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浅拷贝

浅拷贝会创建一个新的对象，复制该对象的基本类型引用，但不复制该对象内的其他对象引用。一个对象要支持浅拷贝，需要实现Cloneable接口，不然在调用clone()方法时会抛出异常

    protected Object clone() throws CloneNotSupportedException {if (!(this instanceof Cloneable)) {throw new CloneNotSupportedException("Class " + getClass().getName() +" doesn't implement Cloneable");}return internalClone();}

看个简单的demo

public class ShallowCopy implements Cloneable {int i = 10;String str = "ShallowCopy";Shallow shallow = new Shallow();public static class Shallow {String shallow = "shallow";}public static void testShallowCopy() {ShallowCopy shallowCopy = new ShallowCopy();try {ShallowCopy shallowCopyClone = (ShallowCopy) shallowCopy.clone();LogUtil.info("ShallowCopy", "(shallowCopy == shallowCopyClone) = " + (shallowCopy == shallowCopyClone));LogUtil.info("ShallowCopy", "(shallowCopy.equals(shallowCopyClone)) = " + (shallowCopy.equals(shallowCopyClone)));LogUtil.info("ShallowCopy", "(shallowCopy.shallow == shallowCopyClone.shallow) = " + (shallowCopy.shallow == shallowCopyClone.shallow));LogUtil.info("ShallowCopy", "(shallowCopy.shallow.equals(shallowCopyClone.shallow)) = " + (shallowCopy.shallow.equals(shallowCopyClone.shallow)));} catch (CloneNotSupportedException e) {throw new RuntimeException(e);}}
}

打印结果如下

2025-03-13 16:53:25.564   (shallowCopy == shallowCopyClone) = false
2025-03-13 16:53:25.564   (shallowCopy.equals(shallowCopyClone)) = false
2025-03-13 16:53:25.564   (shallowCopy.shallow == shallowCopyClone.shallow) = true
2025-03-13 16:53:25.564   (shallowCopy.shallow.equals(shallowCopyClone.shallow)) = true

我们发现shallowCopy和shallowCopyClone指向不同的对象，但是里面的shallow却是同一个。如果要实现两个shallowCopy和shallowCopyClone两个完全不同的对象，也即是要实现深拷贝，有两个办法，下文介绍两种方法

深拷贝

1. 内部的对象引用所属类也继承clone接口，重写clone()方法，例如

public class ShallowCopy implements Cloneable {int i = 10;String str = "ShallowCopy";Shallow shallow = new Shallow();@NonNull@Overrideprotected Object clone() throws CloneNotSupportedException {ShallowCopy cloned = (ShallowCopy)super.clone();cloned.shallow = (Shallow)shallow.clone();return cloned;}public static class Shallow implements Cloneable {String shallow = "shallow";@NonNull@Overrideprotected Object clone() throws CloneNotSupportedException {return super.clone();}}public static void testShallowCopy() {ShallowCopy shallowCopy = new ShallowCopy();try {ShallowCopy shallowCopyClone = (ShallowCopy) shallowCopy.clone();LogUtil.info("ShallowCopy", "(shallowCopy == shallowCopyClone) = " + (shallowCopy == shallowCopyClone)); // falseLogUtil.info("ShallowCopy", "(shallowCopy.equals(shallowCopyClone)) = " + (shallowCopy.equals(shallowCopyClone))); // falseLogUtil.info("ShallowCopy", "(shallowCopy.shallow == shallowCopyClone.shallow) = " + (shallowCopy.shallow == shallowCopyClone.shallow)); // falseLogUtil.info("ShallowCopy", "(shallowCopy.shallow.equals(shallowCopyClone.shallow)) = " + (shallowCopy.shallow.equals(shallowCopyClone.shallow))); // false} catch (CloneNotSupportedException e) {throw new RuntimeException(e);}}
}

返回结果

2025-03-13 17:14:09.906   (shallowCopy == shallowCopyClone) = false
2025-03-13 17:14:09.906   (shallowCopy.equals(shallowCopyClone)) = false
2025-03-13 17:14:09.906   (shallowCopy.shallow == shallowCopyClone.shallow) = false
2025-03-13 17:14:09.906   (shallowCopy.shallow.equals(shallowCopyClone.shallow)) = false

但这个方法有个弊端，就是如果引用对象的链路比较深，例如 A 引用 B，B 引用 C，C 引用 D，甚至更深，就需要重写很多clone()方法，不易于维护.

值得注意的是Shallow类里面的shallow变量，它是一个String类型的对象引用，但是却可以不用实现clone接口实现深拷贝。原因是String是不可变的，修改String类型都会返回一个新对象，参考文档String 基础知识

2. 使用Serializable序列化实现深拷贝

需要注意的是引用对象的类型也要实现Serializable接口，不然后报错

public class ShallowCopy implements Cloneable, Serializable {public static class Shallow implements Cloneable, Serializable {}
}

如果Shallow没有实现Serializable接口，则会出现java.io.NotSerializableException。接着使用IO实现序列化和反序列化

    public ShallowCopy deepClone() {ShallowCopy deepClone = null;try {ByteArrayOutputStream bos = new ByteArrayOutputStream();ObjectOutputStream oos = new ObjectOutputStream(bos);oos.writeObject(this);ByteArrayInputStream bio = new ByteArrayInputStream(bos.toByteArray());ObjectInputStream ois = new ObjectInputStream(bio);deepClone = (ShallowCopy) ois.readObject();} catch (IOException | ClassNotFoundException e) {throw new RuntimeException(e);}return deepClone;}

结果打印

    public static void testDeepCopy() {ShallowCopy shallowCopy = new ShallowCopy();ShallowCopy shallowCopyDeepClone = shallowCopy.deepClone();LogUtil.info("ShallowCopy", "(shallowCopy == shallowCopyDeepClone) = " + (shallowCopy == shallowCopyDeepClone)); // falseLogUtil.info("ShallowCopy", "(shallowCopy.equals(shallowCopyDeepClone)) = " + (shallowCopy.equals(shallowCopyDeepClone))); // falseLogUtil.info("ShallowCopy", "(shallowCopy.shallow == shallowCopyDeepClone.shallow) = " + (shallowCopy.shallow == shallowCopyDeepClone.shallow)); // falseLogUtil.info("ShallowCopy", "(shallowCopy.shallow.equals(shallowCopyDeepClone.shallow)) = " + (shallowCopy.shallow.equals(shallowCopyDeepClone.shallow))); // false}