JAVA基础--线程
sleep和wait的区别:
1. sleep是Thread的方法, wait是object的方法
2. sleep占着CPU睡觉, wait等待CPU,不占用CPU
线程是一个程序内部的顺序控制流
线程和进程的区别:
1. 每个进程都有独立的代码和数据空间, 进程间的切换会有很大的开销.
2. 线程可以看成是轻量级的进程, 同一类线程共享代码和数据空间, 每个线程有独立的运行栈和程序计数器PC, 线程切换的开销小.
3. 多进行, 在操作系统中能同时运行多个任务(程序)
4. 多线程:在同一个程序可以有多个顺序刘同时执行.
通过创建Thread的实例来创建新的线程
每个线程都通过特定Thread对象对应的run方法来完成操作, 方法run称为线程体
通过调用Thread类的start方法启动一个线程
run是方法调用,start是开启一个线程
以下程序只有一个线程 main, 主线程
public class {
public static void main(String[] args) {
m1();
}
public static void m1() {
m2();
m3();
}
public static void m2() {}
public static void m3() {}
}
进程: 一个class文件, 一个exe文件, 是个静态的概念.进程的执行指的是一个主线程开始执行, 即main开始.
所以机器里我们运行的都是线程.
建议使用以下接口的方式:
public class TestThread1 {
public static void main(String args[]) {
Runner1 r = new Runner1();
Thread t = new Thread(r);
t.start();
for(int i=0; i<100; i++) {
System.out.println("Main Thread:------" + i);
}
}
}
class Runner1 implements Runnable {
public void run() {
for(int i=0; i<100; i++) {
System.out.println("Runner1 :" + i);
}
}
}
还有一种方法,继承Thread,不建议使用:
public class TestThread1 {
public static void main(String args[]) {
Runner1 r = new Runner1();
r.start();
for(int i=0; i<100; i++) {
System.out.println("Main Thread:------" + i);
}
}
}
class Runner1 extends Thread {
public void run() {
for(int i=0; i<100; i++) {
System.out.println("Runner1 :" + i);
}
}
}
线程状态转换:
创建-->start-->就绪--> 运行-->终止 运行-->阻塞状态-->就绪
线程控制的方法:
isAlive(): 阻塞,运行, 就绪,
getPriority() 获得优先级
setPriority(): 设置优先级
Thread.sleep(): 将当前线程睡眠指定毫秒数
join(): 合并, 等改线程结束再恢复当前线程的运行
yield(): 让出CPU, 当前线程进去就绪状态等待调度
wait(): 当前线程进入wait pool
sleep方法: Thread类的静态方法:
import java.util.*;
public class TestInterrupt {
public static void main(String[] args) {
Runner r = new Runner();
Thread t = new Thread(r);
t.start();
try {Thread.sleep(10000);}
catch (InterruptedException e) {}
//t.interrupt(); //打断子线程,比较粗暴
r.flag=false; //替换上面的打断子线程的方式, 用这种方式, run方法里的return也可以注释掉了
}
}
class Runner implements Runnable {
boolean flag = true;
public void run(){
while(flag){
System.out.println("==="+new Date()+"===");
try {
Thread.sleep(1000);
} catch (InterruptedException e) { //被打算后进入异常, return
return;
}
}
}
}
结果:每隔一秒显示一次:
===Fri Apr 08 10:53:44 CST 2016=== ===Fri Apr 08 10:53:45 CST 2016=== ===Fri Apr 08 10:53:46 CST 2016=== ===Fri Apr 08 10:53:47 CST 2016=== ===Fri Apr 08 10:53:48 CST 2016=== ===Fri Apr 08 10:53:49 CST 2016=== ===Fri Apr 08 10:53:50 CST 2016=== ===Fri Apr 08 10:53:51 CST 2016=== ===Fri Apr 08 10:53:52 CST 2016=== ===Fri Apr 08 10:53:53 CST 2016===
join用法:相当于调用, 如果main里调用join, 那么会等join的线程执行完才能执行自己的线程:
public class TestJoin {
public static void main(String[] args) {
MyThread2 t1 = new MyThread2("abcde");
t1.start();
try {
t1.join();
} catch (InterruptedException e) {}
for(int i=1;i<=10;i++){
System.out.println("i am main thread");
}
}
}
class MyThread2 extends Thread {
MyThread2(String s){
super(s);
}
public void run(){
for(int i =1;i<=10;i++){
System.out.println("i am "+getName());
try {
sleep(1000);
} catch (InterruptedException e) {
return;
}
}
}
}
结果:
i am abcde i am abcde i am abcde i am abcde i am abcde i am abcde i am abcde i am abcde i am abcde i am abcde i am main thread i am main thread i am main thread i am main thread i am main thread i am main thread i am main thread i am main thread i am main thread i am main thread
