说到队列:它是链表结构
什么时候会阻塞队列呢?如下图所示
阻塞:队列
首先我们看看阻塞队列类中的结构:
由上图可知阻塞队列和set list同等地位,故也十分重要
所以说BlockingQueue不是新的东西
问:什么时候我们会使用阻塞队列?
答:多线程,线程池多线程并发处理,线程池
Blockingdeque:双端队列:两头都可操作,能返回值
学会使用队列:
添加,移除
四组API
方式 | 抛出异常 | 不会抛出异常,有返回值 | 阻塞等待 | 超时等待 |
---|---|---|---|---|
添加 | add() | offer() | put() | offer(“d”, 2, TimeUnit.SECONDS) |
移除 | remove() | poll() | take() | poll(2,TimeUnit.SECONDS) |
检测队列首 | element() | peek() | – | – |
System.out.println(blockingQueue.element());//返回队首元素
System.out.println(blockingQueue.peek());//检测队首元素
1.代码抛出异常
package com.Blockqueue;
import java.util.Collection;
import java.util.Collections;
import java.util.concurrent.ArrayBlockingQueue;
public class Test {
public static void main(String[] args) {
//抛出异常
test1();
}
public static void test1(){
//队列的大小
//Exception in thread "main" java.lang.IllegalStateException: Queue full
// System.out.println(blockingQueue.add("d"));
ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);
System.out.println(blockingQueue.add("a"));
System.out.println(blockingQueue.add("b"));
System.out.println(blockingQueue.add("c"));
System.out.println("===============================");
System.out.println(blockingQueue.remove());
System.out.println(blockingQueue.remove());
System.out.println(blockingQueue.remove());
System.out.println(blockingQueue.remove());
//队列中只有三个值,但是移除了四次,则会抛出异常
//Exception in thread "main" java.util.NoSuchElementException
}
}
2.不会抛出异常
代码:
public static void test2() {
ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);
System.out.println(blockingQueue.offer("a"));
System.out.println(blockingQueue.offer("b"));
System.out.println(blockingQueue.offer("c"));
//System.out.println(blockingQueue.offer("d"));
System.out.println("============================");
System.out.println(blockingQueue.poll());
System.out.println(blockingQueue.poll());
System.out.println(blockingQueue.poll());
System.out.println(blockingQueue.poll());
}
超过队列中的最大容量会返回false:
队列中没有元素了,但还是选择弹出,会返回null
3.阻塞等待
public static void test3() throws InterruptedException {
ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);
blockingQueue.put("a");
blockingQueue.put("b");
blockingQueue.put("c");
// blockingQueue.put("d");//队列没有位置了,一直阻塞
System.out.println("========================");
System.out.println(blockingQueue.take());
System.out.println(blockingQueue.take());
System.out.println(blockingQueue.take());
System.out.println(blockingQueue.take());
}
/**
* 等待,阻塞(一直阻塞)
*
* 等待,阻塞(等待超时)
/
}
如果容量为3放了4个,会一直阻塞队列
只要三个,取了4次.会一直阻塞队列
4.超时等待
public static void test4()throws InterruptedException{
ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);
System.out.println(blockingQueue.offer("a"));
System.out.println(blockingQueue.offer("b"));
System.out.println(blockingQueue.offer("c"));
System.out.println(blockingQueue.offer("d", 2, TimeUnit.SECONDS));//等待超过2秒就退出
System.out.println("=================================");
System.out.println(blockingQueue.poll());
System.out.println(blockingQueue.poll());
System.out.println(blockingQueue.poll());
System.out.println(blockingQueue.poll(2,TimeUnit.SECONDS));
}
package com.Blockqueue;
import java.util.Collection;
import java.util.Collections;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingDeque;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.TimeUnit;
public class Test {
public static void main(String[] args) throws InterruptedException {
//抛出异常
test4();
}
public static void test1(){
//队列的大小
//Exception in thread "main" java.lang.IllegalStateException: Queue full
// System.out.println(blockingQueue.add("d"));
ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);
System.out.println(blockingQueue.add("a"));
System.out.println(blockingQueue.add("b"));
System.out.println(blockingQueue.add("c"));
System.out.println(blockingQueue.element());
System.out.println("===============================");
System.out.println(blockingQueue.remove());
System.out.println(blockingQueue.remove());
System.out.println(blockingQueue.remove());
System.out.println(blockingQueue.remove());
//队列中只有三个值,但是移除了四次,则会抛出异常
//Exception in thread "main" java.util.NoSuchElementException
}
public static void test2() {
ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);
System.out.println(blockingQueue.offer("a"));
System.out.println(blockingQueue.offer("b"));
System.out.println(blockingQueue.offer("c"));
//System.out.println(blockingQueue.offer("d"));
System.out.println("============================");
System.out.println(blockingQueue.poll());
System.out.println(blockingQueue.poll());
System.out.println(blockingQueue.poll());
System.out.println(blockingQueue.poll());
}
public static void test3() throws InterruptedException {
ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);
blockingQueue.put("a");
blockingQueue.put("b");
blockingQueue.put("c");
// blockingQueue.put("d");//队列没有位置了,一直阻塞
System.out.println("========================");
System.out.println(blockingQueue.take());
System.out.println(blockingQueue.take());
System.out.println(blockingQueue.take());
System.out.println(blockingQueue.take());
}
/**
* 等待,阻塞(一直阻塞)
*
* 等待,阻塞(等待超时)
/
public static void test4()throws InterruptedException{
ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);
System.out.println(blockingQueue.offer("a"));
System.out.println(blockingQueue.offer("b"));
System.out.println(blockingQueue.offer("c"));
System.out.println(blockingQueue.offer("d", 2, TimeUnit.SECONDS));//等待超过2秒就退出
System.out.println("=================================");
System.out.println(blockingQueue.poll());
System.out.println(blockingQueue.poll());
System.out.println(blockingQueue.poll());
System.out.println(blockingQueue.poll(2,TimeUnit.SECONDS));
}
}
SynchronousQueue:同步队列
没有容量,进去一个元素,必须等待取出来之后,才能往里面放一个元素!
put(),take().
package com;
import java.util.concurrent.BlockingDeque;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.SynchronousQueue;
import java.util.concurrent.TimeUnit;
/**
* 同步队列
* 和其他的BlockingQueue不一样,synchronizequeue不存储元素
* put了一个元素,必须从里面先take出来才能继续放,否则不能再put进去值
* 如果连续put三个值进去就只进去一个值,其他值进不去,进而阻塞队列
*/
public class SynchronousQueueDemo01 {
public static void main(String[] args) throws InterruptedException {
BlockingQueue<String> blockingqueue = new SynchronousQueue<>();//同步队列
new Thread(()->{
try {
System.out.println(Thread.currentThread().getName()+":put 1");
blockingqueue.put("1");
System.out.println(Thread.currentThread().getName()+":put 2");
blockingqueue.put("2");
System.out.println(Thread.currentThread().getName()+":put 3");
blockingqueue.put("3");
} catch (InterruptedException e) {
e.printStackTrace();
}
},Thread.currentThread().getName()).start();
new Thread(()->{
try {
TimeUnit.SECONDS.sleep(3);
System.out.println(Thread.currentThread().getName()+"取出了"+blockingqueue.take());
TimeUnit.SECONDS.sleep(3);
System.out.println(Thread.currentThread().getName()+"取出了"+blockingqueue.take());
TimeUnit.SECONDS.sleep(3);
System.out.println(Thread.currentThread().getName()+"取出了"+blockingqueue.take());
} catch (InterruptedException e) {
e.printStackTrace();
}
}).start();
}
}
笔记自己看视频做的,视频链接如下:
B站地址:https://space.bilibili.com/95256449