题目：

来自于xd Java大作业，花了我老长时间：

实现一个类 KeywordIdentifier，其中的核心方法的功能是读入一个 java 程序源文件，在控制台输出各个关键字的个数。

1. 关于源文件读取的方法，请先自学教材中流试 I/O 相关的内容（7.1 节），建议逐行读取源文件内容进行分析。
2. 关于关键字个数的统计，请先自学 Map 集合类的使用方法（5.6.6 节）。
3. 对 Java 语言的所有关键字进行统计，不是仅针对部分关键字。
4. 要求具备“跳过注释”功能，注释中出现的关键字不计入关键字个 数（要求支持单行注释“//…”和多行注释“/**/”的跳过，可不考虑 注释嵌套的情况）。

分析

• 利用RandomAccessFile读取文件（方便按行读取
• 统计关键字借助于Map类，一般用HashMap就行
• 重点就是处理注释，解决方案就是按行读取到的字符串先进行删注释的操作
• 单行注释直接利用String的replaceAll（正则表达式匹配目标，替换为空""）
• 多行注释是借助于一个变量记录读取的内容是否在注释内，即是否被/**/包裹

处理每一行的字符也是重点（这里借鉴了别人的解决方案

//利用正则先把乱七八糟的符号全部干掉
String unsigned_str = s.replaceAll("\\W", " ");
//把多个空格替换为单个
String str = unsigned_str.replaceAll(" +", " ");
//这样就直接以空格为界，可以得到由每个单词组成的字符数组
String[] str_word = str.split(" ");

代码：

立志写出最优雅的代码

import java.io.* ;
import java.util.HashMap;
import java.util.Map;

public class KeywordIdentifier {

    static Map<String, Integer> keyWordCount = new HashMap<>();

    public static void getKeyWord(){

        String[] keywords ={"abstract","assert","boolean","break","byte","case","catch","char","class","const",
                "continue","default","do","double","else","enum","extends","final","finally","float","for",
                "if","implements","import","instanceof","int","interface","long","native","new","package",
                "private","protected","public","return","short","static","strictfp","super","switch","synchronized",
                "this","throw","throws","transient","try","void","volatile","while"};
        for (String keyword : keywords) {
            keyWordCount.put(keyword,0);
        }
    }

    static boolean comment=false;
    public static void keyWordCounter(String s){
        if (s.contains("//")) {
           s=s.replaceAll("//.+","");
        }
        if (s.contains("/*")){
            comment=true;
        }
        if (comment) {
            s=clearCommons(s);
        }
        if (s.contains("*/")) {
            comment=false;
        }

        String unsigned_str = s.replaceAll("\\W", " ");
        String str = unsigned_str.replaceAll(" +", " ");
        String[] str_word = str.split(" ");
        
        for(String word : str_word) {
            if(keyWordCount.containsKey(word)) {
                keyWordCount.put(word, keyWordCount.get(word)+1);
            }
        }

    }

    public static String clearCommons(String content) {
        StringBuilder str=new StringBuilder(content);
        if (content.contains("/*")&&content.contains("*/")) {
            str.replace(content.indexOf("/*"),content.indexOf("*/"),"");
        }else if (content.contains("/*")) {
            int start = content.indexOf("/*");
            str.replace(start,content.length(),"");
        }else if (content.contains("*/")) {
            int end = content.indexOf("*/");
            str.replace(0,end,"");
        } else {
            str.replace(0,str.length(),"");
        }
        content=str.toString();
        return content;
    }



    public static void main(String[] args) throws IOException {
        getKeyWord();
        long filePoint = 0;
        String line;
        RandomAccessFile file = new RandomAccessFile("src/Test.java", "r");
        long fileLength = file.length();
        while(filePoint < fileLength) {
            line = file.readLine();
            keyWordCounter(line);
            filePoint = file.getFilePointer();
        }

        file.close();
        keyWordCount.forEach((k,v)  -> {
            if (v>0)
            System.out.println(k+":"+v);
        });
    }
}

测试文件

尽可能的考虑了所有刁钻的情况

public class Test {
    public static void main(String[] args) {

    }//return
    //return
     static  /*static
    this return
     return */class test2 {
     }
     /*same return*/class test3{
     }
}

总结

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