Java数据结构源码分析-前言

缺乏、安全感 2022-08-23 00:51 175阅读 0赞

## 1.Cloneable和Serializable ##

从声明中有两点是需要说明的，其也存在与其他的集合结构中Cloneable和Serializable

public class HashSet<E> extends AbstractSet<E> implements Set<E>, Cloneable, java.io.Serializable { }

### 1.1 Cloneabale ###

从下面片段可以看到Cloneable接口并没有任何的方法，其是一个标志性接口，只有实现该接口的类才能调用clone()方法来复制堆上的对象而不是引用.

public interface Cloneable { }
    
    public class CloneBean implements Cloneable { 
        private String name;
    
        public CloneBean(String name){
            this.name=name;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        @Override
        protected Object clone() throws CloneNotSupportedException {
            return super.clone();
        }
    
        public static void main(String[] args) throws CloneNotSupportedException {
            CloneBean fromCloneBean=new CloneBean("OldCloneBean");
            CloneBean toCloneBean=(CloneBean)fromCloneBean.clone();
            toCloneBean.setName("newCloneBean");
            System.out.println(fromCloneBean.name + " vs " + toCloneBean.name);
    
            CloneBean sameCloneBean=fromCloneBean;
            sameCloneBean.setName("SameCloneBean");
            System.out.println(fromCloneBean.name + " vs " + sameCloneBean.name);
        }
    }
    
    //输入结果：
    //OldCloneBean vs newCloneBean
    //SameCloneBean vs SameCloneBean
    
    package com.job.search.blog.code;
    
    /** * Created by wenyi on 16/6/3. * Email:caowenyi@meituan.com */
    public class CloneBean { 
        private String name;
    
        public CloneBean(String name){
            this.name=name;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        @Override
        protected Object clone() throws CloneNotSupportedException {
            return super.clone();
        }
    
        public static void main(String[] args) throws CloneNotSupportedException {
            CloneBean fromCloneBean=new CloneBean("OldCloneBean");
            CloneBean toCloneBean=(CloneBean)fromCloneBean.clone();
            toCloneBean.setName("newCloneBean");
            System.out.println(fromCloneBean.name + " vs " + toCloneBean.name);
        }
    }
    //输入结果：Exception in thread "main" java.lang.CloneNotSupportedException: com.job.search.blog.code.CloneBean

Java中对象保存于堆上，而引用保存于栈中，因此CloneBean sameCloneBean=fromCloneBean是两个不同名字的引用作用于同一个对象上，因此任意一个引用更改对象都要影响另外一个。为了真正的产生两个对象就需要使用继承于Object的clone()方法。从实验二可以看出如果不在类上生命其是Cloneable的，在调用clone（）方法时会产生异常。  
另外上面的只是一种浅拷贝，其并不会拷贝对象的field中的对象，而是引用间的赋值。从下面的实验一可以看出CloneBean中的UserBean还是在copy引用，对任意CloneBean中的UserBean的操作都会影响两个CloneBean.  
深层次的拷贝，除了要拷贝对象本身还要拷贝对象域中的每个一个对象

public class CloneBean implements Cloneable { 
        private String name;
        private UserBean userBean;
    
        public CloneBean(String name, UserBean userBean) {
            this.name = name;
            this.userBean = userBean;
        }
    
        @Override
        protected Object clone() throws CloneNotSupportedException {
            return super.clone();
        }
    
        public static void main(String[] args) throws CloneNotSupportedException {
            String name = "CloneBeanName";
            UserBean userBean = new UserBean("OldUserBean");
            CloneBean fromCloneBean = new CloneBean(name, userBean);
            CloneBean toCloneBean = (CloneBean) fromCloneBean.clone();
            toCloneBean.name="NewBeanName";
            userBean.setName("NewUserBean");
            System.out.println(fromCloneBean.name + "_" + fromCloneBean.userBean + " vs " + toCloneBean.name + "_" + toCloneBean.userBean);
        }
    }
    
    //输入结果：CloneBeanName_NewUserBean vs NewBeanName_NewUserBean
    
    package com.job.search.blog.code;
    
    /** * Created by wenyi on 16/6/3. * Email:caowenyi@meituan.com */
    public class CloneBean implements Cloneable { 
        private String name;
        private UserBean userBean;
    
        public CloneBean(String name, UserBean userBean) {
            this.name = name;
            this.userBean = userBean;
        }
    
