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附录：集合主题 翻译更新至 填充集合
This commit is contained in:
1326670425
@@ -362,23 +362,453 @@ Cyan
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可以看到，使用 **LinkedHashMap** 确实能够保留 **HTMLColors.ARRAY** 的顺序。
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<!-- List Behavior -->
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## List表现
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## List行为
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**Lists** 是存储和检索对象（次于数组）的最基本方法。基本列表操作包括：
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- **add()** 用于插入元素
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- **get()** 用于随机访问元素
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- **iterator()** 获取序列上的一个 **Iterator**
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- **stream()** 生成元素的一个 **Stream**
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列表构造方法始终保留元素的添加顺序。
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以下示例中的方法各自涵盖了一组不同的行为：每个 **List** 可以执行的操作（ **basicTest()** ），使用 **Iterator** （ **iterMotion()** ）遍历序列，使用 **Iterator** （ **iterManipulation()** ）更改内容，查看 **List** 操作（ **testVisual()** ）的效果，以及仅可用于 **LinkedLists** 的操作：
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```java
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// collectiontopics/ListOps.java
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// Things you can do with Lists
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import java.util.*;
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import onjava.HTMLColors;
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public class ListOps {
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// Create a short list for testing:
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static final List<String> LIST =
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HTMLColors.LIST.subList(0, 10);
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private static boolean b;
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private static String s;
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private static int i;
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private static Iterator<String> it;
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private static ListIterator<String> lit;
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public static void basicTest(List<String> a) {
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a.add(1, "x"); // Add at location 1
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a.add("x"); // Add at end
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// Add a collection:
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a.addAll(LIST);
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// Add a collection starting at location 3:
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a.addAll(3, LIST);
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b = a.contains("1"); // Is it in there?
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// Is the entire collection in there?
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b = a.containsAll(LIST);
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// Lists allow random access, which is cheap
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// for ArrayList, expensive for LinkedList:
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s = a.get(1); // Get (typed) object at location 1
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i = a.indexOf("1"); // Tell index of object
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b = a.isEmpty(); // Any elements inside?
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it = a.iterator(); // Ordinary Iterator
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lit = a.listIterator(); // ListIterator
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lit = a.listIterator(3); // Start at location 3
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i = a.lastIndexOf("1"); // Last match
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a.remove(1); // Remove location 1
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a.remove("3"); // Remove this object
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a.set(1, "y"); // Set location 1 to "y"
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// Keep everything that's in the argument
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// (the intersection of the two sets):
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a.retainAll(LIST);
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// Remove everything that's in the argument:
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a.removeAll(LIST);
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i = a.size(); // How big is it?
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a.clear(); // Remove all elements
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}
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public static void iterMotion(List<String> a) {
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ListIterator<String> it = a.listIterator();
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b = it.hasNext();
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b = it.hasPrevious();
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s = it.next();
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i = it.nextIndex();
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s = it.previous();
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i = it.previousIndex();
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}
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public static void iterManipulation(List<String> a) {
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ListIterator<String> it = a.listIterator();
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it.add("47");
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// Must move to an element after add():
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it.next();
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// Remove the element after the new one:
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it.remove();
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// Must move to an element after remove():
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it.next();
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// Change the element after the deleted one:
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it.set("47");
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}
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public static void testVisual(List<String> a) {
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System.out.println(a);
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List<String> b = LIST;
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System.out.println("b = " + b);
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a.addAll(b);
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a.addAll(b);
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System.out.println(a);
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// Insert, remove, and replace elements
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// using a ListIterator:
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ListIterator<String> x =
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a.listIterator(a.size()/2);
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x.add("one");
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System.out.println(a);
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System.out.println(x.next());
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x.remove();
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System.out.println(x.next());
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x.set("47");
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System.out.println(a);
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// Traverse the list backwards:
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x = a.listIterator(a.size());
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while(x.hasPrevious())
