java浅拷贝/深拷贝

 浅拷贝和深拷贝的定义

浅拷贝：只复制一个对象，对象内部存在的指向其他对象数组或者引用则不复制。

深拷贝：对象，对象内部的引用均复制。
为什么需要有对象拷贝？

有时候我们要获取到一个当前状态的对象复制品，他们是两个独立对象。不再是引用或者引用拷贝（实质都是指向对象本身）。就是说a是b的拷贝，b发生变化的时候，不要影响a。

对象拷贝有浅拷贝和深度拷贝两种

浅拷贝

浅拷贝是指对象中基本数据类型得到拷贝，而引用数据类型并未拷贝。
提到拷贝自然和clone联系起来了，所有具有clone功能的类都有一个特性，那就是它直接或间接地实现了Cloneable接口。
否则，我们在尝试调用clone（）方法时，将会触发CloneNotSupportedException异常。

eg:class DOG implements Cloneable {
 public DOG(String name, int age) {
  this.name = name;
  this.age = age;
 }
 public String getName() {
  return this.name;
 }
 public int getAge() {
  return this.age;
 }
 public Object clone() {
  try {
   return super.clone();
  } catch (CloneNotSupportedException e) {
   return null;
  }
 }
 public String name;
 private int age;
 // test
 public static void main(String[] args) {
  DOG dog1 = new DOG(" xiaogou ", 2);
  DOG dog2 = (DOG) dog1.clone();
  dog1.name = " dagou ";
  System.out.println(dog2.getName());
  System.out.println(dog2.getAge());
  System.out.println(dog1.getName());
  System.out.println(dog1.getAge());
 }

}

深度拷贝

相对浅拷贝。实现对象中基本数据类型和引用数据类型的拷贝

class AAA {  public AAA(String name) {   this.name = name;  }  public String name; } class DOG implements Cloneable {  public DOG(String name, int age, AAA birthday) {   this.name = name;   this.age = age;   this.birthday = birthday;  }  public String getName() {   return name;  }  public int getAge() {   return age;  }  public AAA getBirthday() {   return birthday;  }  public String getBirth(AAA a) {   return a.name;  }  public String name;  private int age;  public AAA birthday;  public Object clone() {   try {    super.clone();    return super.clone();   } catch (Exception e) {    return null;   }  } } public class TestClone {  public static void main(String[] args) {   AAA Day = new AAA(" test ");   DOG dog1 = new DOG(" xiaogou ", 2, Day);   DOG dog2 = (DOG) dog1.clone();   // dog2.birthday = (AAA) dog1.birthday.clone();   dog1.birthday.name = " 333 ";   System.out.println(dog1.getBirth(dog1.birthday));   System.out.println(dog2.getBirth(dog2.birthday));  } }

// 运行结果是：
// 333
// 333
// 而真正要实现拷贝还的加点代码，如下请对比上面和下面代码的异同之处

class AAA  implements  Cloneable{  public AAA(String name) {   this.name = name;  } public  Object clone()     {           try           {               super .clone();               return   super .clone();          }   catch  (Exception e)           {               return   null ;          }      }  public String name; } class DOG implements Cloneable {  public DOG(String name, int age, AAA birthday) {   this.name = name;   this.age = age;   this.birthday = birthday;  }  public String getName() {   return name;  }  public int getAge() {   return age;  }  public AAA getBirthday() {   return birthday;  }  public String getBirth(AAA a) {   return a.name;  }  public String name;  private int age;  public AAA birthday;  public Object clone() {   try {    super.clone();    return super.clone();   } catch (Exception e) {    return null;   }  } } public class TestClone {  public static void main(String[] args) {   AAA Day = new AAA(" test ");   DOG dog1 = new DOG(" xiaogou ", 2, Day);   DOG dog2 = (DOG) dog1.clone();   dog2.birthday  =  (AAA) dog1.birthday.clone(); // 特别注意这里   dog1.birthday.name = " 333 ";   System.out.println(dog1.getBirth(dog1.birthday));   System.out.println(dog2.getBirth(dog2.birthday));  } } 运行结果： 333 test 这样基本就达到了我们当初的目的

但是明显的这种方法还是有许多不足，人们总是希望一个clone就是对象直接克隆。而上面还要对对象中的对象递归使用clone。下面提供一种更高级点的做法

 序列化

class AAA implements Serializable {
	public AAA(String name) {
		this.name = name;
	}
	public String name;
}
class DOG extends SerialCloneable {
	public DOG(String name, int age, AAA birthday) {
		this.name = name;
		this.age = age;
		this.birthday = birthday;
	}
	public String getName() {
		return name;
	}
	public int getAge() {
		return age;
	}
	public AAA getBirthday() {
		return birthday;
	}
	public String getBirth(AAA a) {
		return a.name;
	}
	public String name;
	private int age;
	public AAA birthday;
	public Object clone() {
		try {
			super.clone();
			return super.clone();
		} catch (Exception e) {
			return null;
		}
	}
}
class TestClone {
	public static void main(String[] args) {
		AAA Day = new AAA(" test ");
		DOG dog1 = new DOG(" xiaogou ", 2, Day);
		DOG dog2 = (DOG) dog1.clone();
		// dog2.birthday = (AAA) dog1.birthday.clone();
		dog1.birthday.name = " 333 ";
		System.out.println(dog1.getBirth(dog1.birthday));
		System.out.println(dog2.getBirth(dog2.birthday));
	}
}
class SerialCloneable implements Cloneable, Serializable {
	public Object clone() {
		try {
			ByteArrayOutputStream bout = new ByteArrayOutputStream();
			ObjectOutputStream out = new ObjectOutputStream(bout);
			out.writeObject(this);
			out.close();
			ByteArrayInputStream bin = new ByteArrayInputStream(bout
					.toByteArray());
			ObjectInputStream in = new ObjectInputStream(bin);
			Object ret = in.readObject();
			in.close();
			return ret;
		} catch (Exception e) {
			return null;
		}
	}
}

// 输出：
// 333
// test

//这样也能够实现