問題描述

想知道有沒有比如下計算給定字符串的字符數更簡單的方法?

Wondering is there more simple way than computing the character count of a given string as below?

String word = "AAABBB";
    Map<String, Integer> charCount = new HashMap();
    for(String charr: word.split("")){
        Integer added = charCount.putIfAbsent(charr, 1);
        if(added != null)
            charCount.computeIfPresent(charr,(k,v) -> v+1);
    }

    System.out.println(charCount);

推薦答案

計算字符串中每個字符出現次數的最簡單方法，完全支持 Unicode (Java 11+)¹:

Simplest way to count occurrence of each character in a string, with full Unicode support (Java 11+)¹:

String word = "AAABBB";
Map<String, Long> charCount = word.codePoints().mapToObj(Character::toString)
        .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));
System.out.println(charCount);

^{1) 完全支持 Unicode 的 Java 8 版本在答案的末尾.}

輸出

{A=3, B=3}

<小時>

更新:對于 Java 8+(不支持來自補充平面的字符，例如表情符號):

UPDATE: For Java 8+ (doesn't support characters from supplemental planes, e.g. emoji):

Map<String, Long> charCount = IntStream.range(0, word.length())
        .mapToObj(i -> word.substring(i, i + 1))
        .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));

<小時>

更新 2: 也適用于 Java 8+.

UPDATE 2: Also for Java 8+.

我錯了，以為 codePoints() 直到 Java 9 才添加.它是在 Java 8 中添加到 CharSequence 接口，因此 String 在 Java 8 中，并顯示為 在 Java 9 中添加 用于更高版本的 javadoc.

I was mistaken, thinking that codePoints() wasn't added until Java 9. It was added in Java 8 to the CharSequence interface, so it doesn't show in javadoc for String in Java 8, and shows as added in Java 9 for later versions of the javadoc.

但是，Character.toString (int codePoint) 方法直到 Java 11 才被添加，所以要使用 Character.toString (char c) 方法，我們可以使用 chars() 在 Java 8 中:

However, the Character.toString?(int codePoint) method wasn't added until Java 11, so to use the Character.toString?(char c) method, we can use chars() in Java 8:

Map<String, Long> charCount = word.chars().mapToObj(c -> Character.toString((char) c))
        .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));

或者對于完整的 Unicode 支持，包括.補充平面，我們可以使用 codePoints() 和 String(int[] codePoints, int offset, int count) 構造函數，在 Java 8 中:

Or for full Unicode support, incl. supplemental planes, we can use codePoints() and the String(int[] codePoints, int offset, int count) constructor, in Java 8:

Map<String, Long> charCount = word.codePoints()
        .mapToObj(cp -> new String(new int[] { cp }, 0, 1))
        .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));

這篇關于Java8:使用字符串的字符數創建 HashMap的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！