這次講解的是BlockingQueue:
BlockingQueue(阻塞隊列)是什麼?
當隊列爲空時,從隊列中獲取元素將阻塞。
當隊列爲滿時,從隊列中添加元素將阻塞。
因爲是隊列,所以我們理應想到先進先出。
接下來我們來演示簡單的使用一下:
add(拋出異常):
/**
* @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"));
}
}
結果如下:
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)
我們可以看到如果添加的元素大於3之後,即當隊列滿了之後會拋異常:java.lang.IllegalStateException: Queue full
remove(拋出異常):
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(即對象) 因爲是隊列 所以是a
System.out.println(blockingQueue.remove());
System.out.println(blockingQueue.remove());
System.out.println(blockingQueue.remove());
}
}
這裏需要注意的是remove的返回類型是E(對象)
結果如下:
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
我們可以看到如果添加的元素大於3之後,即當隊列空了之後再刪會拋異常:java.util.NoSuchElementException
element(拋出異常):
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());
}
}
結果如下:
true
true
true
a
檢查隊首元素是什麼
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"));
}
}
結果如下:
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());
}
}
結果如下:
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());
}
}
結果如下:
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");
}
}
結果如下:
就是啥都沒有一片空白,因爲此時一直阻塞,等待,與接下來的take進行對比
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());
}
}
結果如下:
a
b
c
e
與上面的put對比一下,這裏abc添加進去後如果想加e是加不進去的,會阻塞,而take進行取出後就能加入e了
offer(超時):
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));
}
}
結果如下:
true
true
true
false //等待了3s
讓其等待3s,返回值爲boolean
poll(超時):
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));
}
}
結果如下:
true
true
true
a
b
c
null //等待了3s
綜合上述情況我們可以得到此圖: