Java對象拷貝實現方法詳解

一、淺拷貝與深拷貝

在Java中，對象拷貝可以分為淺拷貝和深拷貝。淺拷貝即拷貝對象的引用地址，使得指向同一塊內存地址，而深拷貝則是在內存中重新申請一塊與源對象完全相同的內存空間，使得複製對象和原始對象互不影響。

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 {
        // 淺拷貝
        Person person1 = new Person("Tom", 18);
        Person person2 = person1;
        person1.setAge(20);
        System.out.println(person1.getAge());   //20
        System.out.println(person2.getAge());   //20

        // 深拷貝
        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介面實現淺拷貝

Java中的Cloneable介面提供了對象的淺拷貝機制，只需要在對象上實現Cloneable介面並重寫Object類中的clone方法即可。需要注意的是，與Serializable不同，Cloneable並不是只是用為標識用，而是真正地在底層實現了對象的淺拷貝。

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、利用序列化實現深拷貝

與淺拷貝不同的是，深拷貝需要重新申請一塊完全相同的內存空間，在Java中，可以通過序列化來實現。

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、第三方庫實現深拷貝

除了利用序列化之外，Java中也有一些第三方庫可以方便地實現深拷貝。

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 static  T 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、結論

對象拷貝可以分為淺拷貝和深拷貝兩種方式，淺拷貝不會創建新的對象實例，而是指向同一個對象實例；深拷貝會創建一個新的對象實例，並且將原對象中所有的屬性都複製到新對象中。實現對象拷貝有多種方式，可以利用Cloneable介面和重寫clone方法來實現淺拷貝，可以利用序列化來實現深拷貝，也可以使用第三方庫來方便地實現深拷貝。