        @Override
        protected Object clone() throws CloneNotSupportedException {
            CloneBean cloneBean = (CloneBean) super.clone();
            cloneBean.userBean = (UserBean) this.userBean.clone();
            return cloneBean;
        }
    
        public static void main(String[] args) throws CloneNotSupportedException {
            String name = "CloneBeanName";
            UserBean userBean = new UserBean("OldUserBean");
            CloneBean fromCloneBean = new CloneBean(name, userBean);
            CloneBean toCloneBean = (CloneBean) fromCloneBean.clone();
            toCloneBean.name = "NewBeanName";
            userBean.setName("NewUserBean");
            System.out.println(fromCloneBean.name + "_" + fromCloneBean.userBean + " vs " + toCloneBean.name + "_" + toCloneBean.userBean);
        }
    }
    //输出结果：CloneBeanName_NewUserBean vs NewBeanName_OldUserBean

### 1.2 Serializable ###

对于深层拷贝除了上述所使用的方法，其也可以通过Serializable来间接实现。Seriablizable同Cloneable一样其表示该类的对象是可以被序列化到文件或者在网络流中传播，并被反序列化。  
序列化代码如下：

public static <T> void writeObjectToFileName(T src, String filename) throws RuntimeException {
            ObjectOutputStream out = null;
            try {
                out = new ObjectOutputStream(new FileOutputStream(new File(filename)));
                out.writeObject(src);
                out.flush();
            } catch (Exception e) {
                throw new RuntimeException(e);
            } finally {
                if (out != null)
                    try {
                        out.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
            }
        }
    
        public static <T> T readObjectFromFileName(String filename) throws RuntimeException {
            ObjectInputStream in = null;
            T dist;
            try {
                in = new ObjectInputStream(new FileInputStream(new File(filename)));
                dist = (T) in.readObject();
            } catch (Exception e) {
                throw new RuntimeException(e);
            } finally {
                if (in != null)
                    try {
                        in.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
            }
            return dist;
        }

该段代码实现的功能是将一个对象二进制编码到文件中，并同时提供了新建一个对象，并读取该对象在二进制文件中存取的数据。因此其序列化前后是两个不同的对象。注意：同Cloneable一样，任何可以序列化的对象除本身可以序列化（实现Seriable接口）,其域Field也要实现Seriable接口。  
如下是一个通过Seriable实现对象深层拷贝的方法：

package com.job.search.blog.code;
    
    import java.io.*;
    
    @SuppressWarnings("unchecked")
    public abstract class BeanUtil {
    
        public static <T> T cloneTo(T src) throws RuntimeException {
            ByteArrayOutputStream memoryBuffer = new ByteArrayOutputStream();
            ObjectOutputStream out = null;
            ObjectInputStream in = null;
            T dist = null;
            try {
                out = new ObjectOutputStream(memoryBuffer);
                out.writeObject(src);
                out.flush();
                in = new ObjectInputStream(new ByteArrayInputStream(memoryBuffer.toByteArray()));
                dist = (T) in.readObject();
            } catch (Exception e) {
                throw new RuntimeException(e);
            } finally {
                if (out != null)
                    try {
                        out.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                if (in != null)
                    try {
                        in.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
            }
            return dist;
        }
    
        public static <T> void writeObjectToFileName(T src, String filename) throws RuntimeException {
            ObjectOutputStream out = null;
            try {
                out = new ObjectOutputStream(new FileOutputStream(new File(filename)));
                out.writeObject(src);
                out.flush();
            } catch (Exception e) {
                throw new RuntimeException(e);
            } finally {
                if (out != null)
                    try {
                        out.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
            }
        }
    
        public static <T> T readObjectFromFileName(String filename) throws RuntimeException {
            ObjectInputStream in = null;
            T dist;
            try {
                in = new ObjectInputStream(new FileInputStream(new File(filename)));
                dist = (T) in.readObject();
            } catch (Exception e) {
                throw new RuntimeException(e);
            } finally {
                if (in != null)
                    try {
                        in.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
            }
            return dist;
        }
    
        public static void main(String[] args) {
            CloneBean fromCloneBean = new CloneBean("OldName", new UserBean("OldUser"));
            CloneBean toCloneBean = BeanUtil.cloneTo(fromCloneBean);
            toCloneBean.setName("NewName");
    
            System.out.println("Old="+fromCloneBean+" New="+toCloneBean);
        }
    }
    //输入出结果如下：Old=com.job.search.blog.code.CloneBean@715a64e6 New=com.job.search.blog.code.CloneBean@2b237512
    //OldName vs NewName

从结果中可以看出对象已将被深层次的拷贝了