相同的值，除去那些引用其他對象的變量。那些引用其他對象的變量將指向被複制過的新對象，而不再是原有的那些被引用的對象。換言之，深複製把要複製的對象所引用的對象都複製了一遍（遞歸下去）。

Java中對象的克隆

Object的clone()方法

clone方法將對象複製了一份並返回給調用者。
一般而言，clone（）方法滿足：
1）對任何的對象x，都有x.clone() !=x
克隆對象與原對象不是同一個對象
2）對任何的對象x，都有x.clone().getClass()= =x.getClass()
克隆對象與原對象的類型一樣
3）如果對象x的equals()方法定義恰當，那麼x.clone().equals(x)應該成立。

實現：

1）爲了獲取對象的一份拷貝，我們可以利用Object類的clone()方法。
2）在派生類中覆蓋基類的clone()方法，並聲明爲public（Object類中的clone()方法爲protected的）
3）在派生類的clone()方法中，調用super.clone()
4）在派生類中實現Cloneable接口

淺複製

public class Student implements Cloneable {
	private int age;
	private String name;
	private Book book;

	public int getAge() {
		return age;
	}

	public Book getBook() {
		return book;
	}

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

	public void setAge(int age) {
		this.age = age;
	}

	public String getName() {
		return name;
	}

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

	@Override
	public Object clone() throws CloneNotSupportedException {
		Object object = super.clone();
		return object;
	}

}

public class Book {
	
	public String name;

	public String getName() {
		return name;
	}

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

public class Test {
	public static void main(String[] args) throws CloneNotSupportedException {
		Student student1 = new Student();
		Book book = new Book();
		book.setName("english");
		student1.setName("zhangsan");
		student1.setAge(22);
		student1.setBook(book);
		Student student2 = (Student) student1.clone();
		System.out.println(student1.clone().equals(student1));// false
		System.out.println(student1.clone() == student1);// false
		System.out.println(student1.clone().getClass() == student2.getClass());// true
		System.out.println(student2.getName());// zhangsan
		student1.setName("lisi");
		student1.getBook().setName("chinese");
		System.out.println(student2.getName());// zhangsan
		System.out.println(student2.getBook().getName());// chinese
	}
}

深複製

方式一：利用clone方法

public class Fruit implements Cloneable {

	public String name;

	public Apple apple;

	public String getName() {
		return name;
	}

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

	public Apple getApple() {
		return apple;
	}

	public void setApple(Apple apple) {
		this.apple = apple;
	}

	@Override
	public Object clone() throws CloneNotSupportedException {
		<strong>Fruit fruit1 = (Fruit) super.clone();
		fruit1.setApple((Apple) fruit1.getApple().clone());
		return fruit1;</strong>
	}
}

public class Apple  implements Cloneable {

	public String Name = "";

	public String getName() {
		return Name;
	}

	public void setName(String name) {
		Name = name;
	}

	@Override
	public Object clone() throws CloneNotSupportedException {
		<strong>return super.clone();</strong>
	}
}

public class Test {
	public static void main(String[] args) throws Exception {

		Fruit fruit1 = new Fruit();
		Apple apple = new Apple();
		fruit1.setName("apple");
		apple.setName("fusi");
		fruit1.setApple(apple);
		Fruit fruit2 = (Fruit) fruit1.clone();
		System.out.println(fruit1.clone().equals(fruit1));// false
		System.out.println(fruit1.clone() == fruit1);// false
		System.out.println(fruit1.clone().getClass() == fruit2.getClass());// true
		System.out.println(fruit2.getName());// apple
		fruit1.setName("banana");
		fruit1.getApple().setName("shandong");
		System.out.println(fruit2.getName());// apple
		System.out.println(fruit2.getApple().getName());// fusi
		
	}
}

方式二：序列化方式

public class People  implements Serializable {

	public String name;
	
	public Girl girl;

	public String getName() {
		return name;
	}

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

	public Girl getGirl() {
		return girl;
	}

	public void setGirl(Girl girl) {
		this.girl = girl;
	}
	
	public Object deepCopy() throws Exception{
		ByteArrayOutputStream bos = new ByteArrayOutputStream();		
		ObjectOutputStream oos = new ObjectOutputStream(bos);		
		oos.writeObject(this);		
		ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());		
		ObjectInputStream ois = new ObjectInputStream(bis);		
		return ois.readObject();
	}
}

public class Girl  implements Serializable {

	public String name;

	public String getName() {
		return name;
	}

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

public class Test {
	public static void main(String[] args) throws Exception {
		
		People people1 = new People();
		Girl girl = new Girl();
		people1.setName("zhangsan");
		girl.setName("meimei");
		people1.setGirl(girl);
		People people2 = (People) people1.deepCopy();
		System.out.println(people1.deepCopy().equals(people1));// false
		System.out.println(people1.deepCopy() == people1);// false
		System.out.println(people1.deepCopy().getClass() == people2.getClass());// true
		System.out.println(people2.getName());// zhangsan
		people1.setName("lisi");
		people1.getGirl().setName("lili");
		System.out.println(people2.getName());// zhangsan
		System.out.println(people2.getGirl().getName());// meimei
	}
}