集合框架

 1 package com.wang.map;
 2 
 3 import java.util.HashMap;
 4 import java.util.Iterator;
 5 import java.util.Map.Entry;
 6 import java.util.Set;
 7 
 8 public class TestHashMap {
 9 
10     /**
11      * @param args
12      */
13     public static void main(String[] args) {
14         //先将字符串放到一个char数组中去
15         String str = "ababcd";
16         char[] ch = str.toCharArray();
17         HashMap<Character, Integer> map = new HashMap<>();
18 
19         int count = 0;
20         //遍历数组，判断char数组中的元素重复情况
21         for (int i = 0; i < ch.length; i++) {
22             Integer value = map.get(ch[i]);
23             // 判断map中是否存在某值
24             if (value != null) {
25                 // 存在的话，返回value，将value+1后赋值给该key的值
26                 count = value;
27             }
28             count++;
29             // 不存在的话，将该值put进map，并且赋值1，
30             map.put(ch[i], count);
31             count = 0;
32         }
33         //System.out.println(map);
34          
35         //hashMap的entrySet()方法，将map中的数据存在set集合中，从而便于使用iteration遍历
36         Set<Entry<Character,Integer>> set = map.entrySet();
37         Iterator<Entry<Character, Integer>> it = set.iterator();
38         while (it.hasNext()) {
39             Entry<Character, Integer> next = it.next();
40             Character k = next.getKey();
41             Integer v = next.getValue();
42             System.out.println(k + "(" + v + ")");
43         }
44     }
45 
46 }

 1 package set;
 2 
 3 import java.util.HashSet;
 4 import java.util.Set;
 5 
 6 
 7 class Student{
 8     private int sn;
 9     private String name;
10     private int age;
11     public Student(int sn, String name, int age) {
12         super();
13         this.sn = sn;
14         this.name = name;
15         this.age = age;
16     }
17     public String toString() {
18         return "Student [sn=" + sn + ", name=" + name + ", age=" + age + "]";
19     }
20     public int hashCode() {
21         final int prime = 31;
22         int result = 1;
23         result = prime * result + sn;
24         return result;
25     }
26     public boolean equals(Object obj) {
27         if (this == obj)
28             return true;
29         if (obj == null)
30             return false;
31         if (getClass() != obj.getClass())
32             return false;
33         Student other = (Student) obj;
34         if (sn != other.sn)
35             return false;
36         return true;
37     }
38     
39     
40 }
41 public class HashSetDemo {
42 
43     /**
44      * @param args
45      */
46     public static void main(String[] args) {
47         Set<Student> stu = new HashSet<>();
48         stu.add(new Student(1,"zhangsan",17));
49         stu.add(new Student(1,"zhangsan",17));
50         stu.add(new Student(3,"lisi",18));
51         stu.add(new Student(4,"lisi",18));
52         System.out.println(stu.size());
53         System.out.println(stu.toString());
54     }
55 
56 }