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System.out.print(x.previous() + " ");
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System.out.println();
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System.out.println("testVisual finished");
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}
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// There are some things that only LinkedLists can do:
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public static void testLinkedList() {
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LinkedList<String> ll = new LinkedList<>();
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ll.addAll(LIST);
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System.out.println(ll);
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// Treat it like a stack, pushing:
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ll.addFirst("one");
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ll.addFirst("two");
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System.out.println(ll);
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// Like "peeking" at the top of a stack:
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System.out.println(ll.getFirst());
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// Like popping a stack:
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System.out.println(ll.removeFirst());
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System.out.println(ll.removeFirst());
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// Treat it like a queue, pulling elements
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// off the tail end:
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System.out.println(ll.removeLast());
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System.out.println(ll);
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}
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public static void main(String[] args) {
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// Make and fill a new list each time:
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basicTest(new LinkedList<>(LIST));
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basicTest(new ArrayList<>(LIST));
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iterMotion(new LinkedList<>(LIST));
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iterMotion(new ArrayList<>(LIST));
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iterManipulation(new LinkedList<>(LIST));
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iterManipulation(new ArrayList<>(LIST));
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testVisual(new LinkedList<>(LIST));
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testLinkedList();
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}
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}
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/* Output:
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[AliceBlue, AntiqueWhite, Aquamarine, Azure, Beige,
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Bisque, Black, BlanchedAlmond, Blue, BlueViolet]
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b = [AliceBlue, AntiqueWhite, Aquamarine, Azure, Beige,
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Bisque, Black, BlanchedAlmond, Blue, BlueViolet]
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[AliceBlue, AntiqueWhite, Aquamarine, Azure, Beige,
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Bisque, Black, BlanchedAlmond, Blue, BlueViolet,
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AliceBlue, AntiqueWhite, Aquamarine, Azure, Beige,
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Bisque, Black, BlanchedAlmond, Blue, BlueViolet,
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AliceBlue, AntiqueWhite, Aquamarine, Azure, Beige,
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Bisque, Black, BlanchedAlmond, Blue, BlueViolet]
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[AliceBlue, AntiqueWhite, Aquamarine, Azure, Beige,
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Bisque, Black, BlanchedAlmond, Blue, BlueViolet,
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AliceBlue, AntiqueWhite, Aquamarine, Azure, Beige, one,
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Bisque, Black, BlanchedAlmond, Blue, BlueViolet,
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AliceBlue, AntiqueWhite, Aquamarine, Azure, Beige,
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Bisque, Black, BlanchedAlmond, Blue, BlueViolet]
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Bisque
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Black
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[AliceBlue, AntiqueWhite, Aquamarine, Azure, Beige,
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Bisque, Black, BlanchedAlmond, Blue, BlueViolet,
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AliceBlue, AntiqueWhite, Aquamarine, Azure, Beige, one,
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47, BlanchedAlmond, Blue, BlueViolet, AliceBlue,
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AntiqueWhite, Aquamarine, Azure, Beige, Bisque, Black,
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BlanchedAlmond, Blue, BlueViolet]
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BlueViolet Blue BlanchedAlmond Black Bisque Beige Azure
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Aquamarine AntiqueWhite AliceBlue BlueViolet Blue
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BlanchedAlmond 47 one Beige Azure Aquamarine
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AntiqueWhite AliceBlue BlueViolet Blue BlanchedAlmond
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Black Bisque Beige Azure Aquamarine AntiqueWhite
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AliceBlue
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testVisual finished
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[AliceBlue, AntiqueWhite, Aquamarine, Azure, Beige,
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Bisque, Black, BlanchedAlmond, Blue, BlueViolet]
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[two, one, AliceBlue, AntiqueWhite, Aquamarine, Azure,
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Beige, Bisque, Black, BlanchedAlmond, Blue, BlueViolet]
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two
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two
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one
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BlueViolet
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[AliceBlue, AntiqueWhite, Aquamarine, Azure, Beige,
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Bisque, Black, BlanchedAlmond, Blue]
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*/
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```
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在 **basicTest()** 和 **iterMotion()** 中，方法调用是为了展示正确的语法，尽管获取了返回值，但不会使用它。在某些情况下，根本不会去获取返回值。在使用这些方法之前，请查看JDK文档中这些方法的完整用法。
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<!-- Set Behavior -->
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## Set表现
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## Set行为
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**Set** 的主要用处是测试成员身份，不过也可以将其用作删除重复元素的工具。如果不关心元素顺序或并发性， **HashSet** 总是最好的选择，因为它是专门为了快速查找而设计的（这里使用了在[附录：理解equals和hashCode方法]()章节中探讨的散列函数）。
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其它的 **Set** 实现产生不同的排序行为：
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```java
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// collectiontopics/SetOrder.java
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import java.util.*;
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import onjava.HTMLColors;
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public class SetOrder {
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static String[] sets = {
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"java.util.HashSet",
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"java.util.TreeSet",
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"java.util.concurrent.ConcurrentSkipListSet",
