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Java編程多線程之共享數(shù)據(jù)代碼詳解

更新時(shí)間：2018年02月06日 11:52:37 作者：brianway

這篇文章主要介紹了Java編程多線程之共享數(shù)據(jù)代碼詳解，分享了相關(guān)代碼示例，小編覺得還是挺不錯(cuò)的，具有一定借鑒價(jià)值，需要的朋友可以參考下

本文主要總結(jié)線程共享數(shù)據(jù)的相關(guān)知識(shí)，主要包括兩方面:一是某個(gè)線程內(nèi)如何共享數(shù)據(jù)，保證各個(gè)線程的數(shù)據(jù)不交叉；一是多個(gè)線程間如何共享數(shù)據(jù)，保證數(shù)據(jù)的一致性。

線程范圍內(nèi)共享數(shù)據(jù)

自己實(shí)現(xiàn)的話，是定義一個(gè)Map,線程為鍵，數(shù)據(jù)為值,表中的每一項(xiàng)即是為每個(gè)線程準(zhǔn)備的數(shù)據(jù),這樣在一個(gè)線程中數(shù)據(jù)是一致的。

例子

package com.iot.thread;
import java.util.HashMap;
import java.util.Map;
import java.util.Random;
/**
 * Created by brian on 2016/2/4.
 */
public class ThreadScopeShareData {
	//準(zhǔn)備一個(gè)哈希表，為每個(gè)線程準(zhǔn)備數(shù)據(jù)
	private static Map<Thread,Integer> threadData = new HashMap<>();
	public static void main(String[] args) {
		for (int i=0;i<2;i++){
			new Thread(
			          new Runnable() {
				@Override
				        public void run() {
					int data = new Random().nextint();
					threadData.put(Thread.currentThread(),data);
					System.out.println(Thread.currentThread()+" put data："+data);
					new A().get();
					new B().get();
				}
			}
			).start();
		}
	}
	static class A{
		public void get(){
			int data = threadData.get(Thread.currentThread());
			System.out.println("A from "+Thread.currentThread()+" get data "+data);
		}
	}
	static class B{
		public void get(){
			int data = threadData.get(Thread.currentThread());
			System.out.println("B from "+Thread.currentThread()+" get data "+data);
		}
	}
}

上述代碼偶爾會(huì)報(bào)異常：

Exception in thread "Thread-0" java.lang.NullPointerException
at com.iot.thread.ThreadScopeShareData$A.get(ThreadScopeShareData.java:29)
at com.iot.thread.ThreadScopeShareData$1.run(ThreadScopeShareData.java:21)
at java.lang.Thread.run(Thread.java:745)

具體原因還不知道

ThreadLocal類

API:

java.lang:Class ThreadLocal<T>

單變量

使用ThreadLocal類型的對(duì)象代替上面的Map即可

多變量

定義一個(gè)對(duì)象來封裝多個(gè)變量，然后在ThreadLocal中存儲(chǔ)整個(gè)對(duì)象

多變量時(shí)，最好將ThreadLocal類放在數(shù)據(jù)類的內(nèi)部，數(shù)據(jù)類采用單例模式，這樣，新建對(duì)象和獲取對(duì)象都會(huì)更方便，同時(shí)封裝性更強(qiáng)。

示例代碼:

