夢與橋java之家

1、目的：為了獲得對象的一份拷貝。
2、一般步驟：§在派生類中覆蓋基類（object)的clone方法，并聲明為public
                          §在派生類的克隆方法中調用super.clone()
                          §在派生類中實現Cloneable接口

3、分類：淺拷貝、深拷貝
                    §淺拷貝僅僅拷貝所考慮的對象，而不拷貝它所引用的對象
                    §深拷貝把要拷貝的對象所引用的對象都拷貝了一遍
4、淺拷貝實例：

class Book implements Cloneable
{
 private String name;
 private double price;
 public Author author;

 Book(String name,double price,Author author)
 {
  this.name=name;
  this.price=price;
  this.author=author;
 }
 public String toString()
 {
  return "book's name:"+name+"\t\tbook's price:"+price+author.tostring();
 }
 public Object clone()
 {
  Object o=null;
  try
  {
   o=super.clone();
  }
  catch (CloneNotSupportedException e)
  {
   System.out.println(e.toString());
  }
  return o;
 }
}
class Author
{
 private String name;
 private int age;
 Author(String name,int age)
 {
  this.name=name;
  this.age=age;
 }
 public void set(String name,int age)
 {
  this.name=name;
  this.age=age;
 }
 public String tostring()
 {
  return "\nauthor's name:"+name+"\t\tauthor's age"+age;
 }
}
public class Test
{
 public static void main(String args[])
 {
  Author author=new Author("孫悟空",800);
  Book book1=new Book("高等數學",32.00,author);
  Book book2=(Book)book1.clone();
  book1.author.set("唐僧",700);//此處的修改影響到了book2，體現了淺拷貝的特點
  System.out.println(book2);
 }
}

5、深拷貝實例：

class Book implements Cloneable
{
 private String name;
 private double price;
 public Author author;

 Book(String name,double price,Author author)
 {
  this.name=name;
  this.price=price;
  this.author=author;
 }
 public String toString()
 {
  return "book's name:"+name+"\t\tbook's price:"+price+author.tostring();
 }
 public Object clone()
 {
  Book o=null;
  try
  {
   o=(Book)super.clone();
  }
  catch (CloneNotSupportedException e)
  {
   System.out.println(e.toString());
  }
  o.author=(Author)author.clone();
  return o;
 }
}
class Author implements Cloneable
{
 private String name;
 private int age;
 Author(String name,int age)
 {
  this.name=name;
  this.age=age;
 }
 public void set(String name,int age)
 {
  this.name=name;
  this.age=age;
 }
 public String tostring()
 {
  return "\nauthor's name:"+name+"\t\tauthor's age"+age;
 }
  public Object clone()
 {
  Object o=null;
  try
  {
   o=super.clone();
  }
  catch (CloneNotSupportedException e)
  {
   System.out.println(e.toString());
  }
  return o;
 }
}
public class Test
{
 public static void main(String args[])
 {
  Author author=new Author("孫悟空",800);
  Book book1=new Book("高等數學",32.00,author);
  Book book2=(Book)book1.clone();
  book1.author.set("唐僧",700);//此處的修改沒有影響book2，體現了深拷貝的特點。
  System.out.println(book2);
 }
}

6、注意：
            §在派生類中覆蓋Object的clone()方法時，一定要調用super.clone()，因為在運行時刻，Object中的clone()識別出你要復制的是哪一個對象，然后為此對象分配空間，并進行對象的復制，將原始對象的內容一一復制到新對象的存儲空間中。
            §在Object.clone()正式開始操作前，首先會檢查一個類是否Cloneable，即是否具有克隆能力——換言之，它是否實現了Cloneable接口。若未實現，Object.clone()就擲出一個CloneNotSupportedException違例，指出我們不能克隆它。