关于Map常用的方法

1 将Map转换成List

// key list
List keyList = new ArrayList(map.keySet());
// value list
List valueList = new ArrayList(map.valueSet());
// key-value list
List entryList = new ArrayList(map.entrySet());

2 遍历Map

for(Entry entry: map.entrySet()) {
  // get key
  K key = entry.getKey();
  // get value
  V value = entry.getValue();
}

Iterator itr = map.entrySet().iterator();
while(itr.hasNext()) {
  Entry entry = itr.next();
  // get key
  K key = entry.getKey();
  // get value
  V value = entry.getValue();
}

3 对Map的key进行排序

List list = new ArrayList(map.entrySet());
Collections.sort(list, new Comparator() {

  @Override
  public int compare(Entry e1, Entry e2) {
    return e1.getKey().compareTo(e2.getKey());
  }

});

SortedMap sortedMap = new TreeMap(new Comparator() {

  @Override
  public int compare(K k1, K k2) {
    return k1.compareTo(k2);
  }

});
sortedMap.putAll(map);

4 对Map的value进行排序

List list = new ArrayList(map.entrySet());
Collections.sort(list, new Comparator() {

  @Override
  public int compare(Entry e1, Entry e2) {
    return e1.getValue().compareTo(e2.getValue());
  }

});

5 创建一个空的Map对象

map = Collections.emptyMap();

map = new HashMap();