1、锁的分类

2、读写锁

读锁：共享锁
写锁：独占锁

3、代码01

class MyCache{
    private  volatile  Map<String,Object> map = new HashMap<>();
    private ReadWriteLock rwLock = new ReentrantReadWriteLock();

    public void put(String key,Object value){
        rwLock.writeLock().lock();
        try {
            System.out.println(Thread.currentThread().getName()
                    +"\t 开始写"+key+"!!!!!");
            Thread.sleep(300);
            map.put(key,value);
            System.out.println(Thread.currentThread().getName()
                    +"\t 写完了"+key+"*****");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }finally {
            rwLock.writeLock().unlock();
        }
    }
    public void get(String key){
        rwLock.readLock().lock();
        try {
            System.out.println(Thread.currentThread().getName()
                    +"\t 开始读"+key+"!!!!!");
            Thread.sleep(300);
            Object result = map.get(key);
            System.out.println(Thread.currentThread().getName()
                    +"\t 读完了"+result+"*****");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }finally {
            rwLock.readLock().unlock();
        }
    }
}

public class ReadWriteLockDemo {

    public static void main(String[] args) throws InterruptedException {
        MyCache myCache = new MyCache();
        for (int i = 1; i <=5 ; i++) {
            int num = i;
            new Thread(()->{
                myCache.put(String.valueOf(num),String.valueOf(num));
            },String.valueOf(i)).start();
        }

        TimeUnit.SECONDS.sleep(3);
        for (int i = 1; i <=5 ; i++) {
            int num = i;
            new Thread(()->{
                myCache.get(String.valueOf(num));
            },String.valueOf(i)).start();
        }
    }
}

4、代码02

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.TimeUnit;

class MyCache{
    private volatile Map<String,Object> map = new HashMap<>();
    public void put(String key,Object value){
        System.out.println(Thread.currentThread().getName()+"\t 正在写"+key);
        //暂停一会儿线程
        try {TimeUnit.MILLISECONDS.sleep(300);} catch (InterruptedException e) {e.printStackTrace(); }
        map.put(key,value);
        System.out.println(Thread.currentThread().getName()+"\t 写完了"+key);
    }

    public Object get(String key){
        Object result = null;
        System.out.println(Thread.currentThread().getName()+"\t 正在读"+key);
        try {TimeUnit.MILLISECONDS.sleep(300);} catch (InterruptedException e) {e.printStackTrace(); }
        result = map.get(key);
        System.out.println(Thread.currentThread().getName()+"\t 读完了"+result);
        return result;
    }
}
public class ReadWriteLockDemo {


    public static void main(String[] args) {
        MyCache myCache = new MyCache();

        for (int i = 1; i <= 5; i++) {
            final int num = i;
            new Thread(()->{
                myCache.put(num+"",num+"");
            },String.valueOf(i)).start();
        }
        for (int i = 1; i <= 5; i++) {
            final int num = i;
            new Thread(()->{
                myCache.get(num+"");
            },String.valueOf(i)).start();
        }

    }
}