Java 对象拷贝

1.java拷贝对象有两种方式
a.使用java.lang.Object类中clone方法进行对象的拷贝
b.利用序列化进行对象的拷贝
2.利用Object的clone进行对象拷贝分为两种
a.浅拷贝：仅仅拷贝所考虑的对象，不拷贝引用的对象
b.深拷贝：不仅拷贝所考虑的对象，而且拷贝引用的对象
3.利用Object的clone进行对象拷贝，需要满足三个条件
a.类必须实现java.lang.Cloneable接口（否则拷贝对象时会抛出CloneNotSupportedException异常，不支持拷贝）
b.类必须重写clone方法,并声明为public（否则非子类不能调用clone方法进行拷贝）
c.类中clone方法中必须调用super.clone()
4.利用Object的clone方法进行深拷贝

//实现Cloneable接口
class Student implements Cloneable {
    String studentName;
    Teacher teacher;

    public Student(String studentName, Teacher teacher) {
        this.studentName = studentName;
        this.teacher = teacher;
    }

    // 重写Object的clone方法,并在方法中使用super.clone()
    @Override
    public Object clone() {
        // 拷贝Student类
        Student student = null;
        try {
            student = (Student) super.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return student;
    }
}

// 实现Cloneable接口
class Teacher implements Cloneable {
    String teacherName;

    public Teacher(String teacherName) {
        this.teacherName = teacherName;
    }

    // 重写Object的clone方法,并在方法中使用super.clone()
    @Override
    public Object clone() {
        Teacher teacher = null;
        try {
            teacher = (Teacher) super.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return teacher;
    }
}

public class CloneTest {
    public static void main(String[] args) throws CloneNotSupportedException {
        // 创建一个老师
        Teacher teacher = new Teacher("老师");
        // 创建一个学生，并且引用老师
        Student student1 = new Student("学生", teacher);
        // 拷贝一个学生
        Student student2 = (Student) student1.clone();
        // 检查学生是否同一个对象
        System.out.println("检查两个学生对象：" + (student1 == student2));
        // 检查老师是否同一个对象
        System.out.println("检查两个老师对象：" + (student2.teacher== teacher));
    }
}

打印结果为：
检查两个学生对象：false
检查两个老师对象：true
说明：只有学生对象被拷贝了，老师对象没有被拷贝，此拷贝方法为浅拷贝
5.利用Object的clone方法进行深拷贝

//实现Cloneable接口
class Student implements Cloneable {
    String studentName;
    Teacher teacher;

    public Student(String studentName, Teacher teacher) {
        this.studentName = studentName;
        this.teacher = teacher;
    }

    // 重写Object的clone方法,并在方法中使用super.clone()
    @Override
    public Object clone() {
        // 拷贝Student类
        Student student = null;
        try {
            student = (Student) super.clone();
            // 获取Student类中的Teacher类进行进行拷贝
            student.teacher =(Teacher) student.teacher.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return student;
    }
}

// 实现Cloneable接口
class Teacher implements Cloneable {
    String teacherName;

    public Teacher(String teacherName) {
        this.teacherName = teacherName;
    }

    // 重写Object的clone方法,并在方法中使用super.clone()
    @Override
    public Object clone() {
        Teacher teacher = null;
        try {
            teacher = (Teacher) super.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return teacher;
    }
}

public class CloneTest {
    public static void main(String[] args) throws CloneNotSupportedException {
        // 创建一个老师
        Teacher teacher = new Teacher("老师");
        // 创建一个学生，并且引用老师
        Student student1 = new Student("学生", teacher);
        // 拷贝一个学生
        Student student2 = (Student) student1.clone();
        // 检查学生是否同一个对象
        System.out.println("检查两个学生对象：" + (student1 == student2));
        // 检查老师是否同一个对象
        System.out.println("检查两个老师对象：" + (student2.teacher== teacher));
    }
}

打印结果为：
检查两个学生对象：false
检查两个老师对象：false
说明：学生和老师对象都被拷贝了，此拷贝方法为深拷贝
6.利用序列化（Serializable）实现拷贝对象
a.如需对序列化详细了解，请点击传送门
b.使用序列化拷贝对象

class Student implements Serializable {
    private static final long serialVersionUID = -5734927474270419167L;
    String studentName;
    Teacher teacher;

    public Student(String studentName, Teacher teacher) {
        this.studentName = studentName;
        this.teacher = teacher;
    }

}

// 实现Serializable接口
class Teacher implements Serializable {
    private static final long serialVersionUID = -8357235700226262125L;
    String teacherName;

    public Teacher(String teacherName) {
        this.teacherName = teacherName;
    }
}

public class CloneTest {
    public static void main(String[] args) throws Exception {
        // 创建一个老师
        Teacher teacher = new Teacher("老师");
        // 创建一个学生，并且引用老师
        Student student1 = new Student("学生", teacher);
        // 序列化
        FileOutputStream fos = new FileOutputStream("Student.txt");
        ObjectOutputStream oos = new ObjectOutputStream(fos);
        oos.writeObject(student1);
        // 反序列化
        FileInputStream fis = new FileInputStream("Student.txt");
        ObjectInputStream ois = new ObjectInputStream(fis);
        Student student2 = (Student) ois.readObject();
        // 检查学生是否同一个对象
        System.out.println("检查两个学生对象：" + (student1 == student2));
        // 检查老师是否同一个对象
        System.out.println("检查两个老师对象：" + (student2.teacher == teacher));
        oos.close();
        ois.close();
    }
}

打印结果为：
检查两个学生对象：false
检查两个老师对象：false
说明：使用序列化学生和老师对象都被拷贝了，此拷贝方法为深拷贝