commons的迭代器和双向Map——高淇JAVA300讲笔记之commons

案例一：迭代器

  1 package com.bjsxt.others.commons;
  2 
  3 import java.util.ArrayList;
  4 import java.util.Iterator;
  5 import java.util.List;
  6 
  7 import org.apache.commons.collections4.IterableMap;
  8 import org.apache.commons.collections4.MapIterator;
  9 import org.apache.commons.collections4.Predicate;
 10 import org.apache.commons.collections4.iterators.ArrayListIterator;
 11 import org.apache.commons.collections4.iterators.FilterIterator;
 12 import org.apache.commons.collections4.iterators.LoopingIterator;
 13 import org.apache.commons.collections4.iterators.UniqueFilterIterator;
 14 import org.apache.commons.collections4.map.HashedMap;
 15 
 16 
 17 /**
 18  * 迭代器的扩展
 19  * 1、MapIterator 以后不再使用map.keySet.iterator访问
 20  *   IterableMap  HashedMap
 21  * 2、UniqueFilterIterator 去重迭代器
 22  * 3、FilterIterator 自定义过滤 + Predicate
 23  * 4、LoopingIterator 循环迭代器
 24  * 5、ArrayListIterator 数组迭代器
 25  *
 26  */
 27 public class Demo06 {
 28 
 29     public static void main(String[] args) {
 30 //        mapIt();
 31 //        uniqueIt();
 32 //        filterIt();
 33 //        loopIt();
 34         arrayIt();
 35     }
 36     /**
 37      * 数组迭代器
 38      */
 39     public static void arrayIt() {
 40         System.out.println("=======数组迭代器======");
 41         int[] arr = {1,2,3,4,5};
 42         //数组迭代器
 43 //        Iterator<Integer> it = new ArrayListIterator<Integer>(arr);
 44         //指定起始索引和结束索引
 45         Iterator<Integer> it = new ArrayListIterator<Integer>(arr,1,3);
 46         while(it.hasNext()) {
 47             System.out.println(it.next());
 48         }
 49     }
 50     
 51     /**
 52      * 循环迭代器
 53      */
 54     public static void loopIt() {
 55         System.out.println("=======循环迭代器======");
 56         List<String> list = new ArrayList<String>();
 57         list.add("refer");
 58         list.add("dad");
 59         list.add("bjsxt");
 60         list.add("moom");
 61         
 62         Iterator<String> it = new LoopingIterator(list);
 63         for(int i=0;i<5;i++) {
 64             System.out.println(it.next());
 65         }
 66         
 67     }
 68     
 69     
 70     /**
 71      * 自定义迭代器
 72      */
 73     public static void filterIt() {
 74         System.out.println("=======自定义迭代器======");
 75         List<String> list = new ArrayList<String>();
 76         list.add("refer");
 77         list.add("dad");
 78         list.add("bjsxt");
 79         list.add("moom");
 80         //自定义条件判断
 81         Predicate<String> pre = new Predicate<String>() {
 82             @Override
 83             public boolean evaluate(String value) {
 84                 //回文判断
 85                 return new StringBuilder(value).reverse().toString().equals(value);
 86             }
 87         };
 88         
 89         //过滤器
 90         Iterator<String> it = new FilterIterator(list.iterator(),pre);
 91         while(it.hasNext()) {
 92             System.out.println(it.next());
 93         }
 94     }
 95     
 96     /**
 97      * 去重迭代器
 98      */
 99     public static void uniqueIt() {
100         System.out.println("=======去重迭代器======");
101         List<String> list = new ArrayList<String>();
102         list.add("a");
103         list.add("b");
104         list.add("a");
105         //去除重复的过滤器
106         Iterator<String> it = new UniqueFilterIterator(list.iterator());
107         while(it.hasNext()) {
108             System.out.println(it.next());
109         }
110     }
111     
112     /**
113      * map迭代器
114      */
115     public static void mapIt() {
116         System.out.println("=======map迭代器======");
117         IterableMap<String,String> map = new HashedMap<String,String>();
118         map.put("a","bjsxt");
119         map.put("b","sxt");
120         map.put("c","good");
121         //使用MapIterator
122         MapIterator<String,String> it = map.mapIterator();
123         while(it.hasNext()) {
124             //一定要it.next()
125             String key = it.next();
126             String value = it.getValue();
127             System.out.println(key+"-->"+value);
128                 
129         }
130             
131     }
132 
133 }

