Java Hashmap 实现

Question

我想使用 HashMap 来计算文件中多个字符串出现的次数。我该怎么做呢？另外，我是否能够以类似的方式计算唯一字符串的数量？示例将非常感激。

Answer 1

作为示例，下面的程序将从文件中读取单词并计算遇到 Java 关键字的次数。

import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.util.Map;
import java.util.HashMap;

public class CountKeywords {

    public static void main(String args[]) {

        String[] theKeywords = { "abstract", "assert", "boolean", "break", "byte", "case", "catch", "char", "class", "const", "continue", "default", "do", "double", "else", "enum", "extends", "false", "final", "finally", "float", "for", "goto", "if", "implements", "import", "instanceof", "int", "interface", "long", "native", "new", "null", "package", "private", "protected", "public", "return", "short", "static", "strictfp", "super", "switch", "synchronized", "this", "throw", "throws", "transient", "true", "try", "void", "volatile", "while" };

        // put each keyword in the map with value 0 
        Map<String, Integer> theKeywordCount = new HashMap<String, Integer>();
        for (String str : theKeywords) {
            theKeywordCount.put(str, 0);
        }

        FileReader fr;
        BufferedReader br;
        File file = new File(args[0]); // the filename is passed in as a String

        // attempt to open and read file
        try {
            fr = new FileReader(file);
            br = new BufferedReader(fr);

            String sLine;

            // read lines until reaching the end of the file
            while ((sLine = br.readLine()) != null) {

                // if an empty line was read
                if (sLine.length() != 0) {

                    // extract the words from the current line in the file
                    if (theKeywordCount.containsKey(sLine)) {
                        theKeywordCount.put(sLine, theKeywordCount.get(sLine) + 1);
                    }
                }
            }

        } catch (FileNotFoundException exception) {
            // Unable to find file.
            exception.printStackTrace();
        } catch (IOException exception) {
            // Unable to read line.
            exception.printStackTrace();
        } finally {
                br.close();
            }

        // count how many times each keyword was encontered
        int occurrences = 0;
        for (Integer i : theKeywordCount.values()) {
            occurrences += i;
        }

        System.out.println("\n\nTotal occurences in file: " + occurrences);
    }
}

要回答有关唯一字符串的问题，您可以以类似的方式调整我使用 HashMap 的方式。

1. 创建一个新的 HashMap，将其命名为 uniqueStrings
2. 从文件中读取字符串时，检查记录计数的 HashMap 是否包含当前字符串
   • 如果没有，则将其添加到 uniqueStrings
   • 如果存在，则将其从 uniqueStrings 中删除
3. 读取完文件后，uniqueStrings 中将只有唯一的字符串

如果您有疑问，请告诉我。

希望这会有所帮助。
赫里斯托