浅拷贝
浅拷贝是按位拷贝对象，它会创建一个新对象，这个对象有着原始对象属性值的一份精确拷贝。如果属性是基本类型，拷贝的就是基本类型的值；如果属性是内存地址（引用类型），拷贝的就是内存地址，因此如果其中一个对象改变了这个地址，就会影响到另一个对象。
简而言之，浅拷贝仅仅复制锁考虑的对象，而不复制它所引用的对象。
实现浅拷贝的步骤是：
1、被复制的类需要实现Cloneable接口（不实现的话在调用clone方法会抛出CloneNotSupportedException异常）改接口为标记接口（不含任何方法）
2、覆盖clone()方法，访问修饰符设为public。方法中调用super.clone()方法得到需要的复制对象，(native为本地方法)
深拷贝
深拷贝还要吧一个对象中所引用的对象也要拷贝一遍。
下面是一个例子：
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package JavaCoreTechnology;
import java.io.Serializable;
/** * Created by benjamin on 1/14/16. */public class User implements Serializable, Cloneable { private static final long serialVersionUID = -3080870074068514966L;
private String userName; private Dog dog;
public String getUserName() { return userName; }
public void setUserName(String userName) { this.userName = userName; }
public Dog getDog() { return dog; }
public void setDog(Dog dog) { this.dog = dog; }
public User clone() throws CloneNotSupportedException { User user = (User)super.clone(); Dog d = dog.clone(); // 深拷贝必须克隆包含的对象 user.setDog(d); return user; }}
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package JavaCoreTechnology;
import java.io.Serializable;
/** * Created by benjamin on 1/14/16. */public class Dog implements Serializable, Cloneable { private static final long serialVersionUID = 8869944898908733919L;
private String dogName;
public String getDogName() { return dogName; }
public void setDogName(String dogName) { this.dogName = dogName; }
public Dog clone() throws CloneNotSupportedException { return (Dog)super.clone(); }}
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package JavaCoreTechnology;
/** * Created by benjamin on 1/14/16. */public class CloneTest {
public static void main(String[] args) throws CloneNotSupportedException { User user = new User(); Dog dog = new Dog(); dog.setDogName("D1"); user.setUserName("A1"); user.setDog(dog);
User user2 = user.clone(); user2.setUserName("A2"); user2.getDog().setDogName("D2");
System.out.println(user.getUserName()); // A1 System.out.println(user.getDog().getDogName()); // D1
System.out.println(user2.getUserName()); // A2 System.out.println(user2.getDog().getDogName()); // D2 }}
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可以发现上面已经成功的实现了深拷贝。但是试想一下，要是我一个类当中使用到了100个对象，那我也要一个个的去那些对象里面实现clone的方法吗，这显然有些太麻烦了。
为此，我们可以使用序列化对象的方法得到对象的一个拷贝。这就要用到了输入输出流。
修改一下代码，我们再来看一下：
去掉所有实体的Cloneable实现，以及clone方法：
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package JavaCoreTechnology;
import java.io.Serializable;
/** * Created by benjamin on 1/14/16. */public class User implements Serializable { private static final long serialVersionUID = -3080870074068514966L;
private String userName; private Dog dog;
public String getUserName() { return userName; }
public void setUserName(String userName) { this.userName = userName; }
public Dog getDog() { return dog; }
public void setDog(Dog dog) { this.dog = dog; }}
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package JavaCoreTechnology;
import java.io.Serializable;
/** * Created by benjamin on 1/14/16. */public class Dog implements Serializable { private static final long serialVersionUID = 8869944898908733919L;
private String dogName;
public String getDogName() { return dogName; }
public void setDogName(String dogName) { this.dogName = dogName; }}
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增加一个工具方法用来clone对象：
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package JavaCoreTechnology;
import java.io.ByteArrayInputStream;import java.io.ByteArrayOutputStream;import java.io.ObjectInputStream;import java.io.ObjectOutputStream;
/** * Created by benjamin on 1/14/16. */public class ObjCloner {
public static <T> T cloneObj(T obj) { T cloneVal = null;
try {
// 写入流中 ByteArrayOutputStream baos = new ByteArrayOutputStream(); ObjectOutputStream oos = new ObjectOutputStream(baos); oos.writeObject(obj);
// 从流中读入对象 ObjectInputStream ois = new ObjectInputStream(new ByteArrayInputStream(baos.toByteArray())); cloneVal = (T)ois.readObject();
} catch (Exception e) { e.printStackTrace(); }
return cloneVal; }}
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package JavaCoreTechnology;
/** * Created by benjamin on 1/14/16. */public class CloneTest {
public static void main(String[] args) throws CloneNotSupportedException { User user = new User(); Dog dog = new Dog(); dog.setDogName("D1"); user.setUserName("A1"); user.setDog(dog);
User user2 = ObjCloner.cloneObj(user); user2.setUserName("A2"); user2.getDog().setDogName("D2");
System.out.println(user.getUserName()); // A1 System.out.println(user.getDog().getDogName()); // D1
System.out.println(user2.getUserName()); // A2 System.out.println(user2.getDog().getDogName()); // D2 }}
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输出结果不变，总得看来，我更推荐大家使用流的方式来进行对象的深拷贝，不知道大家怎么看呢？
时间： 2024-10-31 21:30:06