java - 如何计算ArrayList中某个单词出现的次数？

Question

这个问题已经有答案了:

How to count the number of occurrences of an element in a List (25 个回答)

已关闭 6 年前。

我编写了以下代码并得到了输出。导入java.util.ArrayList;

public class DuplicatesinArrayList {

    public static void main(String[] args) {

        ArrayList <String> al = new ArrayList<>();
        al.add("Soumen");
        al.add("Rahul");
        al.add("Soumen");
        al.add("Ram");
        al.add("Rahul");
        al.add("Rahul");
        al.add("Rahul");
        al.add("Ram");
        al.add("Ram");
        al.add("Ram");
        al.add("Ram");

        for (int i = 0; i < al.size(); i++) {  
            int ctr = 0;
            for (int j = 0; j < al.size(); j++) {
                if(al.get(i).equals(al.get(j)))
                    ctr++;
            }
            System.out.println(al.get(i)+" present " + ctr + " times"); 
        }
    }
}

结果如下:

Soumen present 2 times
Rahul present 4 times
Soumen present 2 times
Ram present 5 times
Rahul present 4 times
Rahul present 4 times
Rahul present 4 times
Ram present 5 times
Ram present 5 times
Ram present 5 times
Ram present 5 times

我希望每个单词都有一个结果。有人可以帮忙吗？

Answer 1

您可以使用 map

Map<String, Integer> map = new HashMap<>();
for (String s : al) {
    if (map.containsKey(s)) map.put(s, map.get(s) + 1);
    else map.put(s, 1);
}

for (Map.Entry<String, Integer> entry : map.entrySet()) {
    System.out.println(entry.getKey()+" present " + entry.getValue() + " times");
}

或者您可以使用 java8 流:

al.stream().collect(groupingBy(o -> o, counting())).forEach((name, count) -> System.out.println(name + " present " + count + " times"));