这次讲解的是BlockingQueue：
BlockingQueue（阻塞队列）是什么？
当队列为空时，从队列中获取元素将阻塞。
当队列为满时，从队列中添加元素将阻塞。
因为是队列，所以我们理应想到先进先出。
接下来我们来演示简单的使用一下：
add（抛出异常）：
/**
* @author Cocowwy
* @create 2020-05-05-14:53
*/
public class BlockingQueueDemo {
public static void main(String[] args) {
BlockingQueue<String> 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.add("x"));
}
}
结果如下：
true
true
true
Exception in thread "main" java.lang.IllegalStateException: Queue full
at java.util.AbstractQueue.add(AbstractQueue.java:98)
at java.util.concurrent.ArrayBlockingQueue.add(ArrayBlockingQueue.java:312)
at juc.BlockingQueueDemo.main(BlockingQueueDemo.java:16)
我们可以看到如果添加的元素大于3之后，即当队列满了之后会抛异常：java.lang.IllegalStateException: Queue full
remove（抛出异常）：
public class BlockingQueueDemo {
public static void main(String[] args) {
BlockingQueue<String> 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.add("x"));
System.out.println(blockingQueue.remove()); //返回值是E（即对象） 因为是队列 所以是a
System.out.println(blockingQueue.remove());
System.out.println(blockingQueue.remove());
System.out.println(blockingQueue.remove());
}
}
这里需要注意的是remove的返回类型是E（对象）
结果如下：
true
true
true
a
b
c
Exception in thread "main" java.util.NoSuchElementException
at java.util.AbstractQueue.remove(AbstractQueue.java:117)
at juc.BlockingQueueDemo.main(BlockingQueueDemo.java:20)
Process finished with exit code 1
我们可以看到如果添加的元素大于3之后，即当队列空了之后再删会抛异常：java.util.NoSuchElementException
element（抛出异常）：
public class BlockingQueueDemo {
public static void main(String[] args) {
BlockingQueue<String> 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());
}
}
结果如下：
true
true
true
a
检查队首元素是什么
offer（特殊值）：
public class BlockingQueueDemo {
public static void main(String[] args) {
BlockingQueue<String> 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"));
}
}
结果如下：
true
true
true
false
插入，返回成功
pull（特殊值）：
public class BlockingQueueDemo {
public static void main(String[] args) {
BlockingQueue<String> 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.poll());
System.out.println(blockingQueue.poll());
System.out.println(blockingQueue.poll());
System.out.println(blockingQueue.poll());
}
}
结果如下：
true
true
true
a
b
c
null
peek（特殊值）：
public class BlockingQueueDemo {
public static void main(String[] args) {
BlockingQueue<String> 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.peek());
}
}
结果如下：
true
true
true
a
put（阻塞）：
public class BlockingQueueDemo {
public static void main(String[] args) throws InterruptedException {
BlockingQueue<String> blockingQueue=new ArrayBlockingQueue<>(3);
blockingQueue.put("a");
blockingQueue.put("b");
blockingQueue.put("c");
blockingQueue.put("d");
}
}
结果如下：
就是啥都没有一片空白，因为此时一直阻塞，等待，与接下来的take进行对比
take（阻塞）：
public class BlockingQueueDemo {
public static void main(String[] args) throws InterruptedException {
BlockingQueue<String> blockingQueue=new ArrayBlockingQueue<>(3);
blockingQueue.put("a");
blockingQueue.put("b");
blockingQueue.put("c");
System.out.println(blockingQueue.take());
blockingQueue.put("e");
System.out.println(blockingQueue.take());
System.out.println(blockingQueue.take());
System.out.println(blockingQueue.take());
}
}
结果如下：
a
b
c
e
与上面的put对比一下，这里abc添加进去后如果想加e是加不进去的，会阻塞，而take进行取出后就能加入e了
offer（超时）：
public class BlockingQueueDemo {
public static void main(String[] args) throws InterruptedException {
BlockingQueue<String> 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", 3L, TimeUnit.SECONDS));
}
}
结果如下：
true
true
true
false //等待了3s
让其等待3s，返回值为boolean
poll（超时）：
public class BlockingQueueDemo {
public static void main(String[] args) throws InterruptedException {
BlockingQueue<String> 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.poll());
System.out.println(blockingQueue.poll());
System.out.println(blockingQueue.poll());
System.out.println(blockingQueue.poll(3L, TimeUnit.SECONDS));
}
}
结果如下：
true
true
true
a
b
c
null //等待了3s
综合上述情况我们可以得到此图：
