关于 Cloneable 接口 和 重写 Object.clone() 方法的尝试顺便复习深拷贝和浅拷贝

一个类如果想重写 Object 的 clone 方法，则必须实现 Cloneable 接口，否则调用 clone 方法时将会抛出 CloneNotSupportException 异常

/**
 * Author:  heatdeath
 * Date:    2018/7/7
 * Desc:
 */
public class CloneDemo {
    static class CloneClass {
        public String str;

        @Override
        protected Object clone() throws CloneNotSupportedException {
            return super.clone();
        }
    }

    public static void main(String[] args) throws Exception {
        CloneClass cloneClass1 = new CloneClass();
        System.out.println(cloneClass1);
        cloneClass1.str = "hello world";

        CloneClass cloneClass2 = (CloneClass) cloneClass1.clone();
        System.out.println(cloneClass2);
        System.out.println(cloneClass2.str);
    }
}

com.heatdeath.test_package.CloneDemo$CloneClass@4554617c
Exception in thread "main" java.lang.CloneNotSupportedException: com.heatdeath.test_package.CloneDemo$CloneClass
    at java.lang.Object.clone(Native Method)
    at com.heatdeath.test_package.CloneDemo$CloneClass.clone(CloneDemo.java:14)
    at com.heatdeath.test_package.CloneDemo.main(CloneDemo.java:23)

---

正确的方式是，实现 Cloneable 接口，再重写 clone 方法（通常直接调用 super.clone() 方法，即 Object 类中受保护的 native clone 方法即可）

public class CloneDemo {
    static class CloneClass implements Cloneable {
        public String str;

        @Override
        protected Object clone() throws CloneNotSupportedException {
            return super.clone();
        }
    }


    public static void main(String[] args) throws Exception {
        CloneClass cloneClass1 = new CloneClass();
        System.out.println(cloneClass1);
        cloneClass1.str = "hello world";

        CloneClass cloneClass2 = (CloneClass) cloneClass1.clone();
        System.out.println(cloneClass2);
        System.out.println(cloneClass2.str);
    }
}

com.heatdeath.test_package.CloneDemo$CloneClass@4554617c
com.heatdeath.test_package.CloneDemo$CloneClass@74a14482
hello world

Process finished with exit code 0

---

再捎带着复习一下浅拷贝和深拷贝好了

浅拷贝 demo

public class CloneDemo {
    static class CloneClass implements Cloneable {
        public String str;
        public Hello helloRef;

        @Override
        protected Object clone() throws CloneNotSupportedException {
            return super.clone();
        }
    }

    static class Hello {
    }

    public static void main(String[] args) throws Exception {
        CloneClass cloneClass1 = new CloneClass();
        System.out.println(cloneClass1);
        cloneClass1.str = "hello world";
        cloneClass1.helloRef = new Hello();
        System.out.println(cloneClass1.helloRef);

        CloneClass cloneClass2 = (CloneClass) cloneClass1.clone();
        System.out.println(cloneClass2);
        System.out.println(cloneClass2.str);
        System.out.println(cloneClass2.helloRef);
    }
}

---

深拷贝

public class CloneDemo {
    static class CloneClass implements Cloneable {
        public String str;
        public Hello helloRef;

        @Override
        protected Object clone() throws CloneNotSupportedException {
            Object obj = super.clone();
            ((CloneClass) obj).helloRef = (Hello) helloRef.clone();
            return obj;
        }
    }

    static class Hello implements Cloneable {
        @Override
        protected Object clone() throws CloneNotSupportedException {
            return super.clone();
        }
    }

    public static void main(String[] args) throws Exception {
        CloneClass cloneClass1 = new CloneClass();
        System.out.println(cloneClass1);
        cloneClass1.str = "hello world";
        cloneClass1.helloRef = new Hello();
        System.out.println(cloneClass1.helloRef);

        CloneClass cloneClass2 = (CloneClass) cloneClass1.clone();
        System.out.println(cloneClass2);
        System.out.println(cloneClass2.str);
        System.out.println(cloneClass2.helloRef);
    }
}