yield方法: 让出CPU, 给其他线程执行的机会:
只要运行的线程 i 被10整除, 就让出给别的线程运行
public class TestYield {
public static void main(String[] args) {
MyThread3 t1 = new MyThread3("t1");
MyThread3 t2 = new MyThread3("t2");
t1.start(); t2.start();
}
}
class MyThread3 extends Thread {
MyThread3(String s){super(s);}
public void run(){
for(int i =1;i<=100;i++){
System.out.println(getName()+": "+i);
if(i%10==0){
yield();
}
}
}
}
线程的优先级:
public class TestPriority {
public static void main(String[] args) {
Thread t1 = new Thread(new T1());
Thread t2 = new Thread(new T2());
t1.setPriority(Thread.NORM_PRIORITY + 3);
t1.start();
t2.start();
}
}
class T1 implements Runnable {
public void run() {
for(int i=0; i<100; i++) {
System.out.println("T1: " + i);
}
}
}
class T2 implements Runnable {
public void run() {
for(int i=0; i<100; i++) {
System.out.println("------T2: " + i);
}
}
}
Thread.MIN_PRIORITY=1; Thread.MAX_PRIORITY=10; Thread.NORM_PRIORITY=5;
同一个线程对象可以定义两个Thread:
public class TestThread2 {
public static void main(String args[]) {
Runner2 r = new Runner2();
Thread t1 = new Thread(r);
Thread t2 = new Thread(r);
t1.start();
t2.start();
}
}
class Runner2 implements Runnable {
public void run() {
for(int i=0; i<30; i++) {
System.out.println("No. " + i);
}
}
}
被10整除就停顿2s:
public class TestThread3{
public static void main(String args[]) {
Runner3 r = new Runner3();
Thread t = new Thread(r);
t.start();
}
}
class Runner3 implements Runnable {
public void run() {
for(int i=0; i<30; i++) {
if(i%10==0 && i!=0) {
try{
Thread.sleep(2000);
}catch(InterruptedException e){}
}
System.out.println("No. " + i);
}
}
}
如何恰当的结束线程, 用flag:
public class TestThread4 {
public static void main(String args[]){
Runner4 r = new Runner4();
Thread t = new Thread(r);
t.start();
for(int i=0;i<100000;i++){
if(i%10000==0 & i>0)
System.out.println("in thread main i=" + i);
}
System.out.println("Thread main is over");
r.shutDown();
//t.stop();
}
}
class Runner4 implements Runnable {
private boolean flag=true;
public void run() {
int i = 0;
while (flag==true) {
System.out.print(" " + i++);
}
}
public void shutDown() {
flag = false;
}
}
isAlive:
public class TestThread6 {
public static void main(String args[]){
Thread t = new Runner6();
t.start();
for(int i=0; i<50; i++) {
System.out.println("MainThread: " + i);
}
}
}
class Runner6 extends Thread {
public void run() {
System.out.println(Thread.currentThread().isAlive());
for(int i=0;i<50;i++) {
System.out.println("SubThread: " + i);
}
}
}
线程同步: synchronized:
执行方法的过程中当前对象被锁定, 这样对象控制一个过程, 别的线程不可打扰.
public class TestSync implements Runnable {
Timer timer = new Timer();
public static void main(String[] args) {
TestSync test = new TestSync();
Thread t1 = new Thread(test);
Thread t2 = new Thread(test);
t1.setName("t1");
t2.setName("t2");
t1.start();
t2.start();
}
public void run(){
timer.add(Thread.currentThread().getName());
}
}
class Timer{
private static int num = 0;
public synchronized void add(String name){ //执行方法的过程中锁定当前对象
//synchronized (this) { //方法不加同步的话, 可以用此方法体的方式锁定
num ++;
try {Thread.sleep(1);}
catch (InterruptedException e) {}
System.out.println(name+", 你是第"+num+"个使用timer的线程");
//}
}
}
结果:
不加synchronized的话, 就都显示2
t1, 你是第1个使用timer的线程 t2, 你是第2个使用timer的线程
用synchronize的时候会出现死锁的现象,比如线程A执行过程中,锁定某一个对象1. 另一个线程B锁定另一个对象2, 线程A 需要继续锁定对象2, 线程B需要锁定对象1, 就会发生死锁.
