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Java中的深拷貝(深復(fù)制)和淺拷貝(淺復(fù)制)介紹

更新時(shí)間：2015年03月26日 20:56:56 作者：Microgoogle

這篇文章主要介紹了Java中的深拷貝(深復(fù)制)和淺拷貝(淺復(fù)制)介紹,需要的朋友可以參考下

深拷貝(深復(fù)制)和淺拷貝(淺復(fù)制)是兩個(gè)比較通用的概念，尤其在C++語言中，若不弄懂，則會(huì)在delete的時(shí)候出問題，但是我們?cè)谶@幸好用的是Java。雖然java自動(dòng)管理對(duì)象的回收，但對(duì)于深拷貝(深復(fù)制)和淺拷貝(淺復(fù)制)，我們還是要給予足夠的重視，因?yàn)橛袝r(shí)這兩個(gè)概念往往會(huì)給我們帶來不小的困惑。

淺拷貝是指拷貝對(duì)象時(shí)僅僅拷貝對(duì)象本身（包括對(duì)象中的基本變量），而不拷貝對(duì)象包含的引用指向的對(duì)象。深拷貝不僅拷貝對(duì)象本身，而且拷貝對(duì)象包含的引用指向的所有對(duì)象。舉例來說更加清楚：對(duì)象A1中包含對(duì)B1的引用，B1中包含對(duì)C1的引用。淺拷貝A1得到A2，A2 中依然包含對(duì)B1的引用，B1中依然包含對(duì)C1的引用。深拷貝則是對(duì)淺拷貝的遞歸，深拷貝A1得到A2，A2中包含對(duì)B2（B1的copy）的引用，B2 中包含對(duì)C2（C1的copy）的引用。

若不對(duì)clone()方法進(jìn)行改寫，則調(diào)用此方法得到的對(duì)象即為淺拷貝，下面我們著重談一下深拷貝。

運(yùn)行下面的程序，看一看淺拷貝：

class Professor0 implements Cloneable { 
  String name; 
  int age; 
 
  Professor0(String name, int age) { 
    this.name = name; 
    this.age = age; 
  } 
 
  public Object clone() throws CloneNotSupportedException { 
    return super.clone(); 
  } 
} 
 
class Student0 implements Cloneable { 
  String name;// 常量對(duì)象。 
  int age; 
  Professor0 p;// 學(xué)生1和學(xué)生2的引用值都是一樣的。 
 
  Student0(String name, int age, Professor0 p) { 
    this.name = name; 
    this.age = age; 
    this.p = p; 
  } 
 
  public Object clone() { 
    Student0 o = null; 
    try { 
      o = (Student0) super.clone(); 
    } catch (CloneNotSupportedException e) { 
      System.out.println(e.toString()); 
    } 
 
    return o; 
  } 
} 
 
public class ShallowCopy { 
  public static void main(String[] args) { 
    Professor0 p = new Professor0("wangwu", 50); 
    Student0 s1 = new Student0("zhangsan", 18, p); 
    Student0 s2 = (Student0) s1.clone(); 
    s2.p.name = "lisi"; 
    s2.p.age = 30; 
    s2.name = "z"; 
    s2.age = 45; 
    System.out.println("學(xué)生s1的姓名：" + s1.name + "\n學(xué)生s1教授的姓名：" + s1.p.name + "," + "\n學(xué)生s1教授的年紀(jì)" + s1.p.age);// 學(xué)生1的教授 
  } 
}

s2變了，但s1也變了，證明s1的p和s2的p指向的是同一個(gè)對(duì)象。這在我們有的實(shí)際需求中，卻不是這樣，因而我們需要深拷貝：

class Professor implements Cloneable { 
  String name; 
  int age; 
 
  Professor(String name, int age) { 
    this.name = name; 
    this.age = age; 
  } 
 
  public Object clone() { 
    Object o = null; 
    try { 
      o = super.clone(); 
    } catch (CloneNotSupportedException e) { 
      System.out.println(e.toString()); 
    } 
    return o; 
  } 
} 
 
class Student implements Cloneable { 
  String name; 
  int age; 
  Professor p; 
 
  Student(String name, int age, Professor p) { 
    this.name = name; 
    this.age = age; 
    this.p = p; 
  } 
 
  public Object clone() { 
    Student o = null; 
    try { 
      o = (Student) super.clone(); 
    } catch (CloneNotSupportedException e) { 
      System.out.println(e.toString()); 
    } 
    o.p = (Professor) p.clone(); 
    return o; 
  } 
} 
 
public class DeepCopy { 
  public static void main(String args[]) { 
    long t1 = System.currentTimeMillis(); 
    Professor p = new Professor("wangwu", 50); 
    Student s1 = new Student("zhangsan", 18, p); 
    Student s2 = (Student) s1.clone(); 
    s2.p.name = "lisi"; 
    s2.p.age = 30; 
    System.out.println("name=" + s1.p.name + "," + "age=" + s1.p.age);// 學(xué)生1的教授不改變。 
    long t2 = System.currentTimeMillis(); 
    System.out.println(t2-t1); 
  } 
}

當(dāng)然我們還有一種深拷貝方法，就是將對(duì)象串行化：

import java.io.*; 
//Serialization is time-consuming 
class Professor2 implements Serializable { 
  /** 
   * 
   */
  private static final long serialVersionUID = 1L; 
  String name; 
  int age; 
 
  Professor2(String name, int age) { 
    this.name = name; 
    this.age = age; 
  } 
} 
 
class Student2 implements Serializable { 
  /** 
   * 
   */
  private static final long serialVersionUID = 1L; 
  String name;// 常量對(duì)象。 
  int age; 
  Professor2 p;// 學(xué)生1和學(xué)生2的引用值都是一樣的。 
 
  Student2(String name, int age, Professor2 p) { 
    this.name = name; 
    this.age = age; 
    this.p = p; 
  } 
 
  public Object deepClone() throws IOException, OptionalDataException, 
      ClassNotFoundException { 
    // 將對(duì)象寫到流里 
    ByteArrayOutputStream bo = new ByteArrayOutputStream(); 
    ObjectOutputStream oo = new ObjectOutputStream(bo); 
    oo.writeObject(this); 
    // 從流里讀出來 
    ByteArrayInputStream bi = new ByteArrayInputStream(bo.toByteArray()); 
    ObjectInputStream oi = new ObjectInputStream(bi); 
    return (oi.readObject()); 
  } 
 
} 
 
public class DeepCopy2 { 
 
  /** 
   * @param args 
   */
  public static void main(String[] args) throws OptionalDataException, 
      IOException, ClassNotFoundException { 
    long t1 = System.currentTimeMillis(); 
    Professor2 p = new Professor2("wangwu", 50); 
    Student2 s1 = new Student2("zhangsan", 18, p); 
    Student2 s2 = (Student2) s1.deepClone(); 
    s2.p.name = "lisi"; 
    s2.p.age = 30; 
    System.out.println("name=" + s1.p.name + "," + "age=" + s1.p.age); // 學(xué)生1的教授不改變。 
    long t2 = System.currentTimeMillis(); 
    System.out.println(t2-t1); 
  } 
 
}

但是串行化卻很耗時(shí)，在一些框架中，我們便可以感受到，它們往往將對(duì)象進(jìn)行串行化后進(jìn)行傳遞，耗時(shí)較多。

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