线程按序交替 线程按序交替package com.yanxizhu; import java.util.concurrent.locks.Condition; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock; /** * @description: 线程按序交替 * @date: 2022/3/19 14:47 * @version: 1.0 */ public class PrintInfo { public static void main(String[] args) { print print = new print(); new Thread(new Runnable() { @Override public void run() { for(int i=1;i<5;i++){ try { print.printA(i); } catch (InterruptedException e) { e.printStackTrace(); } } } },"A").start(); new Thread(new Runnable() { @Override public void run() { for(int i=1;i<5;i++){ try { print.printB(i); } catch (InterruptedException e) { e.printStackTrace(); } } } },"B").start(); new Thread(new Runnable() { @Override public void run() { for(int i=1;i<5;i++){ try { print.printC(i); } catch (InterruptedException e) { e.printStackTrace(); } } } },"C").start(); } } class print{ private int num =1; Lock lock = new ReentrantLock(); Condition condition1 = lock.newCondition(); Condition condition2 = lock.newCondition(); Condition condition3 = lock.newCondition(); public void printA(int i) throws InterruptedException { lock.lock(); try{ if(num != 1){ condition1.await(); } System.out.println("A=="+Thread.currentThread().getName()+"====i="+i); num=2; condition2.signal(); }finally { lock.unlock(); } } public void printB(int i) throws InterruptedException { lock.lock(); try{ if(num != 2){ condition2.await(); } System.out.println("B=="+Thread.currentThread().getName()+"====i="+i); num=3; condition3.signal(); }finally { lock.unlock(); } } public void printC(int i) throws InterruptedException { lock.lock(); try{ if(num != 3){ condition3.await(); } System.out.println("C=="+Thread.currentThread().getName()+"====i="+i); num=1; condition1.signal(); }finally { lock.unlock(); } } }打印结果：A==A====i=1 B==B====i=1 C==C====i=1 A==A====i=2 B==B====i=2 C==C====i=2 A==A====i=3 B==B====i=3 C==C====i=3 A==A====i=4 B==B====i=4 C==C====i=4

ReentrantLock显示锁 package com.yanxizhu; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock; /** * @description: ReentrantLock * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/3/19 12:37 * @version: 1.0 */ public class LockDemo { public static void main(String[] args) { titck titck = new titck(); new Thread(titck,"线程1").start(); new Thread(titck,"线程2").start(); new Thread(titck,"线程3").start(); } public static class titck implements Runnable{ Lock lock = new ReentrantLock(); private int titck = 100; @Override public void run() { while(true){ lock.lock(); try{ if(titck>0){ try { Thread.sleep(200); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("剩余票数："+--titck); } }finally { lock.unlock(); } } } } } synchronized:隐式锁1、同步代码块2、同步方法jdk1.5之后：显示锁3、同步锁Lock注意：是一个显示锁，需要通过lock()方法上锁，必须通过unlock()方法进行释放锁。

高并发中集合问题 第一代线程安全集合类Vector、Hashtable是怎么保证线程安排的：使用synchronized修饰方法缺点：效率低下第二代线程非安全集合类ArrayList、HashMap线程不安全，但是性能好，用来替代Vector、Hashtable使用ArrayList、HashMap，需要线程安全怎么办呢？使用Collections.synchronizedList（list）；Collections.synchronizedMap（m）；底层使用synchronized代码块锁虽然也是锁住了所有的代码，但是锁在方法里边，并所在方法外边性能可以理解为稍有提高吧。毕竟进方法本身就要分配资源的第三代线程安全集合类在大量并发情况下如何提高集合的效率和安全呢？java.util.concurrent.*ConcurrentHashMap：CopyOnWriteArrayList：CopyOnWriteArraySet：注意不是CopyOnWriteHashSet*底层大都采用Lock锁（1.8的ConcurrentHashMap不使用Lock锁），保证安全的同时，性能也很高。