并发编程的艺术—

原文链接：https://blog.csdn.net/ftell/article/details/79353571#1 线程概念

文章目录

1 线程概念
2 创建任务和线程
3 Thread 类

1 线程概念

Java为创建和运行线程以及锁定资源以防止冲突提供了非常好的支持。你可以在程序中创建额外的线程以执行并发任务。在Java中，每个任务都是Runnable接口的实例，也称为一个runnable对象。一个线程实质上是一个对象，它为任务的执行提供便利。

public class TaskClass implements Runnable {public TaskClass(...) {}// 实现Runnable中的run方法public void run() {// 告诉系统如何运行自定义线程}
}public class Client {public void someMethod() {// 创建TaskClass的实例TaskClass task = new TaskClass(...);// 创建线程Thread thread = new Thread(task);// 启动线程thread.start();}
}

2 创建任务和线程

task类必须实现 Runnable接口，task必须从线程执行。
task是对象，为了创建task，必须首先为task定义一个实现了Runnable接口的类。Runnable接口相当简单，只包含了一个Run方法。

task必须在线程中执行，Thread类含有用于创建线程的构造函数，以及很多用于控制线程的方法，创建task的线程：

Thread thread = new Thread(task);

然后调用start()方法告诉JVM，线程已经可以运行：

thread.start();

JVM 通过调用task的run()方法执行task. 下面的例子，创建3个线程，分别打印’a’ 100 次，打印’b’ 100 次, 以及打印 0 ~ 100 之间的整数：

public class TaskThreadDemo {public static void main(String[] args) {// 创建taskRunnable printA = new PrintChar('a', 100);  // Runnable 改成 PrintChar 也可以Runnable printB = new PrintChar('b', 100);  // Runnable 改成 PrintChar 也可以Runnable print100 = new PrintNum(100);  // Runnable 改成 PrintNum 也可以// 创建线程Thread thread1 = new Thread(printA);Thread thread2 = new Thread(printB);Thread thread3 = new Thread(print100);// 启动线程thread1.start();thread2.start();thread3.start();}
}// 打印指定次数字符的 taskclass PrintChar implements Runnable {private char charToPrint; // The character to printprivate int times; // The number of times to repeat/** Construct a task with a specified character and number of* times to print the character*/public PrintChar(char c, int t) {charToPrint = c;times = t;}@Override /** Override the run() method to tell the system* what task to perform*/public void run() {for (int i = 0; i < times; i++) {System.out.print(charToPrint);}}
}// The task class for printing numbers from 1 to n for a given n
class PrintNum implements Runnable {private int lastNum;/** Construct a task for printing 1, 2, ..., n */public PrintNum(int n) {lastNum = n;}@Override /** Tell the thread how to run */public void run() {for (int i = 1; i <= lastNum; i++) {System.out.print(" " + i);}}
}

3 Thread 类

Thread 类包含了创建线程的构造函数以及控制线程的方法
Thread 类实现接口 Runnable:

                      << interface >>

java.lang.Thread -> java.lang.Runnable

因为Thread实现Runnable，因此可以定义类继承Thread并实现Run方法：

// 自定义thread类
public class CustomThread extends Thread {public CustomThread(...) {}// 重写Runnable里的run方法public void run() {// 告诉系统如何执行这个task}
}// 自定义类
public class Client {public void someMethod() {// 创建一个线程CustomThread thread1 = new CustomThread(...);// 启动线程thread1.start();// 创建另一个线程CustomThread thread2 = new CustomThread(...);// 启动线程thread2.start();}
}

例子：并行和串行

//package chapter01;/*** 并发和单线程执行测试* * @author tengfei.fangtf* @version $Id: ConcurrencyTest.java, v 0.1 2014-7-18 下午10:03:31 tengfei.fangtf Exp $*/
public class newtest {/** 执行次数 */private static final long count = 40000l;public static void main(String[] args) throws InterruptedException {//并发计算concurrency();//单线程计算serial();}private static void concurrency() throws InterruptedException {long start = System.currentTimeMillis();Thread thread = new Thread(new Runnable() {@Overridepublic void run() {int a = 0;for (long i = 0; i < count; i++) {a += 5;}System.out.println(a);}});thread.start(); //启动线程int b = 0;for (long i = 0; i < count; i++) {b--;}thread.join();long time = System.currentTimeMillis() - start;System.out.println("concurrency :" + time + "ms,b=" + b);}private static void serial() {long start = System.currentTimeMillis();int a = 0;for (long i = 0; i < count; i++) {a += 5;}int b = 0;for (long i = 0; i < count; i++) {b--;}long time = System.currentTimeMillis() - start;System.out.println("serial:" + time + "ms,b=" + b + ",a=" + a);}}