Java class implements "clone()" but throws CloneNotSupportedException-CodePudding

I've got code below, I expected that class My has overriden clone() function, it should work. But seems calling super.clone() throws out exception.

class My {
  @Override
  public My clone() {
    My ret = null;
    try {
      ret = (My)super.clone();
    } catch (CloneNotSupportedException e) {
      System.out.println("Should not reach here");
      e.printStackTrace();
    }
    return ret;
  }
}
public class UseClone implements Cloneable {
  public static void main(String[] args) {
    My nc = new My();
    My n2 = (My) nc.clone();
  }
}

It prints:

Should not reach here
java.lang.CloneNotSupportedException: mygroup.My
        at java.lang.Object.clone(Native Method)
        at mygroup.My.clone(UseClone.java:9)
        at mygroup.UseClone.main(UseClone.java:20)
        at org.codehaus.mojo.exec.ExecJavaMojo$1.run(ExecJavaMojo.java:254)
        at java.lang.Thread.run(Thread.java:748)

So how to make it work?

CodePudding user response：

You are cloning the My instance not the UseClone instance. Do class My implements Cloneable then it should be worked.

CodePudding user response：

You have defined a class "My" which has some issues. You have also defined UseClone, but it's only peripherally related so I'm leaving it out. Here is a stripped down class definition for My:

class My {
    @Override
    public My clone() {
        return super.clone();
    }
}

Trying to compile the My class from above results in the following error:

java: incompatible types: java.lang.Object cannot be converted to My

A few points about the code and the error:

You've called a method super.clone() where that method itself returns an object of type Object
That call (to super.clone()) does that because it resolves to Object.clone() which has this signature:
```
protected Object clone() throws CloneNotSupportedException
```
The compiler is telling you that the return type from super.clone() (again, return type Object) isn't compatible with the return type you have defined in your method signature:
```
public My clone() {
```

To fix your code:

Modify the My class to implement the Cloneable interface, changing from this:
```
class My {
```
to this:
```
class My implements Cloneable {
```

Change the return type in your method so that it returns Object instead of My:

class My implements Cloneable {
    public Object clone() {
        return super.clone();
    }
}

Add a throws clause to your clone() method, changing from this:

public Object clone() {

to this:

public Object clone() throws CloneNotSupportedException {

In the end, here's a basic working version of My class:

class My implements Cloneable {
    public Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
}

CodePudding user response：

The My calss should implement Cloneable

public class My implements Cloneable{
    public Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
}

public class UseClone implements Cloneable{
    public static void main(String[] args) throws CloneNotSupportedException {
        My nc = new My();
        My n2 = (My) nc.clone();
    }
}