获取Key及其值

e.g

private Map<String, Integer> team1 = new HashMap<String, Integer>();
  team1.put("United", 5);
  team1.put("Barcelona", 6);
    for (String key:team1.keySet()){
                     System.out.println("Key:" + key +" Value:" + team1.get(key)+" Count:"+Collections.frequency(team1, key));// Get Key and value and count
                }

将打印:键:联合值:5 值:6

public class MyHashMapKeys {

    public static void main(String a[]){
        HashMap<String, String> hm = new HashMap<String, String>();
        //add key-value pair to hashmap
        hm.put("first", "FIRST INSERTED");
        hm.put("second", "SECOND INSERTED");
        hm.put("third","THIRD INSERTED");
        System.out.println(hm);
        Set<String> keys = hm.keySet();
        for(String key: keys){
            System.out.println(key);
        }
    }
}

一个解决方案是，如果你知道键的位置，将键转换为一个String数组，并返回该位置的值:

public String getKey(int pos, Map map) {
    String[] keys = (String[]) map.keySet().toArray(new String[0]);

    return keys[pos];
}

如果你只是需要一些简单的验证。

public String getKey(String key)
{
    if(map.containsKey(key)
    {
        return key;
    }
    return null;
}

然后你可以搜索任何键。

System.out.println( "Does this key exist? : " + getKey("United") );

一个HashMap包含多个键。您可以使用keySet()来获取所有键的集合。

team1.put("foo", 1);
team1.put("bar", 2);

将存储1，键“foo”和2，键“bar”。遍历所有键:

for ( String key : team1.keySet() ) {
    System.out.println( key );
}

将打印“foo”和“bar”。

Foreach也可以使用。

team1.forEach((key, value) -> System.out.println(key));