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附录：集合主题 翻译更新至 队列
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‎docs/book/Appendix-Collection-Topics.md‎

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<!-- Queues -->
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## 队列
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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：
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```java
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// collectiontopics/QueueBehavior.java
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// Compares basic behavior
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import java.util.*;
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import java.util.stream.*;
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import java.util.concurrent.*;
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public class QueueBehavior {
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static Stream<String> strings() {
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return Arrays.stream(
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("one two three four five six seven " +
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"eight nine ten").split(" "));
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}
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static void test(int id, Queue<String> queue) {
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System.out.print(id + ": ");
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strings().map(queue::offer).count();
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while(queue.peek() != null)
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System.out.print(queue.remove() + " ");
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System.out.println();
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}
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public static void main(String[] args) {
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int count = 10;
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test(1, new LinkedList<>());
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test(2, new PriorityQueue<>());
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test(3, new ArrayBlockingQueue<>(count));
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test(4, new ConcurrentLinkedQueue<>());
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test(5, new LinkedBlockingQueue<>());
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test(6, new PriorityBlockingQueue<>());
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test(7, new ArrayDeque<>());
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test(8, new ConcurrentLinkedDeque<>());
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test(9, new LinkedBlockingDeque<>());
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test(10, new LinkedTransferQueue<>());
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test(11, new SynchronousQueue<>());
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}
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}
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/* Output:
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1: one two three four five six seven eight nine ten
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2: eight five four nine one seven six ten three two
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3: one two three four five six seven eight nine ten
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4: one two three four five six seven eight nine ten
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5: one two three four five six seven eight nine ten
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6: eight five four nine one seven six ten three two
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7: one two three four five six seven eight nine ten
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8: one two three four five six seven eight nine ten
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9: one two three four five six seven eight nine ten
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10: one two three four five six seven eight nine ten
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11:
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*/
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```
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**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。
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<!-- Priority Queues -->
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### 优先级队列
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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：
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```java
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// collectiontopics/ToDoList.java
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// A more complex use of PriorityQueue
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import java.util.*;
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class ToDoItem implements Comparable<ToDoItem> {
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private char primary;
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private int secondary;
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private String item;
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ToDoItem(String td, char pri, int sec) {
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primary = pri;
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secondary = sec;
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item = td;
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}
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@Override
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public int compareTo(ToDoItem arg) {
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if(primary > arg.primary)
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return +1;
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if(primary == arg.primary)
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if(secondary > arg.secondary)
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return +1;
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else if(secondary == arg.secondary)
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return 0;
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return -1;
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}
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@Override
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public String toString() {
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return Character.toString(primary) +
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secondary + ": " + item;
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}
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}
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class ToDoList {
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public static void main(String[] args) {
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PriorityQueue<ToDoItem> toDo =
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new PriorityQueue<>();
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toDo.add(new ToDoItem("Empty trash", 'C', 4));
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toDo.add(new ToDoItem("Feed dog", 'A', 2));
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toDo.add(new ToDoItem("Feed bird", 'B', 7));
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toDo.add(new ToDoItem("Mow lawn", 'C', 3));
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toDo.add(new ToDoItem("Water lawn", 'A', 1));
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toDo.add(new ToDoItem("Feed cat", 'B', 1));
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while(!toDo.isEmpty())
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System.out.println(toDo.remove());
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}
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}
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/* Output:
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A1: Water lawn
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A2: Feed dog
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B1: Feed cat
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B7: Feed bird
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C3: Mow lawn
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C4: Empty trash
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*/
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```
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这展示了通过优先级队列自动排序待办事项。
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<!-- Deque -->
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### 双端队列
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**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：
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```java
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// collectiontopics/SimpleDeques.java
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// Very basic test of Deques
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import java.util.*;
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import java.util.concurrent.*;
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import java.util.function.*;
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class CountString implements Supplier<String> {
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private int n = 0;
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CountString() {}
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CountString(int start) { n = start; }
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@Override
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public String get() {
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return Integer.toString(n++);
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}
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}
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public class SimpleDeques {
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static void test(Deque<String> deque) {
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CountString s1 = new CountString(),
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s2 = new CountString(20);
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for(int n = 0; n < 8; n++) {
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deque.offerFirst(s1.get());
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deque.offerLast(s2.get()); // Same as offer()
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}
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System.out.println(deque);
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String result = "";
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while(deque.size() > 0) {
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System.out.print(deque.peekFirst() + " ");
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result += deque.pollFirst() + " ";
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System.out.print(deque.peekLast() + " ");
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result += deque.pollLast() + " ";
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}
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System.out.println("\n" + result);
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}
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public static void main(String[] args) {
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int count = 10;
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System.out.println("LinkedList");
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test(new LinkedList<>());
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System.out.println("ArrayDeque");
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test(new ArrayDeque<>());
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System.out.println("LinkedBlockingDeque");
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test(new LinkedBlockingDeque<>(count));
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System.out.println("ConcurrentLinkedDeque");
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test(new ConcurrentLinkedDeque<>());
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}
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}
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/* Output:
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LinkedList
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[7, 6, 5, 4, 3, 2, 1, 0, 20, 21, 22, 23, 24, 25, 26,
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27]
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7 27 6 26 5 25 4 24 3 23 2 22 1 21 0 20
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7 27 6 26 5 25 4 24 3 23 2 22 1 21 0 20
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ArrayDeque
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[7, 6, 5, 4, 3, 2, 1, 0, 20, 21, 22, 23, 24, 25, 26,
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27]
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7 27 6 26 5 25 4 24 3 23 2 22 1 21 0 20
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7 27 6 26 5 25 4 24 3 23 2 22 1 21 0 20
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LinkedBlockingDeque
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[4, 3, 2, 1, 0, 20, 21, 22, 23, 24]
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4 24 3 23 2 22 1 21 0 20
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4 24 3 23 2 22 1 21 0 20
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ConcurrentLinkedDeque
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[7, 6, 5, 4, 3, 2, 1, 0, 20, 21, 22, 23, 24, 25, 26,
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27]
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7 27 6 26 5 25 4 24 3 23 2 22 1 21 0 20
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7 27 6 26 5 25 4 24 3 23 2 22 1 21 0 20
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*/
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```
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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。
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<!-- Understanding Maps -->
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## 理解Map

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