使用 Java 8 获取集合中所有项目的最常用名称的正确方法

Question

I am currently trying to find the best way to find the most common name from all items in a Set.

The object in a Set are Person objects:

public class Person {
     private String name;

     ...

     public String getName() {
          return name;
     }
}

In the method findMostCommonName, I want to find the most common name of all the Person objects in the given set. Is there a Java 8 way to do that?

public String findMostCommonName(Set<Person> personSet) {

//Code here

}

Thanks.

Answer 1

You can use

public String findMostCommonName(Set<Person> personSet) {
    return personSet.stream().map(Person::getName)
        .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()))
        .entrySet().stream()
        .max(Map.Entry.comparingByValue()).map(Map.Entry::getKey)
        .orElse(null);
}

personSet.stream().map(Person::getName) straight-forwardly creates a stream of name strings, .collect(Collectors.groupingBy(Function.identity(), Collectors.counting())) counts the number of occurences into a Map<String,Long> , then .entrySet().stream() will stream over the entries and .max(Map.Entry.comparingByValue()).map(Map.Entry::getKey) will find the entry with the highest value, ie count, and extract the key, which is the string with that count.

The last .orElse(null) determines how to handle the situation when there is no result, ie personSet is empty. If you use get() instead, a NoSuchElementException will be thrown in that case.

In case of a tie, an arbitrary name out of the names with the highest number of occurrences will be returned.

Answer 2

您可以使用嵌套循环并使用equals方法遍历集合以比较名称，如果它返回true，则将+1添加到计数器中并保持名称多次出现，或者可以使用键/值对象（例如HashMap和存储每个名称出现的次数

Answer 3

public String findMostCommonName(Set<Person> personSet) {
    return personSet.stream().parallel().map(Person::getName)
        .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()))
        .entrySet().stream().parallel()
        .max(Map.Entry.comparingByValue()).map(Map.Entry::getKey)
        .orElse(null);
}

Just added Parallelism to speed up the code by around 1.2x