package com.iot.thread;
import java.util.Random;
/**
 * Created by brian on 2016/2/4.
 */
public class ThreadLocalTest {
	private static ThreadLocal<Integer> threadInger = new ThreadLocal<>();
	public static void main(String[] args) {
		for (int i=0;i<2;i++){
			new Thread(new Runnable() {
				@Override
				        public void run() {
					int data = new Random().nextint(100);
					threadInger.set(data);
					System.out.println(Thread.currentThread()+" put data："+data);
					MyThreadScopeData.getThreadInstance().setName(Thread.currentThread().toString());
					MyThreadScopeData.getThreadInstance().setAge(data%10);
					new A().get();
					new B().get();
				}
			}
			).start();
		}
	}
	static class A{
		public void get(){
			int data = threadInger.get();
			System.out.println("A from "+Thread.currentThread()+" get data "+data);
			MyThreadScopeData myThreadScopeData = MyThreadScopeData.getThreadInstance();
			System.out.println("A from "+myThreadScopeData);
		}
	}
	static class B{
		public void get(){
			int data = threadInger.get();
			System.out.println("B from "+Thread.currentThread()+" get data "+data);
			MyThreadScopeData myThreadScopeData = MyThreadScopeData.getThreadInstance();
			System.out.println("B from "+myThreadScopeData);
		}
	}
}
/**
 * 將多變量封裝起來的數(shù)據(jù)類
 * 單例模式，內(nèi)置ThreadLocal類型變量
 */
class MyThreadScopeData{
	private MyThreadScopeData(){
	}
	private static ThreadLocal<MyThreadScopeData> data = new ThreadLocal<>();
	public static MyThreadScopeData getThreadInstance(){
		MyThreadScopeData instance = data.get();
		if(instance == null){
			instance = new MyThreadScopeData();
			data.set(instance);
		}
		return instance;
	}
	private String name;
	private int age;
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	@Override
	  public String toString() {
		String reVal = super.toString()+"-{name,age}"+":{"+getName()+","+getAge()+"}";
		return reVal;
	}
}

多線程訪問共享數(shù)據(jù)

幾種方式

線程執(zhí)行代碼相同，使用同一Runnable對(duì)象，Runnable對(duì)象中有共享數(shù)據(jù)
線程執(zhí)行代碼不同，將共享數(shù)據(jù)封裝在另一對(duì)象中（操作數(shù)據(jù)的方法也在該對(duì)象完成），將這個(gè)對(duì)象逐一傳遞給各個(gè)Runnable對(duì)象。[本質(zhì)：共享數(shù)據(jù)的對(duì)象作為參數(shù)傳入Runnable對(duì)象]
線程執(zhí)行代碼不同，將Runnable對(duì)象作為某一個(gè)類的內(nèi)部類，共享數(shù)據(jù)作為這個(gè)外部類的成員變量（操作數(shù)據(jù)的方法放在外部類）。[本質(zhì):不同內(nèi)部類共享外部類數(shù)據(jù)]
結(jié)合上兩種方式，將共享數(shù)據(jù)封裝在另一對(duì)象中（操作數(shù)據(jù)的方法也在該對(duì)象完成），該對(duì)象作為這個(gè)外部類的成員變量，將Runnable對(duì)象作為內(nèi)部類

最后一種方式的示例:

設(shè)計(jì)5個(gè)線程，其中三個(gè)線程每次對(duì)j增加1，另外兩個(gè)線程對(duì)j每次減少1

package com.iot.thread;
/**
 * Created by brian on 2016/2/4.
 */
public class MutiThreadShareData {
	private static MutiShareData mutiShareData = new MutiShareData();
	public static void main(String[] args) {
		for (int i=0;i<3;i++){
			new Thread(
			          new Runnable() {
				@Override
				            public void run() {
					System.out.println(Thread.currentThread()+":{j from "+ mutiShareData.getJ()+" + to: "+mutiShareData.increment()+"}");
				}
			}
			).start();
		}
		for (int i=0;i<2;i++){
			new Thread(
			          new Runnable() {
				@Override
				            public void run() {
					System.out.println(Thread.currentThread()+":{j from "+ mutiShareData.getJ()+" - to: "+mutiShareData.decrement()+"}");
				}
			}
			).start();
		}
	}
}
/**
 * 將共享數(shù)據(jù)封裝在另一對(duì)象中（操作數(shù)據(jù)的方法也在該對(duì)象完成）
 */
class MutiShareData{
	private int j = 0;
	public synchronized int increment(){
		return ++j;
	}
	public synchronized int decrement(){
		return --j;
	}
	public synchronized int getJ() {
		return j;
	}
	public synchronized void setJ(int j) {
		this.j = j;
	}
}