java 线程的学习心得（知了堂Java线程详解）
java 线程的学习心得（知了堂Java线程详解）package com.cjg.xiancheng; public class threadDaemon { public static void main(String[] args) { me me = new me(); parents parents = new parents(); //设置守护线程 Thread thread = new Thread(me); thread.setDaemon(true); thread.start(); new Thread(parents).start(); } } class me implements Runnable{ @Override public void run() {
1、线程的状态
package com.cjg.xiancheng;
public class threadStop implements Runnable {
//如果不填 boolean的默认值为flase
private boolean flag=true;
@Override
public void run() {
int i =1;
while (flag){
System.out.println("****" i );
}
}
public void stop(){
this.flag=false;
}
public static void main(String[] args) {
threadStop threadStop = new threadStop();
new Thread(threadStop "me").start();
for (int i = 0; i < 1000; i ) {
System.out.println("main" i);
if (i==500){
threadStop.stop();
System.out.println("stop=============================================================================");
}
}
}
}
package com.cjg.xiancheng;
import java.text.SimpleDateFormat;
import java.util.Date;
public class threadTime {
public static void main(String[] args) throws InterruptedException {
f();
while (true){
//打印当前系统的时间
Date date = new Date(System.currentTimeMillis());
Thread.sleep(1000);
System.out.println(new SimpleDateFormat("yyyy--MM--dd HH:mm:ss").format(date));
}
}
public static void f() throws InterruptedException {
int i=10;
while (true){
Thread.sleep(100);
System.out.println(i--);
if (i==0)break;
}
}
}2、线程的礼让
package com.cjg.xiancheng;
public class threadYield {
public static void main(String[] args) {
didi didi = new didi();
new Thread(didi "一号弟弟").start(); new Thread(didi "二号弟弟").start();
}
}
class didi implements Runnable{
@Override
public void run() {
System.out.println(Thread.currentThread().getName() "start");
Thread.yield();
System.out.println(Thread.currentThread().getName() "end");
}
}
Join
◆Join合并线程，待此线程执行完成后，再执行其他线程，其他线程阻塞。
package com.cjg.xiancheng;
public class threadJoin implements Runnable {
@Override
public void run() {
for (int i = 0; i < 1000; i ) {
System.out.println(Thread.currentThread().getName() i);
}
}
public static void main(String[] args) throws InterruptedException {
threadJoin threadJoin = new threadJoin();
Thread thread = new Thread(threadJoin "vip");
thread.start(); //线程已经开始
for (int i = 0; i < 500; i ) {
System.out.println(Thread.currentThread().getName() i);
if (i==100){
//知道join线程结束都只执行join线程
thread.join();
}
}
}
}3、线程的状态的查看
package com.cjg.xiancheng;
public class threadStatus {
public static void main(String[] args) throws InterruptedException {
Thread thread =new Thread(()->{
for (int i = 0; i <5 ; i ) {
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println("============================================================================");
});
Thread.State state = thread.getState();
System.out.println(state);
thread.start();
while (state !=Thread.State.TERMINATED){
Thread.sleep(100);
state = thread.getState();
System.out.println(state);
}
}
}4、线程的优先级
优先级低只是意味着获得调度的概率低。并不是优先级低就不会被调用了。这都是看CPU的调度。
可能会造成性能倒置
package com.cjg.xiancheng;
public class threadMore {
public static void main(String[] args) {
System.out.println(Thread.currentThread().getName() "的" Thread.currentThread().getPriority());
more more = new more();
Thread thread = new Thread(more); Thread thread1 = new Thread(more); Thread thread2 = new Thread(more);
thread.setPriority(Thread.MAX_PRIORITY);
thread1.setPriority(4);
thread2.setPriority(Thread.MIN_PRIORITY);
thread.start(); thread1.start(); thread2.start();
}
}
class more implements Runnable{
@Override
public void run() {
System.out.println(Thread.currentThread().getName() "的" Thread.currentThread().getPriority());
}
}5、线程守护
◆线程分为用户线程和守护线程
◆虚拟机必须确保用户线程执行完毕
◆虚拟机不用等待守护线程执行完毕
◆如：后台记录操作日志、监控内存、垃圾回收等待……
package com.cjg.xiancheng;
public class threadDaemon {
public static void main(String[] args) {
me me = new me();
parents parents = new parents();
//设置守护线程
Thread thread = new Thread(me);
thread.setDaemon(true);
thread.start();
new Thread(parents).start();
}
}
class me implements Runnable{
@Override
public void run() {
while (true){
System.out.println("我守护着你");
}
}
}
class parents implements Runnable{
@Override
public void run() {
for (int i = 0; i <= 36500; i ) {
System.out.println("爸妈开心的活了" i);
}
System.out.println("happy end");
}
}6、线程同步并发
队列加锁，保证线程安全，对应sql数据库的回滚。
◆由于同一进程的多个线程共享同一块存储空间，在带来方便的同时，也带来了访问冲突问题，为了保证数据在方法中被访问时的正确性，在访问时加入锁机制synchronized，当一个线程获得对象的排它锁，独占资源，其他线程必须等待，使用后释放锁即可，存在以下问题：
◆一个线程持有锁会导致其他所有需要此锁的线程挂起；
◆在多线程竞争下，加锁、释放锁会导致比较多的上下文切换和调度延时，引 起性能问题；
◆如果一个优先级高的线程等待一个优先级低的线程释放锁，会导致优先级倒置，引起性能问题。
==每个线程在自己的工作内存交互，内存控制不当会造成数据不一致==
package com.cjg.xiancheng;
public class syn {
public static void main(String[] args) {
buy buy = new buy();
new Thread(buy "11111").start(); new Thread(buy "2222222222").start(); new Thread(buy "33333333333").start();
}
}
class buy implements Runnable{
private boolean flag=true;
private int tiket = 10;
@Override
public void run() {
while (flag){
try {
buyTikets();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
private synchronized void buyTikets() throws InterruptedException {
if (tiket<=0){
flag=false;
return;
}
System.out.println(Thread.currentThread().getName() "获得第" tiket-- "票");
Thread.sleep(100);
}
}
//之前加锁的是 this 如果加锁不为 this 用程序块代替 . 注意索的是谁 需要增删改的对象
synchronized (对象 obj){
}
