Question

我想知道是否有办法做到以下几点。我有一个抽象类，Shape，以及它的所有不同的子类，我想覆盖克隆方法。我想在方法中做的就是从当前的Shape创建一个新的toString()。显然我无法做到以下因为Shape是抽象的。还有另一种方法可以做到这一点，因为在每个子类中重写克隆只是为了简单的名称更改似乎没用。

public abstract class Shape {

    public Shape(String str) {
        // Create object from string representation
    }

    public Shape clone() {
        // Need new way to do this
        return new Shape(this.toString());   
    }

    public String toString() {
        // Correctly overriden toString()
    }
}

Answer 1

您可以尝试使用反射：

public abstract class AClonable implements Cloneable{

private String val;

public AClonable(){

}

public AClonable(String s){
    val=s;
}

public String toString(){
    return val;
}

@Override
public AClonable clone(){
    try {
        System.out.println(getClass().getCanonicalName());
        AClonable b= getClass().getDeclaredConstructor(String.class).newInstance(val);

        return b;
    } catch (InstantiationException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IllegalAccessException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IllegalArgumentException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (SecurityException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (InvocationTargetException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (NoSuchMethodException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    return null;
}

}

在clone（）方法中调用getClass（）。因为ACloneble是抽象的，所以总是会调用具体的类。

   public class ClonebaleOne extends AClonable{

public ClonebaleOne(){
    super();
}

public ClonebaleOne(String s) {
    super(s);
    // TODO Auto-generated constructor stub
}

}

和

  public class ClonebaleTwo extends AClonable{

public ClonebaleTwo(){
    super();
}

public ClonebaleTwo(String s) {
    super(s);
    // TODO Auto-generated constructor stub
}

}

最后

   public static void main(String[] args){
    AClonable one = new ClonebaleOne("One");
    AClonable tow= new ClonebaleTwo("Two");
    AClonable clone = one.clone();
    System.out.println(clone.toString());
    clone = tow.clone();
    System.out.println(clone.toString());

}

输出：

  ClonebaleOne
  One
  ClonebaleTwo
  Two

但它更像是一个黑客而非解决方案

[编辑]我的两个克隆比...更快

[编辑]完成。 clone（）的另一个实现可以是

 @Override
public AClonable clone(){
    try {
        ByteArrayOutputStream outByte = new ByteArrayOutputStream();
        ObjectOutputStream outObj = new ObjectOutputStream(outByte);
        ByteArrayInputStream inByte;
        ObjectInputStream inObject;
        outObj.writeObject(this);
        outObj.close();
        byte[] buffer = outByte.toByteArray();
        inByte = new ByteArrayInputStream(buffer);
        inObject = new ObjectInputStream(inByte);
        @SuppressWarnings("unchecked")
        Object deepcopy =  inObject.readObject();
        inObject.close();
        return (AClonable) deepcopy;
    } catch (Exception e) {
        e.printStackTrace();
    }
    return null;
}

当您的抽象类实现Serialazable时。在那里，您将对象写入光盘并使用光盘中的值创建副本。

Answer 2

您无法创建abstract类的深层克隆，因为无法实例化。您只需使用Object.clone()或返回this

即可浅层克隆

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

或

@Override
public Object clone() throws CloneNotSupportedException {
    return this;
}

抽象类可以作为引用，它不能有一个实例，所以在这种情况下浅克隆工作

OR

作为一种更好的方法，您可以将clone()声明为abstract并让子类定义它，就像这样

abstract class Shape {

    private String str;

    public Shape(String str) {
        this.str = str;
    }

    public abstract Shape clone();

    public String toString() {
        return str;
    }
}

class Circle extends Shape {

    public Circle(String str) {
        super(str);
    }

    @Override
    public Shape clone() {
        return new Circle("circle");
    }

}

Answer 3

虽然我怀疑这是个好主意，但你可以使用反思：

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;

public class Test {

    public static void main(String[] args) {        
        Square s1 = new Square("test");
        Square s2 = (Square) s1.clone();

        // show that s2 contains the same data  
        System.out.println(s2);
        // show that s1 and s2 are really different objects
        System.out.println(s1 == s2);
    }

    public static abstract class Shape {
        private String str;

        public Shape(String str) {
            this.str = str;
        }

        public Shape clone() {          
            try {
                Class<?> cl = this.getClass();
                Constructor<?> cons = cl.getConstructor(String.class);
                return (Shape) cons.newInstance(this.toString());           
            } catch (NoSuchMethodException | SecurityException |
                     InstantiationException | IllegalAccessException |
                     IllegalArgumentException | InvocationTargetException e) {  
                e.printStackTrace();
            }           

            return null;
        }

        @Override
        public String toString() {
            return str;
        }
    }

    public static class Square extends Shape {
        public Square(String str) {
            super(str);
        }
    }   
}

Answer 4

您可以通过反思来解决：

public abstract class Shape {

    private String str;

    public Shape()  {

    }

    protected Shape(String str) {
        this.str = str;
    }

    public Shape clone() throws CloneNotSupportedException
    {
        try {
            return (Shape)getClass().getDeclaredConstructor(String.class).newInstance(this.toString());
        } catch (Exception e) {
            throw new CloneNotSupportedException();
        }
    }

    public String toString() {
        return "shape";
    }

public class Round extends Shape
{
    public Round()
    {
        super();
    }
    protected Round(String str) {
        super(str);
    }

    @Override
    public String toString() {
        return "round";
    }
}

main(){
  Shape round = new Round();        
  Shape clone = round.clone();
  System.out.println(round);
  System.out.println(clone);
}

但是 - IMO - 实施效果差，容易出错并且有很多坑; Cloneable和Object.clone()的最佳用法是不使用它们！你有很多方法可以做同样的事情（如深度克隆的序列化）和浅克隆，可以更好地控制流量。

Java克隆抽象对象

4 个答案: