一、浅拷贝与深拷贝
在Java中,对象拷贝可以分为浅拷贝和深拷贝。浅拷贝即拷贝对象的引用地址,使得指向同一块内存地址,而深拷贝则是在内存中重新申请一块与源对象完全相同的内存空间,使得复制对象和原始对象互不影响。
public class Person implements Cloneable { private String name; private int age; public Person(String name, int age) { this.name = name; this.age = age; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } @Override protected Object clone() throws CloneNotSupportedException { return super.clone(); } } public class Test { public static void main(String[] args) throws CloneNotSupportedException { // 浅拷贝 Person person1 = new Person("Tom", 18); Person person2 = person1; person1.setAge(20); System.out.println(person1.getAge()); //20 System.out.println(person2.getAge()); //20 // 深拷贝 Person person3 = new Person("Jerry", 22); Person person4 = (Person) person3.clone(); person3.setAge(25); System.out.println(person3.getAge()); //25 System.out.println(person4.getAge()); //22 } }
二、利用Cloneable接口实现浅拷贝
Java中的Cloneable接口提供了对象的浅拷贝机制,只需要在对象上实现Cloneable接口并重写Object类中的clone方法即可。需要注意的是,与Serializable不同,Cloneable并不是只是用为标识用,而是真正地在底层实现了对象的浅拷贝。
public class Person implements Cloneable { private String name; private int age; public Person(String name, int age) { this.name = name; this.age = age; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } @Override protected Object clone() throws CloneNotSupportedException { return super.clone(); } } public class Test { public static void main(String[] args) throws CloneNotSupportedException { Person person1 = new Person("Tom", 18); Person person2 = (Person) person1.clone(); person1.setAge(20); System.out.println(person1.getAge()); //20 System.out.println(person2.getAge()); //18 } }
三、利用序列化实现深拷贝
与浅拷贝不同的是,深拷贝需要重新申请一块完全相同的内存空间,在Java中,可以通过序列化来实现。
public class Person implements Serializable { private String name; private int age; public Person(String name, int age) { this.name = name; this.age = age; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public Person deepClone() throws IOException, ClassNotFoundException { ByteArrayOutputStream byteOut = new ByteArrayOutputStream(); ObjectOutputStream objOut = new ObjectOutputStream(byteOut); objOut.writeObject(this); ByteArrayInputStream byteIn = new ByteArrayInputStream(byteOut.toByteArray()); ObjectInputStream objIn = new ObjectInputStream(byteIn); return (Person) objIn.readObject(); } } public class Test { public static void main(String[] args) throws IOException, ClassNotFoundException { Person person1 = new Person("Tom", 18); Person person2 = person1.deepClone(); person1.setAge(20); System.out.println(person1.getAge()); //20 System.out.println(person2.getAge()); //18 } }
四、第三方库实现深拷贝
除了利用序列化之外,Java中也有一些第三方库可以方便地实现深拷贝。
public class Person { private String name; private int age; public Person(String name, int age) { this.name = name; this.age = age; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public staticT deepClone(T src) { return SerializationUtils.clone(src); } } public class Test { public static void main(String[] args) { Person person1 = new Person("Tom", 18); Person person2 = Person.deepClone(person1); person1.setAge(20); System.out.println(person1.getAge()); //20 System.out.println(person2.getAge()); //18 } }
五、结论
对象拷贝可以分为浅拷贝和深拷贝两种方式,浅拷贝不会创建新的对象实例,而是指向同一个对象实例;深拷贝会创建一个新的对象实例,并且将原对象中所有的属性都复制到新对象中。实现对象拷贝有多种方式,可以利用Cloneable接口和重写clone方法来实现浅拷贝,可以利用序列化来实现深拷贝,也可以使用第三方库来方便地实现深拷贝。