public class TestDeadLock implements Runnable {
public int flag = 1;
static Object o1 = new Object(), o2 = new Object();
public void run() {
System.out.println("flag=" + flag);
if(flag == 1) {
synchronized(o1) {
try {
Thread.sleep(500);
} catch (Exception e) {
e.printStackTrace();
}
synchronized(o2) {
System.out.println("1");
}
}
}
if(flag == 0) {
synchronized(o2) {
try {
Thread.sleep(500);
} catch (Exception e) {
e.printStackTrace();
}
synchronized(o1) {
System.out.println("0");
}
}
}
}
public static void main(String[] args) {
TestDeadLock td1 = new TestDeadLock();
TestDeadLock td2 = new TestDeadLock();
td1.flag = 1;
td2.flag = 0;
Thread t1 = new Thread(td1);
Thread t2 = new Thread(td2);
t1.start();
t2.start();
}
}
结果: 线程不动了:
flag=1 flag=0
线程锁死后, 别的方法还可以访问
public class TT implements Runnable {
int b = 100;
public synchronized void m1() throws Exception{
b = 1000;
Thread.sleep(5000);
System.out.println("b = " + b);
}
public void m2() {
System.out.println(b);
}
public void run() {
try {
m1();
} catch(Exception e) {
e.printStackTrace();
}
}
public static void main(String[] args) throws Exception {
TT tt = new TT();
Thread t = new Thread(tt);
t.start();
Thread.sleep(1000);
tt.m2();
}
}
结果:
1000 b = 1000
上例子改一下:
public class TT implements Runnable {
int b = 100;
public synchronized void m1() throws Exception{
b = 1000;
Thread.sleep(5000);
System.out.println("b = " + b);
}
public void m2() throws Exception {
Thread.sleep(2500);
b = 2000;
}
public void run() {
try {
m1();
} catch(Exception e) {
e.printStackTrace();
}
}
public static void main(String[] args) throws Exception {
TT tt = new TT();
Thread t = new Thread(tt);
t.start();
tt.m2();
System.out.println(tt.b);
}
}
结果:
2000 b = 2000
再改一下:
1. 先执行m2, 执行完后
2. m1 执行 b=1000;
3. 主线程执行 输出b
4. m1 执行 输出b=1000;
public class TT implements Runnable {
int b = 100;
public synchronized void m1() throws Exception{
b = 1000;
Thread.sleep(5000);
System.out.println("b = " + b);
}
public synchronized void m2() throws Exception {
Thread.sleep(2500);
b = 2000;
}
public void run() {
try {
m1();
} catch(Exception e) {
e.printStackTrace();
}
}
public static void main(String[] args) throws Exception {
TT tt = new TT();
Thread t = new Thread(tt);
t.start();
tt.m2();
System.out.println(tt.b);
}
}
结果:
1000
b = 1000
wait必须和synchronized同时出现, 不能单独使用wait, wait是object类的方法.
wait的时候锁不归我所有, sleep的时候, 还抱着锁.
wait后需要notify叫醒, 也是object类的方法
public class ProducerConsumer {
public static void main(String[] args) {
SyncStack ss = new SyncStack();
Producer p = new Producer(ss);
Consumer c = new Consumer(ss);
new Thread(p).start();
new Thread(c).start();
}
}
class WoTou {
int id;
WoTou(int id) {
this.id = id;
}
public String toString() {
return "WoTou : " + id;
}
}
class SyncStack {
int index = 0;
WoTou[] arrWT = new WoTou[6];
public synchronized void push(WoTou wt) {
while(index == arrWT.length) {
try {
this.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
this.notifyAll();
arrWT[index] = wt;
index ++;
}
public synchronized WoTou pop() {
while(index == 0) {
try {
this.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
this.notifyAll();
index--;
return arrWT[index];
}
}
class Producer implements Runnable {
SyncStack ss = null;
Producer(SyncStack ss) {
this.ss = ss;
}
public void run() {
for(int i=0; i<10; i++) {
WoTou wt = new WoTou(i);
ss.push(wt);
System.out.println("生产了：" + wt);
try {
Thread.sleep((int)(Math.random() * 200));
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
class Consumer implements Runnable {
SyncStack ss = null;
Consumer(SyncStack ss) {
this.ss = ss;
}
public void run() {
for(int i=0; i<10; i++) {
WoTou wt = ss.pop();
System.out.println("消费了: " + wt);
try {
Thread.sleep((int)(Math.random() * 1000));
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
