Java 如何复制对象（不是复制引用）

Java code

public class CloneTest {    public static void main(String[] args) {        A a = new A();        A b = new A(3);        System.out.println(a.i);        System.out.println(b.i);        a = b.clone();        System.out.println(a.i);        b.i = 5;        System.out.println(b.i);        System.out.println(a.i);    }}class A implements Cloneable {    int i = 0;    A() {    }    A(int i) {        this.i = i;    }    public Object clone() throws CloneNotSupportedException {        return super.clone();    }}

运行时， 会出错， 错误信息如下：

C/C++ code

/*CloneTest.java:7: 不兼容的类型找到： java.lang.Object需要： A        a = b.clone();                   ^1 错误*/

为什么错了？ 怎么改？

[解决办法]
super.clone()返回的是父类的克隆对象（也就是Object对象），不是子类的克隆对象，所以强行转换就会失败

Java code

public Object clone() throws CloneNotSupportedException {    //return super.clone();    //如果是浅克隆    return this; //直接返回对象本身    //如果是深克隆    //return new A(this.i); //重新生成一个对象，并用当前对象的属性初始化新对象}
[解决办法]
Java code
public class CloneTest {    public static void main(String[] args) throws CloneNotSupportedException {        A a = new A();        A b = new A(3);        System.out.println(a.i);        System.out.println(b.i);        a = (A)b.clone();//要强转        System.out.println(a.i);        b.i = 5;        System.out.println(b.i);        System.out.println(a.i);    }}class A implements Cloneable {    int i = 0;    A() {    }    A(int i) {        this.i = i;    }        @Override    public Object clone() throws CloneNotSupportedException {        return super.clone();    }}
[解决办法]
克隆方法是先调用父类的clone方法，再将本类对象的属性赋给要克隆的对象
Java code
public class Test implements Cloneable{    int a = 0;    public static void main(String[] args) throws Exception    {    Test t = new Test();    t.a = 123;    Test t1 = (Test) t.clone();    System.out.println(t1 == t);    System.out.println(t1.a);    }    @Override    public Object clone()    {    try    {        Test t = (Test) super.clone();        t.a = this.a;        return t;    }    catch (CloneNotSupportedException e)    {        // this shouldn't happen, since we are Cloneable        throw new InternalError();    }    }}
[解决办法]
一个简单的编译错误,clone方法返回的是Object,你却把它赋值给A类的一个对象,所以需要强转一下:
Java code
try{a = (A)b.clone();}catch(CloneNotSupportedException e){  e.printStackTrace();}