附录：集合主题翻译更新至队列

2026-08-23 22:43:28 +08:00 · 2019-07-28 11:32:53 +08:00
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 <!-- Queues -->
 ## 队列

+有许多 **Queue** 实现，其中大多数是为并发应用程序设计的。许多实现都是通过排序行为而不是性能来区分的。这是一个涉及大多数 **Queue** 实现的基本示例，包括基于并发的队列。队列将元素从一端放入并从另一端取出：
+
+```java
+// collectiontopics/QueueBehavior.java
+// Compares basic behavior
+import java.util.*;
+import java.util.stream.*;
+import java.util.concurrent.*;
+
+public class QueueBehavior {
+  static Stream<String> strings() {
+    return Arrays.stream(
+      ("one two three four five six seven " +
+       "eight nine ten").split(" "));
+  }
+  static void test(int id, Queue<String> queue) {
+    System.out.print(id + ": ");
+    strings().map(queue::offer).count();
+    while(queue.peek() != null)
+      System.out.print(queue.remove() + " ");
+    System.out.println();
+  }
+  public static void main(String[] args) {
+    int count = 10;
+    test(1, new LinkedList<>());
+    test(2, new PriorityQueue<>());
+    test(3, new ArrayBlockingQueue<>(count));
+    test(4, new ConcurrentLinkedQueue<>());
+    test(5, new LinkedBlockingQueue<>());
+    test(6, new PriorityBlockingQueue<>());
+    test(7, new ArrayDeque<>());
+    test(8, new ConcurrentLinkedDeque<>());
+    test(9, new LinkedBlockingDeque<>());
+    test(10, new LinkedTransferQueue<>());
+    test(11, new SynchronousQueue<>());
+  }
+}
+/* Output:
+1: one two three four five six seven eight nine ten
+2: eight five four nine one seven six ten three two
+3: one two three four five six seven eight nine ten
+4: one two three four five six seven eight nine ten
+5: one two three four five six seven eight nine ten
+6: eight five four nine one seven six ten three two
+7: one two three four five six seven eight nine ten
+8: one two three four five six seven eight nine ten
+9: one two three four five six seven eight nine ten
+10: one two three four five six seven eight nine ten
+11:
+*/
+```
+
+**Deque** 接口也继承自 **Queue** 。 除优先级队列外，**Queue** 按照元素的插入顺序生成元素。 在此示例中，**SynchronousQueue** 不会产生任何结果，因为它是一个阻塞队列，其中每个插入操作必须等待另一个线程执行相应的删除操作，反之亦然。
+
+<!-- Priority Queues -->
+### 优先级队列
+
+考虑一个待办事项列表，其中每个对象包含一个 **String** 以及主要和次要优先级值。通过实现 **Comparable** 接口来控制此待办事项列表的顺序：
+
+```java
+// collectiontopics/ToDoList.java
+// A more complex use of PriorityQueue
+import java.util.*;
+
+class ToDoItem implements Comparable<ToDoItem> {
+  private char primary;
+  private int secondary;
+  private String item;
+  ToDoItem(String td, char pri, int sec) {
+    primary = pri;
+    secondary = sec;
+    item = td;
+  }
+  @Override
+  public int compareTo(ToDoItem arg) {
+    if(primary > arg.primary)
+      return +1;
+    if(primary == arg.primary)
+      if(secondary > arg.secondary)
+        return +1;
+      else if(secondary == arg.secondary)
+        return 0;
+    return -1;
+  }
+  @Override
+  public String toString() {
+    return Character.toString(primary) +
+      secondary + ": " + item;
+  }
+}
+
