本文详细介绍了Java中多线程的实现方式，包括通过继承Thread类和实现Runnable接口创建线程的区别；探讨了线程的生命周期及如何通过join方法控制线程执行顺序；此外还深入讲解了线程同步机制，包括同步代码块、同步方法和Lock锁的使用方法。
1.main是主线程，使用继承Thread的方法，无法多线程之间共享实例属性，因为每new一个Thread有自己的属性i，所以不共享。
class FirstThread extends Thread
{
private int i;
//重写run方法
public void run(){
for(i=0; i<100; i++){
System.out.println(getName() + " " +i); //getName返回该线程的名字
}
}
public static void main(String[] args)
{
for(int i=0; i<100; i++){
System.out.println(Thread.currentThread().getName() + " " + i); //当前线程名字
if(i==20){
new FirstThread().start(); //创建启动第一条线程
new FirstThread().start(); //创建启动第二条线程
}
}
}
}
输出：
---------- 运行Java程序 ----------
main 0
main 1
main 2
main 3
main 4
main 5
main 6
main 7
main 8
main 9
main 10
main 11
main 12
main 13
main 14
main 15
main 16
main 17
main 18
main 19
main 20
Thread-0 0
Thread-0 1
main 21
Thread-0 2
main 22
Thread-0 3
Thread-0 4
Thread-1 0
Thread-1 1
Thread-1 2
Thread-1 3
........省略
2.继承Runnable接口的方法实现线程，由于创建线程时时同一个target的st，所以线程之间共享i，是连续的
class SecondThread implements Runnable
{
private int i;
public void run(){
for(; i<100; i++){
System.out.println(Thread.currentThread().getName() + " " + i);
}
}
public static void main(String[] args)
{
for(int i=0; i<100; i++){
System.out.println(Thread.currentThread().getName() + " " + i);
if(i==20){
SecondThread st = new SecondThread();
//(Runnable target, String name) SeconThread是同一个target，共享i
new Thread(st, "新线程1").start();
new Thread(st, "新线程2").start();
}
}
}
}
线程的生命周期
新建New
就绪Runnable start()以后处于就绪状态
运行running 执行run()方法时
阻塞Blocked 调用sleep等方法
死亡Dead run()方法执行完，异常，stop()等
控制线程 Join
main线程中调另一个线程jt.join()，main要等jt执行完毕才能执行
class JoinThread extends Thread
{
public JoinThread(String name){
super(name);
}
public void run(){
for(int i=0; i<100; i++){
System.out.println(getName() + " " + i);
}
}
public static void main(String[] args) throws Exception
{
new JoinThread("新线程").start();
for(int i=0; i<100; i++){
if(i==20){
JoinThread jt = new JoinThread("被Join线程");
jt.start();
//main线程调用jt的join方法，所以main线程要等jt执行完毕后才能执行
jt.join();
}
System.out.println(Thread.currentThread().getName() + " " + i);
}
}
}
后台线程
所有前台线程死亡后，后台线程就自动死亡，JVM的垃圾回收线程就是典型的后台线程
setDaemon必须在start之前设置
Thread t = new Thread();
t.setDaemon(true);
t.start();线程睡眠
暂停一段时间
public void run(){
for(int i=0; i<100; i++){
System.out.println(getName() + " " + i);
Thead.sleep(1000); //暂停1秒
}
}线程的让步
Thread.yield()优先级高的线程优先执行，高级执行完再执行低级，低级暂定
线程优先级设置
setPriority()
class ThreadYield extends Thread
{
private int i;
ThreadYield(String name){
super(name);
}
public void run(){
for(; i<100; i++){
System.out.println(getName() + " " + i);
if(i==0){
Thread.yield();
}
}
}
public static void main(String[] args)
{
ThreadYield ty1 = new ThreadYield("高级");
//ty1.setPriority(Thread.MAX_PRIORITY);
ty1.start();
ThreadYield ty2 = new ThreadYield("低级");
//ty2.setPriority(Thread.MIN_PRIORITY);
ty2.start();
}
}
线程的同步
不同时，num的值小于0了，还能继续计算，导致出错
class ThreadSafe implements Runnable
{
int num = 10;
public void run(){
for(int i=0; i<20; i++){
if(num>0){
try{
Thread.sleep(1000);
}catch(Exception e){
e.printStackTrace();
}
System.out.println("tickets:" + num--);
}
}
}
public static void main(String[] args)
{
ThreadSafe t = new ThreadSafe();
Thread A = new Thread(t);
Thread B = new Thread(t);
Thread C = new Thread(t);
Thread D = new Thread(t);
A.start();
B.start();
C.start();
D.start();
}
}
---------- 运行Java程序 ----------
tickets:10
tickets:10
tickets:8
tickets:9
tickets:7
tickets:5
tickets:6
tickets:7
tickets:4
tickets:3
tickets:4
tickets:2
tickets:1
tickets:0
tickets:1
tickets:-1
输出完成 (耗时 4 秒) - 正常终止
同步代码块
synchronized(Object){ } Object为任意代码块，标识位为0正在其他线程运行，1处于就绪状态
class ThreadSafe implements Runnable
{
int num = 10;
public void run(){
synchronized(""){
for(int i=0; i<20; i++){
if(num>0){
try{
Thread.sleep(1000);
}catch(Exception e){
e.printStackTrace();
}
System.out.println("tickets:" + num--);
}
}
}
}
public static void main(String[] args)
{
ThreadSafe t = new ThreadSafe();
Thread A = new Thread(t);
Thread B = new Thread(t);
Thread C = new Thread(t);
Thread D = new Thread(t);
A.start();
B.start();
C.start();
D.start();
}
}
---------- 运行Java程序 ----------
tickets:10
tickets:9
tickets:8
tickets:7
tickets:6
tickets:5
tickets:4
tickets:3
tickets:2
tickets:1
输出完成 (耗时 10 秒) - 正常终止
同步方法
run方法不能设置为同步方法
class ThreadSafe implements Runnable
{
int num = 10;
public void run(){
doit();
}
public synchronized void doit(){
for(int i=0; i<20; i++){
if(num>0){
try{
Thread.sleep(1000);
}catch(Exception e){
e.printStackTrace();
}
System.out.println("tickets:" + num--);
}
}
}
public static void main(String[] args)
{
ThreadSafe t = new ThreadSafe();
Thread A = new Thread(t);
Thread B = new Thread(t);
Thread C = new Thread(t);
Thread D = new Thread(t);
A.start();
B.start();
C.start();
D.start();
}
}
---------- 运行Java程序 ----------
tickets:10
tickets:9
tickets:8
tickets:7
tickets:6
tickets:5
tickets:4
tickets:3
tickets:2
tickets:1
输出完成 (耗时 10 秒) - 正常终止
同步锁 Lock
ReentrantLock类，lock()和unlock()方法
import java.util.concurrent.locks.ReentrantLock;
class ThreadSafe implements Runnable
{
private final ReentrantLock lock = new ReentrantLock();
int num = 10;
public void run(){
lock.lock();
try{
for(int i=0; i<20; i++){
if(num>0){
try{
Thread.sleep(1000);
}catch(Exception e){
e.printStackTrace();
}
System.out.println("tickets:" + num--);
}
}
}finally{
lock.unlock();
}
}
public static void main(String[] args)
{
ThreadSafe t = new ThreadSafe();
Thread A = new Thread(t);
Thread B = new Thread(t);
Thread C = new Thread(t);
Thread D = new Thread(t);
A.start();
B.start();
C.start();
D.start();
}
}
---------- 运行Java程序 ----------
tickets:10
tickets:9
tickets:8
tickets:7
tickets:6
tickets:5
tickets:4
tickets:3
tickets:2
tickets:1
输出完成 (耗时 10 秒) - 正常终止
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