案例二：有序和无序的双向Map

 1 package com.bjsxt.others.commons;
 2 
 3 import org.apache.commons.collections4.BidiMap;
 4 import org.apache.commons.collections4.MapIterator;
 5 import org.apache.commons.collections4.bidimap.DualHashBidiMap;
 6 import org.apache.commons.collections4.bidimap.DualTreeBidiMap;
 7 
 8 /**
 9  * 双向Map 要求键与值都不能重复
10  * BidiMap  inverseBidiMap()
11  * 1、DualTreeBidMap: 有序
12  * 2、DualHashBidMap: 无序
13  *
14  */
15 public class Demo07 {
16 
17     public static void main(String[] args) {
18         hashMap();
19         treeMap();
20     }
21     
22     /**
23      * 有序的双向Map
24      */
25     public static void treeMap() {
26         System.out.println("=======有序的双向Map=======");
27         BidiMap<String,String> map = new DualTreeBidiMap<String,String>();
28         map.put("bj", "bj@test.com");
29         map.put("sxt", "sxt@qq.com");
30     
31         //遍历查看
32         MapIterator<String,String> it = map.inverseBidiMap().mapIterator();
33         while(it.hasNext()) {
34             String key = it.next();
35             String value = it.getValue();
36             System.out.println(key+"-->"+value);
37         }
38     }
39     
40     /**
41      * 无序的双向Map
42      */
43     public static void hashMap() {
44         System.out.println("=======无序的双向Map=======");
45         BidiMap<String,String> map = new DualHashBidiMap<String,String>();
46         map.put("bj", "bj@test.com");
47         map.put("sxt", "sxt@qq.com");
48         //反转
49         System.out.println(map.inverseBidiMap().get("sxt@qq.com"));
50         //遍历查看
51         MapIterator<String,String> it = map.inverseBidiMap().mapIterator();
52         while(it.hasNext()) {
53             String key = it.next();
54             String value = it.getValue();
55             System.out.println(key+"-->"+value);
56         }
57     }
58 
59 }

运行结果：

=======无序的双向Map=======
sxt
bj@test.com-->bj
sxt@qq.com-->sxt
=======有序的双向Map=======
bj@test.com-->bj
sxt@qq.com-->sxt

案例三：Bag 包

 1 package com.bjsxt.others.commons;
 2 
 3 import java.util.Iterator;
 4 import java.util.Set;
 5 
 6 import org.apache.commons.collections4.Bag;
 7 import org.apache.commons.collections4.bag.HashBag;
 8 import org.apache.commons.collections4.bag.TreeBag;
 9 
10 /**
11  * Bag 包 允许重复
12  * 1、HashBag 无序
13  * 2、TreeBag 无序
14  * 统计单词的出现次数
15  *
16  */
17 public class Demo08 {
18     public static void main(String[] args) {
19         hashBag();
20         treeBag();
21         String str = "this is a cat and that is a mice where is the food";
22         //分割字符串
23         String[] strArray = str.split(" ");
24         Bag<String> bag = new TreeBag<String>();
25         for(String temp:strArray) {
26             bag.add(temp);
27         }
28         
29         System.out.println("========统计次数======");
30         Set<String> keys = bag.uniqueSet();
31         for(String letter:keys) {
32             System.out.println(letter+"-->"+bag.getCount(letter));
33         }
34         
35     }
36     /**
37      * 有序
38      */
39     public static void treeBag() {
40         System.out.println("======有序的包=======");
41         Bag<String> bag = new TreeBag<String>();
42         bag.add("a");
43         bag.add("a",5);
44         bag.remove("a",2);
45         bag.add("b");
46         bag.add("c");
47         
48         Iterator<String> it = bag.iterator();
49         while(it.hasNext()) {
50             System.out.println(it.next());
51         }
52     }
53     /**
54      * 无序
55      */
56     public static void hashBag() {
57         System.out.println("======无序的包=======");
58         Bag<String> bag = new HashBag<String>();
59         bag.add("a");
60         bag.add("a",5);
61         bag.remove("a",2);
62         bag.add("b");
63         bag.add("c");
64         
65         Iterator<String> it = bag.iterator();
66         while(it.hasNext()) {
67             System.out.println(it.next());
68         }
69     }
70 }

运行结果：

======无序的包=======
a
a
a
a
b
c
======有序的包=======
a
a
a
a
b
c
========统计次数======
a-->2
and-->1
cat-->1
food-->1
is-->3
mice-->1
that-->1
the-->1
this-->1
where-->1

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原文地址：https://www.cnblogs.com/swimminglover/p/8402180.html