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"java.util.LinkedHashSet",
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"java.util.concurrent.CopyOnWriteArraySet",
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};
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static final List<String> RLIST =
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new ArrayList<>(HTMLColors.LIST);
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static {
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Collections.reverse(RLIST);
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}
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public static void
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main(String[] args) throws Exception {
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for(String type: sets) {
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System.out.format("[-> %s <-]%n",
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type.substring(type.lastIndexOf('.') + 1));
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@SuppressWarnings("unchecked")
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Set<String> set = (Set<String>)
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Class.forName(type).newInstance();
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set.addAll(RLIST);
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set.stream()
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.limit(10)
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.forEach(System.out::println);
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}
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}
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}
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/* Output:
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[-> HashSet <-]
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MediumOrchid
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PaleGoldenRod
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Sienna
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LightSlateGray
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DarkSeaGreen
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Black
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Gainsboro
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Orange
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LightCoral
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DodgerBlue
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[-> TreeSet <-]
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AliceBlue
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AntiqueWhite
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Aquamarine
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Azure
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Beige
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Bisque
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Black
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BlanchedAlmond
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Blue
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BlueViolet
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[-> ConcurrentSkipListSet <-]
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AliceBlue
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AntiqueWhite
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Aquamarine
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Azure
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Beige
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Bisque
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Black
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BlanchedAlmond
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Blue
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BlueViolet
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[-> LinkedHashSet <-]
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YellowGreen
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Yellow
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WhiteSmoke
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White
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Wheat
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Violet
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Turquoise
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Tomato
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Thistle
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Teal
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[-> CopyOnWriteArraySet <-]
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YellowGreen
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Yellow
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WhiteSmoke
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White
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Wheat
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Violet
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Turquoise
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Tomato
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Thistle
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Teal
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*/
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```
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这里需要使用 **@SuppressWarnings(“unchecked”)** ，因为这里将一个 **String** （可能是任何东西）传递给了 **Class.forName(type).newInstance()** 。编译器并不能保证这是一次成功的操作。
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**RLIST** 是 **HTMLColors.LIST** 的反转版本。因为 **Collections.reverse()** 是通过修改参数来执行反向操作，而不是返回包含反向元素的新 **List** ，所以该调用在 **static** 块内执行。 **RLIST** 可以防止我们意外地认为 **Set** 对其结果进行了排序。
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**HashSet** 的输出结果似乎没有可辨别的顺序，因为它是基于散列函数的。 **TreeSet** 和 **ConcurrentSkipListSet** 都对它们的元素进行了排序，它们都实现了 **SortedSet** 接口来标识这个特点。因为实现该接口的 **Set** 按顺序排列，所以该接口还有一些其他的可用操作。 **LinkedHashSet** 和 **CopyOnWriteArraySet** 尽管没有用于标识的接口，但它们还是保留了元素的插入顺序。
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**ConcurrentSkipListSet** 和 **CopyOnWriteArraySet** 是线程安全的。
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在附录的最后，我们将了解在非 **HashSet** 实现的 **Set** 上添加额外排序的性能成本，以及不同实现中的任何其他功能的成本。
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<!-- Using Functional Operations with any Map -->
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## 在Map中使用函数式操作
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与 **Collection** 接口一样，**forEach()** 也内置在 **Map** 接口中。但是如果想要执行任何其他的基本功能操作，比如 **map()** ，**flatMap()** ，**reduce()** 或 **filter()** 时，该怎么办？ 查看 **Map** 接口发现并没有这些。
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可以通过 **entrySet()** 连接到这些方法，该方法会生成一个由 **Map.Entry** 对象组成的 **Set** 。这个 **Set** 包含 **stream()** 和 **parallelStream()** 方法。只需要记住一件事，这里正在使用的是 **Map.Entry** 对象：
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```java
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// collectiontopics/FunctionalMap.java
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// Functional operations on a Map
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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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import static onjava.HTMLColors.*;
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public class FunctionalMap {
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public static void main(String[] args) {
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MAP.entrySet().stream()
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.map(Map.Entry::getValue)
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.filter(v -> v.startsWith("Dark"))
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.map(v -> v.replaceFirst("Dark", "Hot"))
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.forEach(System.out::println);
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}
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}
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/* Output:
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HotBlue
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HotCyan
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HotGoldenRod
