如何迭代 TreeMap？

Question

可能的重复：
如何迭代映射中的每个条目？< /a>

我想迭代 TreeMap，对于具有特定值的所有键，我希望将它们添加到新的 TreeMap 中。我该怎么做？

Answer 1

假设类型 TreeMap:(

for(Map.Entry<String,Integer> entry : treeMap.entrySet()) {
  String key = entry.getKey();
  Integer value = entry.getValue();

  System.out.println(key + " => " + value);
}

键和值类型当然可以是任何类)

Answer 2

    //create TreeMap instance
    TreeMap treeMap = new TreeMap();

    //add key value pairs to TreeMap
    treeMap.put("1","One");
    treeMap.put("2","Two");
    treeMap.put("3","Three");

    /*
      get Collection of values contained in TreeMap using
      Collection values()        
    */
    Collection c = treeMap.values();

    //obtain an Iterator for Collection
    Iterator itr = c.iterator();

    //iterate through TreeMap values iterator
    while(itr.hasNext())
      System.out.println(itr.next());

或：

   for (Map.Entry<K,V> entry : treeMap.entrySet()) {
        V value = entry.getValue();
        K key = entry.getKey();
   }

或：

   // Use iterator to display the keys and associated values
   System.out.println("Map Values Before: ");
   Set keys = map.keySet();
   for (Iterator i = keys.iterator(); i.hasNext();) {
     Integer key = (Integer) i.next();
     String value = (String) map.get(key);
     System.out.println(key + " = " + value);
   }

Answer 3

只是指出迭代任何映射的通用方法：

 private <K, V> void iterateOverMap(Map<K, V> map) {
    for (Map.Entry<K, V> entry : map.entrySet()) {
        System.out.println("key ->" + entry.getKey() + ", value->" + entry.getValue());
    }
    }

Answer 4

使用 Google 收藏集，假设 K 是您的密钥类型：

Maps.filterKeys(treeMap, new Predicate<K>() {
  @Override
  public boolean apply(K key) {
    return false; //return true here if you need the entry to be in your new map
  }});

您可以使用 如果您也需要该值，请改为使用filterEntries。