Java - Prototype，制作深层拷贝

Question

我想问一下因为我是相当新的，这是制作文档对象的深层副本的正确方法，我不知道我是否正确地实现了字段的复制。

package model;

public class Document implements Cloneable {
    //fields
    private String author;
    private String date;
    private double versionID;
    private String contents;


    public Document(String author,String date,double versionID,String contents) {
         this.author=author;
         this.date=date;
         this.versionID=versionID;
         this.contents=contents;        
    }

    //getters-setters

    }
    //making the deep-copy clone all obj ref to Document
    @Override
    public Object clone() throws CloneNotSupportedException {
        Document doc =(Document)super.clone();
        doc.author=this.author;
        doc.date=this.date;
        doc.versionID=this.versionID;
        doc.contents=this.contents;

        return doc;
    }   

}