如何使用 Java Comparator 使用两个参数对 ArrayList 进行排序？答案

【问题标题】：How to use Java Comparator to sort an ArrayList using two parameters?如何使用 Java Comparator 使用两个参数对 ArrayList 进行排序？
【发布时间】：2018-11-26 18:51:16
【问题描述】：

我使用 Java Comparator 按词频属性的降序对 Word 对象的 ArrayList 进行排序。 Word 对象的创建首先使用 hashmap 从 .txt 文件中读取单词，然后将 hashmap 转换为 Word 对象的 ArrayList。然后我想按字母顺序对频率相同的单词进行排序。

   while (reader.hasNext()) {
            word = reader.next().toLowerCase();
            word = word.substring(0, 1).toUpperCase() + word.substring(1);
            word = word.replaceAll("[^a-zA-Z ]", "");
            if (!word.contains("0") || !word.contains("1") || !word.contains("2") || !word.contains("3") || !word.contains("4") || !word.contains("5") || !word.contains("6") || !word.contains("7") || !word.contains("8") || !word.contains("9") || !word.contains("-") || !word.contains("_")) {
                // This is equivalent to searching every word in the list via hashing (O(1))
                if(!frequencyMap.containsKey(word)) {
                     frequencyMap.put(word, 1);
                } else {
                        // We have already seen the word, increase frequency.
                        frequencyMap.put(word, frequencyMap.get(word) + 1);
                }
            }
            counter++;
        }

 for(Map.Entry<String, Integer> entry : frequencyMap.entrySet()) {
    Word word = new Word(entry.getKey());
    word.frequency = entry.getValue();
    wordList.add(word);
 }
 Collections.sort(wordList, Word.WordFrequency);

public class Word {

    String value;
    int frequency;

    public Word(String v) {
        value = v;
        frequency = 1;
    }

    public String getValue() {
        return value;
    }

    public int getFrequency() {
        return frequency;
    }

    public static Comparator<Word> WordFrequency = new Comparator<Word>() {
        public int compare(Word w1, Word w2) {
            int w1Frequency = w1.getFrequency();
            int w2Frequency = w2.getFrequency();
            return w2Frequency-w1Frequency;
        }
    };
}

【问题讨论】：

if (w2Frequency - w1Frequency == 0) { return /* compareTheStrings*/; }
Java stream sort 2 variables ascending/desending的可能重复
@luk2302 感谢您的帮助，如果您想在此处发布答案，这就是我所使用的：if (w1Frequency == w2Frequency) { return w1.getValue().compareTo(w2.getValue()); } else { return w2Frequency-w1Frequency; }

标签： java arraylist comparator

【解决方案1】：

请参阅thenComparing 方法，该方法允许您在存在平局时提供比较键：

// sort using 'd' will sort 1st alphabetically, then by length
// (this is a totally arbitrary example)
Comparator<String> c = String::compareTo;
Comparator<String> d = c.thenComparing(s -> s.length());

【讨论】：