+class ToDoList {
+  public static void main(String[] args) {
+    PriorityQueue<ToDoItem> toDo =
+      new PriorityQueue<>();
+    toDo.add(new ToDoItem("Empty trash", 'C', 4));
+    toDo.add(new ToDoItem("Feed dog", 'A', 2));
+    toDo.add(new ToDoItem("Feed bird", 'B', 7));
+    toDo.add(new ToDoItem("Mow lawn", 'C', 3));
+    toDo.add(new ToDoItem("Water lawn", 'A', 1));
+    toDo.add(new ToDoItem("Feed cat", 'B', 1));
+    while(!toDo.isEmpty())
+      System.out.println(toDo.remove());
+  }
+}
+/* Output:
+A1: Water lawn
+A2: Feed dog
+B1: Feed cat
+B7: Feed bird
+C3: Mow lawn
+C4: Empty trash
+*/
+```
+
+这展示了通过优先级队列自动排序待办事项。
+
+<!-- Deque -->
+### 双端队列
+
+**Deque** （双端队列）就像一个队列，但是可以从任一端添加和删除元素。 Java 6为 **Deque** 添加了一个显式接口。以下是对实现了 **Deque** 的类的最基本的 **Deque** 方法的测试：
+
+```java
+// collectiontopics/SimpleDeques.java
+// Very basic test of Deques
+import java.util.*;
+import java.util.concurrent.*;
+import java.util.function.*;
+
+class CountString implements Supplier<String> {
+  private int n = 0;
+  CountString() {}
+  CountString(int start) { n = start; }
+  @Override
+  public String get() {
+    return Integer.toString(n++);
+  }
+}
+
+public class SimpleDeques {
+  static void test(Deque<String> deque) {
+    CountString s1 = new CountString(),
+                s2 = new CountString(20);
+    for(int n = 0; n < 8; n++) {
+        deque.offerFirst(s1.get());
+        deque.offerLast(s2.get()); // Same as offer()
+    }
+    System.out.println(deque);
+    String result = "";
+    while(deque.size() > 0) {
+      System.out.print(deque.peekFirst() + " ");
+      result += deque.pollFirst() + " ";
+      System.out.print(deque.peekLast() + " ");
+      result += deque.pollLast() + " ";
+    }
+    System.out.println("\n" + result);
+  }
+  public static void main(String[] args) {
+    int count = 10;
+    System.out.println("LinkedList");
+    test(new LinkedList<>());
+    System.out.println("ArrayDeque");
+    test(new ArrayDeque<>());
+    System.out.println("LinkedBlockingDeque");
+    test(new LinkedBlockingDeque<>(count));
+    System.out.println("ConcurrentLinkedDeque");
+    test(new ConcurrentLinkedDeque<>());
+  }
+}
+/* Output:
+LinkedList
+[7, 6, 5, 4, 3, 2, 1, 0, 20, 21, 22, 23, 24, 25, 26,
+27]
+7 27 6 26 5 25 4 24 3 23 2 22 1 21 0 20
+7 27 6 26 5 25 4 24 3 23 2 22 1 21 0 20
+ArrayDeque
+[7, 6, 5, 4, 3, 2, 1, 0, 20, 21, 22, 23, 24, 25, 26,
+27]
+7 27 6 26 5 25 4 24 3 23 2 22 1 21 0 20
+7 27 6 26 5 25 4 24 3 23 2 22 1 21 0 20
+LinkedBlockingDeque
+[4, 3, 2, 1, 0, 20, 21, 22, 23, 24]
+4 24 3 23 2 22 1 21 0 20
+4 24 3 23 2 22 1 21 0 20
+ConcurrentLinkedDeque
+[7, 6, 5, 4, 3, 2, 1, 0, 20, 21, 22, 23, 24, 25, 26,
+27]
+7 27 6 26 5 25 4 24 3 23 2 22 1 21 0 20
+7 27 6 26 5 25 4 24 3 23 2 22 1 21 0 20
+*/
+```
+
+我只使用了 **Deque** 方法的“offer”和“poll”版本，因为当 **LinkedBlockingDeque** 的大小有限时，这些方法不会抛出异常。请注意， **LinkedBlockingDeque** 仅填充到它的限制大小为止，然后忽略额外的添加。

 <!-- Understanding Maps -->
 ## 理解Map