深拷贝（deep clone）与浅拷贝(shallow clone)
浅复制（浅克隆）：被复制对象的所有变量都含有与原来对象相同的值，而所有的对其他对象的引用仍然指向原来的对象。换言之，浅复制仅仅复制所考虑的对象，而不复制它所引用的对象。
深复制（深克隆）：被复制对象的所有变量都含有与原来对象相同的值，除去那些引用其他对象的变量。那些引用其他对象的变量将指向被复制的新对象，而不再是原有的那些被引用的对象。换言之，深复制把复制的对象所引用的对象都复制了一遍。
Object的clone()方法
将对象复制一份并返回给调用者。
一般而言，clone方法满足：
1.对任何的x,都有
x.clone() != x
克隆对象与原对象不是同个对象。
2.对任何的对象x,都有
x.clone().getClass() == x.getClass()
克隆对象与原对象的类型一样
3.如果x的equals方法定义恰当中，那么
x.clone().equals(x)
应该成立。
浅复制示例
|
public class ColneTest { public static void main(String[] args) throws Throwable { Student s1 = new Student(); s1.setAge(20); s1.setName("jack"); Student s2 = (Student)s1.clone(); System.out.println(s2.getAge()); System.out.println(s2.getName()); System.out.println("--------------------------"); s2.setName("bob"); System.out.println(s1.getName()); System.out.println(s2.getName()); } } class Student implements Cloneable { private int age; private String Name ; public int getAge() { return age; } public void setAge(int age) { this.age = age; } public String getName() { return Name; } public void setName(String name) { Name = name; } @Override public Object clone() throws
CloneNotSupportedException { Object obj = super.clone(); return obj; } } |
|
public class CloneTest2 { public static void main(String[] args) throws Throwable { Teacher t1 = new Teacher(); t1.setAge(40); t1.setName("Teacher Li"); Student2 s1 = new Student2(); s1.setAge(20); s1.setName("Bob"); s1.setTeacher(t1); Student2 s2 = (Student2) s1.clone(); System.out.println(s2.getAge()); System.out.println(s2.getName()); s1.getTeacher().setName("Teacher Zhang"); System.out.println(s2.getTeacher().getAge()); System.out.println(s2.getTeacher().getName()); } } class Teacher implements Cloneable { private int age; private String name; public int getAge() { return age; } public void setAge(int age) { this.age = age; } public String getName() { return name; } public void setName(String name) { this.name = name; } @Override protected Object clone() throws
CloneNotSupportedException { return super.clone(); } } class Student2 implements Cloneable { private int age; private String name; private Teacher teacher;//浅拷贝没有复制这个对象的引用，深拷贝复制了这个对象的引用。 public int getAge() { return age; } public void setAge(int age) { this.age = age; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Teacher getTeacher() { return teacher; } public void setTeacher(Teacher teacher) { this.teacher = teacher; } @Override protected Object clone() throws
CloneNotSupportedException { //手动深复制 Student2 stu = (Student2) super.clone(); stu.setTeacher((Teacher) stu.getTeacher().clone()); return stu; } } |
利用序列化来做觉深复制
把对象写到流里的过程是序列化（Serilization）过程，而把对象从流中读出来的过程则叫做反序列化（Deserialization）过程。应当指出的是，写在流里的是对象的一个拷贝，而对象仍然存在于JVM里面。
|
public class CloneTest3 { public static void main(String[] args) throws Exception { Teacher3 t1 = new Teacher3(); t1.setAge(40); t1.setName("Teacher Li"); Student3 s1 = new Student3(); s1.setAge(20); s1.setName("Jack"); s1.setTeacher(t1); Student3 s2 = (Student3)s1.deepCopy(); System.out.println(s2.getAge()); System.out.println(s2.getName()); s1.getTeacher().setName("Teacher Wang"); System.out.println(s2.getTeacher().getAge()); System.out.println(s2.getTeacher().getName()); } } //必须要实现Serializable接口 class Teacher3 implements Serializable { private int age ; private String name; public int getAge() { return age; } public void setAge(int age) { this.age = age; } public String getName() { return name; } public void setName(String name) { this.name = name; } } //必须要实现Serializable接口，这个接口是个标识接口，没有定义任何方法 class Student3 implements Serializable { private int age; private String name; private Teacher3 teacher; public int getAge() { return age; } public void setAge(int age) { this.age = age; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Teacher3 getTeacher() { return teacher; } public void setTeacher(Teacher3 teacher) { this.teacher = teacher; } //用序列化的特点来进行深拷贝。无论有多少个对象引用都可以复制 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(); } } |