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HotGray
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HotGreen
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HotKhaki
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HotMagenta
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HotOliveGreen
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HotOrange
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HotOrchid
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HotRed
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HotSalmon
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HotSeaGreen
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HotSlateBlue
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HotSlateGray
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HotTurquoise
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HotViolet
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*/
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```
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生成 **Stream** 后，所有的基本功能方法，甚至更多就都可以使用了。
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<!-- Selecting Parts of a Map -->
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## 选择Map的部分
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## 选择Map片段
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由 **TreeMap** 和 **ConcurrentSkipListMap** 实现的 **NavigableMap** 接口解决了需要选择Map片段的问题。下面是一个示例，使用了 **HTMLColors** ：
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```java
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// collectiontopics/NavMap.java
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// NavigableMap produces pieces of a Map
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import java.util.*;
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import java.util.concurrent.*;
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import static onjava.HTMLColors.*;
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public class NavMap {
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public static final
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NavigableMap<Integer,String> COLORS =
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new ConcurrentSkipListMap<>(MAP);
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public static void main(String[] args) {
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show(COLORS.firstEntry());
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border();
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show(COLORS.lastEntry());
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border();
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NavigableMap<Integer, String> toLime =
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COLORS.headMap(rgb("Lime"), true);
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show(toLime);
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border();
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show(COLORS.ceilingEntry(rgb("DeepSkyBlue") - 1));
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border();
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show(COLORS.floorEntry(rgb("DeepSkyBlue") - 1));
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border();
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show(toLime.descendingMap());
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border();
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show(COLORS.tailMap(rgb("MistyRose"), true));
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border();
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show(COLORS.subMap(
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rgb("Orchid"), true,
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rgb("DarkSalmon"), false));
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}
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}
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/* Output:
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||||
0x000000: Black
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||||
******************************
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||||
0xFFFFFF: White
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||||
******************************
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||||
0x000000: Black
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0x000080: Navy
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0x00008B: DarkBlue
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0x0000CD: MediumBlue
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0x0000FF: Blue
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0x006400: DarkGreen
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0x008000: Green
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||||
0x008080: Teal
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0x008B8B: DarkCyan
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||||
0x00BFFF: DeepSkyBlue
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0x00CED1: DarkTurquoise
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||||
0x00FA9A: MediumSpringGreen
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||||
0x00FF00: Lime
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******************************
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||||
0x00BFFF: DeepSkyBlue
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||||
******************************
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||||
0x008B8B: DarkCyan
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||||
******************************
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||||
0x00FF00: Lime
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||||
0x00FA9A: MediumSpringGreen
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||||
0x00CED1: DarkTurquoise
|
||||
0x00BFFF: DeepSkyBlue
|
||||
0x008B8B: DarkCyan
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||||
0x008080: Teal
|
||||
0x008000: Green
|
||||
0x006400: DarkGreen
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||||
0x0000FF: Blue
|
||||
0x0000CD: MediumBlue
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||||
0x00008B: DarkBlue
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||||
0x000080: Navy
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||||
0x000000: Black
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||||
******************************
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||||
0xFFE4E1: MistyRose
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||||
0xFFEBCD: BlanchedAlmond
|
||||
0xFFEFD5: PapayaWhip
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||||
0xFFF0F5: LavenderBlush
|
||||
0xFFF5EE: SeaShell
|
||||
0xFFF8DC: Cornsilk
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||||
0xFFFACD: LemonChiffon
|
||||
0xFFFAF0: FloralWhite
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||||
0xFFFAFA: Snow
|
||||
0xFFFF00: Yellow
|
||||
0xFFFFE0: LightYellow
|
||||
0xFFFFF0: Ivory
|
||||
0xFFFFFF: White
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||||
******************************
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||||
0xDA70D6: Orchid
|
||||
0xDAA520: GoldenRod
|
||||
0xDB7093: PaleVioletRed
|
||||
0xDC143C: Crimson
|
||||
0xDCDCDC: Gainsboro
|
||||
0xDDA0DD: Plum
|
||||
0xDEB887: BurlyWood
|
||||
0xE0FFFF: LightCyan
|
||||
0xE6E6FA: Lavender
|
||||
*/
|
||||
```
|
||||
|
||||
在 **main()** 方法中可以看到 **NavigableMap** 的各种功能。 因为 **NavigableMap** 具有键顺序，所以它使用了 **firstEntry()** 和 **lastEntry()** 的概念。调用 **headMap()** 会生成一个 **NavigableMap** ，其中包含了从 **Map** 的开头到 **headMap()** 参数中所指向的一组元素，其中 **boolean** 值指示结果中是否包含该参数。调用 **tailMap()** 执行了类似的操作，只不过是从参数开始到 **Map** 的末尾。 **subMap()** 则允许生成 **Map** 中间的一部分。
|
||||
|
||||
**ceilingEntry()** 从当前键值对向上搜索下一个键值对，**floorEntry()** 则是向下搜索。 **descendingMap()** 反转了 **NavigableMap** 的顺序。
|
||||
|
||||
如果需要通过分割 **Map** 来简化所正在解决的问题，则 **NavigableMap** 可以做到。具有类似的功能的其它集合实现也可以用来帮助解决问题。
|
||||
|
||||
<!-- Filling Collections -->
|
||||
## 集合的fill方法
|
||||
## 填充集合
|
||||
|
||||
|
||||
<!-- Custom Collection and Map using Flyweight -->
|
||||
|
||||
Reference in New Issue
Block a user