基础知识
每个正在系统上运行的程序都是一个进程（process）。每个进程包含一到多个线程(thread)。进程也可能是整个程序或者是部分程序的动态执行。
线程是一组指令的集合，或者是程序的特殊段，它可以在程序里独立执行。也可以把它理解为代码运行的上下文。所以线程基本上是轻量级的进程，它负责在单个程序里执行多任务。
Java对多线程的支持是非常强大的，他屏蔽掉了许多的技术细节，让我们可以轻松的开发多线程的应用程序。Java里面有2个方法实现多线程，
1 继承 Thread类，比如
class MyThread extends Thread {
public void run() {
// 这里写上线程的内容
}
public static void main(String[] args) {
// 使用这个方法启动一个线程
new MyThread().start();
}
}
2 实现 Runnable接口，例如
class MyThread implements Runnable{
public void run() {
// 这里写上线程的内容
}
public static void main(String[] args) {
// 使用这个方法启动一个线程
new Thread(new MyThread()).start();
}
}
一般鼓励使用第二种方法，因为Java里面只允许单一继承，但允许实现多个接口。第二个方法更加灵活。
代码示例
多线程实现1－30的累计，其中共享资源池为1－30的数字的递增，采用了同步锁synchronized。
class Sum{ //共享资源，计数器count
private int count;//共享资源
public int add(){
synchronized(this){ //代码段1，共享锁，修饰程序段或者方法
count = count + 1;
System.out.println("add:" + count);
return count;
}
}
}
class SumThread implements Runnable{//定义线程
private Sum sd;
private int sum = 0;
private int [] a = new int[10]; public SumThread(String name, Sum sd){
super(name);
this.sd = sd;
}
public void run(){//必需的重写
try{
for(int i=0;i<10;i++){
a[i] = sd.add();
sum += a[i];
Thread.sleep(100);
}
Thread.sleep(1000);
}catch(Exception e){} System.out.println(getName() + "累加和:" + sum);
}
public void showData(){
System.out.print(getName() + "获得的数为");
for(int i=0;i<10;i++){
if(i%10==0)System.out.println();
System.out.print(a[i] + "+\t");
}
}
public int getSum(){
return sum;
}
}
public class SumDemo{
public static void main(String [] args){
Sum sd = new Sum();//代表共享资源的变量
SumThread s1 = new SumThread("线程1",sd);//创建完毕
SumThread s2 = new SumThread("线程2",sd);
SumThread s3 = new SumThread("线程3",sd);
Thread st1 = new Thread(s1);
Thread st2 = new Thread(s2);
Thread st3 = new Thread(s3);
st1.setPriority(Thread.MAX_PRIORITY); //代码段2
st2.setPriority(10);
st3.setPriority(1);
long begin = System.currentTimeMillis();
st1.start();//使线程运行
st2.start(); st3.start();
St1.join(); st2.join(); st3.join();
st1.showData();
st2.showData();
st3.showData();
System.out.println("总和为:" + (st1.getSum() + st2.getSum() + st3.getSum()));
long end = System.currentTimeMillis();
System.out.println(“探测localhost的TCP端口，共耗时” +
( end - begin)+"毫秒");
} }
TCP Socket多线程通信
服务端：
import java.io.*;
import java.net.*;
import java.util.*;
@SuppressWarnings(value={"deprecation","unchecked"}) //查阅该语句作用
public class MultiServer extends Thread{
ServerSocket serverSocket = null;
boolean listening = true;
int port = 1080;
int count;
public MultiServer(){
try{
serverSocket = new ServerSocket(port);
System.out.println("The Chat Server is listening on " + port);
}catch(IOException e){
System.err.println("Can't listen on Port");
System.exit(1);
}
count = 0;
while(listening){
try{
new ClientServiceThread(serverSocket.accept()).start();
count += 1;
System.out.println("The Chat Server get " + count + " Clients");
}catch(IOException e){
System.err.println("Can't Accept the Client Connection Apply");
}
}
try{
serverSocket.close();
}catch(IOException e){
System.exit(1);
}
this.start();
}
public static void main(String args[]){
MultiServer ms = new MultiServer();
} }
客户端：
class ClientServiceThread extends Thread{
private String name = "Client";
private Socket socket = null;
private Vector clients = null;
public ClientServiceThread(Socket socket){
super("ClientServiceThread");
this.socket = socket;
}
public ClientServiceThread(Vector clients, Socket socket){
super("ClientServiceThread");
this.socket = socket;
this.clients = clients;
}
public void run(){
try{
DataInputStream in = new DataInputStream(new
BufferedInputStream(socket.getInputStream()));
PrintStream out = new PrintStream(new
BufferedOutputStream(socket.getOutputStream(), 1024), true); String inputLine, outputLine; GreetingProtocol greeting = new GreetingProtocol();
outputLine = greeting.processInput(null); out.println("Welcome to My Chat Server, Please REG your Name, Format: name = yourname");
out.flush(); while((inputLine = in.readLine()) != null){
System.out.println(this.name + " Say: " + inputLine);
if(inputLine.startsWith("name")){
this.name =
inputLine.substring(inputLine.indexOf("=") + 1);
out.println("Your Name "+ this.name + " is REG");
out.flush();
}else{
outputLine = greeting.processInput(inputLine);
out.println(outputLine);
out.flush();
}
if(inputLine.equals("bye")) break;
}
out.close();
in.close();
socket.close();
}catch(IOException e){
e.printStackTrace();
} } }
