java中深复制知识点详解

在正式开始深复制的讲解之前，我们先来理解一下概念。假设一个物品需要批量生产，但是这个物品还配有赠品，生产的时候需要把赠品也列在计划内。所谓深复制的原理就是这样，我们不能只复制属性，包括引用之类的附带也需要被复制。下面小编就为大家带来深复制的两种不同方法。

1.序列化实现

如下为谷歌gson序列化hashmap，实现深度复制的例子：

public class copydeepmaptest {
  public static void main(string[] args) {
    hashmap<integer, user> usermap = new hashmap<>();
    usermap.put(1, new user("jay", 26));
    usermap.put(2, new user("fany", 25));
    //shallow clone
    gson gson = new gson();
    string jsonstring = gson.tojson(usermap);
    type type = new typetoken<hashmap<integer, user>>(){}.gettype();
    hashmap<integer, user> clonedmap = gson.fromjson(jsonstring, type);
    //same as usermap
    system.out.println(clonedmap);
    system.out.println("\nchanges do not reflect in other map \n");
    //change a value is clonedmap
    clonedmap.get(1).setname("test");
    //verify content of both maps
    system.out.println(usermap);
    system.out.println(clonedmap);
  }
}

运行结果：

{1=user{name='jay', age=26}, 2=user{name='fany', age=25}}
changes do not reflect in other map 
{1=user{name='jay', age=26}, 2=user{name='fany', age=25}}
{1=user{name='test', age=26}, 2=user{name='fany', age=25}}

从运行结果看出，对clonemap修改，usermap没有被改变，所以是深度复制。

2.list深复制

两个list数据相同但是地址值不同，a和b是独立的两个list，a改变了b不会改变，b改变了a也不会改变

深复制的工具类方法:

public static <t> list<t> deepcopy(list<t> src) throws ioexception, classnotfoundexception {
bytearrayoutputstream byteout = new bytearrayoutputstream();
objectoutputstream out = new objectoutputstream(byteout);
out.writeobject(src);
bytearrayinputstream bytein = new bytearrayinputstream(byteout.tobytearray());
objectinputstream in = new objectinputstream(bytein);
@suppresswarnings("unchecked")
list<t> dest = (list<t>) in.readobject();
return dest;
}

关于深拷贝的一个扩展实例：

public class yuelylog implements serializable,cloneable {
  private attachment attachment;
  private string name;
  private string date;

  @override
  protected yuelylog clone() throws clonenotsupportedexception {
    return (yuelylog)super.clone();
  }

  public attachment getattachment() {
    return attachment;
  }

  public void setattachment(attachment attachment) {
    this.attachment = attachment;
  }

  public string getname() {
    return name;
  }

  public void setname(string name) {
    this.name = name;
  }

  public string getdate() {
    return date;
  }

  public void setdate(string date) {
    this.date = date;
  }

  /**
   * 使用序列化技术实现深拷贝
   * @return
   */
  public yuelylog deepclone() throws ioexception,classnotfoundexception{
    //将对象写入流中
    bytearrayoutputstream outputstream = new bytearrayoutputstream();
    objectoutputstream objectoutputstream = new objectoutputstream(outputstream);
    objectoutputstream.writeobject(this);
    //从流中取出
    bytearrayinputstream inputstream = new bytearrayinputstream(outputstream.tobytearray());
    objectinputstream objectinputstream = new objectinputstream(inputstream);
    return (yuelylog)objectinputstream.readobject();

  }
}