本文主要总结线程共享数据的相关知识,主要包括两方面:一是某个线程内如何共享数据,保证各个线程的数据不交叉;一是多个线程间如何共享数据,保证数据的一致性。
自己实现的话,是定义一个Map,线程为键,数据为值,表中的每一项即是为每个线程准备的数据,这样在一个线程中数据是一致的。
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 {//准备一个哈希表,为每个线程准备数据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);}}}上述代码偶尔会报异常:
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)
具体原因还不知道
API:
java.lang:Class ThreadLocal<T>
使用ThreadLocal类型的对象代替上面的Map即可
定义一个对象来封装多个变量,然后在ThreadLocal中存储整个对象
多变量时,最好将ThreadLocal类放在数据类的内部,数据类采用单例模式,这样,新建对象和获取对象都会更方便,同时封装性更强。
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);}}}/** * 将多变量封装起来的数据类 * 单例模式,内置ThreadLocal类型变量 */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;}}几种方式
最后一种方式的示例:
设计5个线程,其中三个线程每次对j增加1,另外两个线程对j每次减少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();}}}/** * 将共享数据封装在另一对象中(操作数据的方法也在该对象完成) */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;}}以上就是本文关于Java编程多线程之共享数据代码详解的全部内容,希望对大家有所帮助。感兴趣的朋友可以继续参阅本站其他相关专题,如有不足之处,欢迎留言指出。感谢朋友们对本站的支持!