计算有多少HashMap条目具有给定值

Question

public final static HashMap<String, Integer> party = new HashMap<String, Integer>();
party.put("Jan",1);
party.put("John",1);
party.put("Brian",1);
party.put("Dave",1);
party.put("David",2);

如何返回多少人的价值1

Answer 1

我只是对HashMap值使用Collections.frequency()方法,就像这样.

int count = Collections.frequency(party.values(), 1);
System.out.println(count);
===> 4

或者一般解决方案,生成频率与数字的映射.

Map<Integer, Integer> counts = new HashMap<Integer, Integer>();
for (Integer c : party.values()) {
    int value = counts.get(c) == null ? 0 : counts.get(c);
    counts.put(c, value + 1);
}
System.out.println(counts);
==> {1=4, 2=1}

Answer 2

使用 Java 8：

party.values().stream().filter(v -> v == 1).count();

Answer 3

尝试这个：

int counter = 0;
Iterator it = party.entrySet().iterator();
while (it.hasNext()) {
  Map.Entry pairs = (Map.Entry)it.next();
  if(pairs.getValue() == 1){
    counter++; 
  }      
}
System.out.println("number of 1's: "+counter);