HashMap遍历、排序

HashMap<String, Integer> map = new HashMap<String, Integer>();

// 向集合中添加元素
map.put("z", 1);
map.put("fh", 2);
map.put("fd", 3);
map.put("b", 4);

//获取map集合的所有value的Collection集合（于集合中无序存放）
Collection<Integer> collection = map.values();
System.out.println("==获取map集合的所有key的Collection集合:==");
System.out.println(map.keySet()); // [fh, b, z, fd]
System.out.println("==获取map集合的所有value的Collection集合:==");
System.out.println(collection); // [2, 4, 1, 3]


==获取map集合的所有key的Collection集合:==
[fh, b, z, fd]
==获取map集合的所有value的Collection集合:==
[2, 4, 1, 3]

System.out.println("==遍历==");

// 遍历第一种方法——返回所有key的集合
Set<String> strings = map.keySet();

// 1. 使用迭代器
Iterator<String> iterator = strings.iterator();
while (iterator.hasNext()){
       String key = iterator.next();
       Integer value = map.get(key);
       System.out.println(key + "===" + value);
}

System.out.println("-----");

// 2. 使用for
for (String s : strings){
       System.out.println(s + "===" + map.get(s));
}

System.out.println("==遍历==");

// 遍历第二种方法
Set<Map.Entry<String, Integer>> entries = map.entrySet();

// 1. 使用迭代器
Iterator<Map.Entry<String, Integer>> iterator1 = entries.iterator();
while (iterator1.hasNext()) {
      Map.Entry<String, Integer> next = iterator1.next();
      System.out.println(next.getKey() + "===" + next.getValue());
}

System.out.println("-----");

// 2. 使用for
for (Map.Entry<String, Integer> str: entries) {
       System.out.println(str.getKey() + "===" + str.getValue());
}


==遍历==
fh===2
b===4
z===1
fd===3
-----
fh===2
b===4
z===1
fd===3
==遍历==
fh===2
b===4
z===1
fd===3
-----
fh===2
b===4
z===1
fd===3

System.out.println("==根据value排序==");

//根据value升序排序
System.out.println("--升序--");
ArrayList<Map.Entry<String, Integer>> list1 = new ArrayList<Map.Entry<String, Integer>>(map.entrySet());

Collections.sort(list1, new Comparator<Map.Entry<String, Integer>>() {
     public int compare(Map.Entry<String, Integer> o1, Map.Entry<String, Integer> o2) {
           return o1.getValue().compareTo(o2.getValue());
     }
});

for (int i = 0;i < list1.size();i++){
     String key = list1.get(i).getKey();
     Integer value = list1.get(i).getValue();
     System.out.println(key + "===" + value);
}

System.out.println("--降序--");
ArrayList<Map.Entry<String, Integer>> list2 = new ArrayList<Map.Entry<String, Integer>>(map.entrySet());

Collections.sort(list2, new Comparator<Map.Entry<String, Integer>>() {
      public int compare(Map.Entry<String, Integer> o1, Map.Entry<String, Integer> o2) {
           return o2.getValue().compareTo(o1.getValue());
      }
});

for (int i = 0;i < list2.size();i++){
      String key = list2.get(i).getKey();
      Integer value = list2.get(i).getValue();
      System.out.println(key + "===" + value);
}

System.out.println("==根据key排序==");
System.out.println("--升序--");
ArrayList<Map.Entry<String, Integer>> list3 = new ArrayList<Map.Entry<String, Integer>>(map.entrySet());

Collections.sort(list3, new Comparator<Map.Entry<String, Integer>>() {
      public int compare(Map.Entry<String, Integer> o1, Map.Entry<String, Integer> o2) {
           return o1.getKey().compareTo(o2.getKey());
      }
});

for (int i = 0;i < list3.size();i++){
      String key = list3.get(i).getKey();
      Integer value = list3.get(i).getValue();
      System.out.println(key + "===" + value);
}

System.out.println("--降序--");
ArrayList<Map.Entry<String, Integer>> list4 = new ArrayList<Map.Entry<String, Integer>>(map.entrySet());

Collections.sort(list4, new Comparator<Map.Entry<String, Integer>>() {
      public int compare(Map.Entry<String, Integer> o1, Map.Entry<String, Integer> o2) {
           return o2.getKey().compareTo(o1.getKey());
      }
});

for (int i = 0;i < list4.size();i++){
      String key = list4.get(i).getKey();
      Integer value = list4.get(i).getValue();
      System.out.println(key + "===" + value);
}


==根据value排序==
--升序--
z===1
fh===2
fd===3
b===4
--降序--
b===4
fd===3
fh===2
z===1
==根据key排序==
--升序--
b===4
fd===3
fh===2
z===1
--降序--
z===1
fh===2
fd===3
b===4