java多线程的学习心得

多线程没怎么用过，前几天经过同事提点。开始从多线程的功能上下手，于是呢，先写了一个线程循环交替打印的例子。

package com.thread;
/**
* 线程交替执行（通信：锁）
* 效果是1，2，A，3，4，B，5，6，C.......交替打印
* 线程a打印1，2
* 线程b打印A，B
*/
public class SignalCommunication {
public static final Object obj = new Object();
public static void main(String[] args) {
Thread a = new Thread(new Thread0());
Thread b = new Thread(new Thread1());
try {
a.start();
Thread.sleep(100);
b.start();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
class Thread0 implements Runnable {
private int num = 1;
@Override
public void run() {
while (num < 52) {
synchronized (SignalCommunication.obj) {
try {
SignalCommunication.obj.notify();
System.out.println(num);
num ++;
System.out.println(num);
num ++;
SignalCommunication.obj.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
}
class Thread1 implements Runnable {
private int ch = 65;
@Override
public void run() {
while (ch < 91) {
synchronized (SignalCommunication.obj) {
try {
SignalCommunication.obj.notify();
System.out.println((char)ch);
ch ++;
SignalCommunication.obj.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
}原理很简单，就是两个线程公用同一把锁SignalCommunication.obj，线程A得到锁之后，打印1，2，然后锁的状态是等待，线程A让出系统资源，线程B开始执行。同理，线程B执行完后，阻塞锁，让出资源。由此，同事得到一个问题，如果是多个线程交替执行呢。还能不能用这种方式。然后鼓捣了一天，写了出来
package com.thread;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
* 多个线程轮流打印，这里用到线程池
* @author GUCHUANG192
*
*/
public class MutiThread {
public static boolean flag = false;

public static void main(String[] args) {
int num = 5; //线程数量
doExecute(num);
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}

private static void doExecute(int num) {
ExecutorService pool = Executors.newFixedThreadPool(num);
Object[] oArray = new Object[num];
for (int i=0;i<num;i++) {
Object o = new Object();
oArray[i] = o;
}
for (int i = 0; i < oArray.length; i ++) {
try {
Thread6 t;
if (i == 0) {
t = new Thread6(oArray[oArray.length-1], oArray[i], (char)(i+65), num);
} else {
t = new Thread6(oArray[i-1], oArray[i], (char)(i+65), num);
}
Thread.sleep(100); //确保线程顺序执行
pool.execute(t);
if (i == oArray.length) {
flag = true;
}
} catch (Exception e) {
e.printStackTrace();
}
}
try {
Thread.sleep(2000);
pool.shutdownNow();
} catch (Exception e) {
e.printStackTrace();
}

}
}

class Thread6 extends Thread{
private char name; //打印字符
private Object prev; //当前线程执行前一个线程的锁
private Object curr; //当前线程的锁
private int count; //循环次数

public Thread6 (Object prev,Object curr,char name, int count) {
this.prev = prev;
this.curr = curr;
this.name = name;
this.count = count;
}

public void run () {
for (int i = 0; i < count; i ++) {
synchronized (prev) {
synchronized (curr) {
curr.notify();
System.out.println(Thread.currentThread().getName() + "：" + name);
}
try {
prev.wait();
} catch (Exception e) {
System.out.println(e.getMessage());
}
}
}
}
}

方法是参照网上看到的一个三个线程交替执行。由于忘了地址，没法引用。是酱紫的，每个线程拥有两把锁，一把锁是上一个线程的，一个是自己的。当前线程必须拥有上一个执行线程的锁，才可以往下执行。这样，第一个线程拥有最后一个线程的锁和自身的锁，完成闭合。循环执行，当然在执行前需要使用Thread.sleep(100);控制下执行顺序。