題目

題目也可抽象為統計檔案正文中某字串出現的次數.

解題思路

1.Java中關鍵字共有50個,分別為:

    final String[] KEYWORDS = { //50個關鍵字
            "abstract", "assert", "boolean", "break", "byte",
            "case", "catch", "char", "class", "const",
            "continue", "default", "do", "double", "else",
            "enum", "extends"
 
, "final", "finally", "float",
            "for", "goto", "if", "implements", "import",
            "instanceof", "int", "interface", "long", "native",
            "new", "package", " private", " protected", "public",
            "return", "strictfp", "short", "static", "super",
            "switch"
 
, "synchronized", "this", "throw", "throws",
            "transient", "try", "void", "volatile", "while"
    };

2.說明與初始化

	...
    ArrayList<File> fileList;//儲存Java檔案列表
    File root;//給定的目錄
    Map keywords; //HashMap用於儲存關鍵字與出現次數, 例如:<key,value>=<"int",3>
    ...
        public KeywordsAnalyzer
 
(String pathName) {
        root = new File(pathName);
        fileList = new ArrayList<>();
        keywords = new HashMap();
        for (String word : KEYWORDS) {
            keywords.put(word,0);//按KEYWORDS順序初始化Map
        }

    }

3.使用遞迴搜尋目錄下所有的Java檔案

    ArrayList<File> fileList; 
    File root; 
        public void searchFiles() {
        File[] files = root.listFiles();
        int length = files.length;
        for (int i = 0; i < length; i++) {
            if (files[i].isDirectory()) {
                root = files[i];
                searchFiles();
            } else {
                if (files[i].getName().endsWith(".java"))
                    fileList.add(files[i]);
            }
        }
    }

3.關鍵字篩查

讀取檔案中的某一行,將該行split為字串陣列,逐個判斷是否為關鍵字.
需要首先去除非字母和數字字元的影響,例如:

private void fixUp(int k) {
//直接分割會少計算了一個int
private
void 
fixUp(int //此處有一個關鍵字int
k) 
{
//使用正則表示式"\\W"處理成
private
void 
fixUp 
int
k

程式碼如下:

    public void matchKeywords(String line) {
        String[] wordList = line.replaceAll("\\W", " ").split(" ");
        for (int i = 0; i < wordList.length; i++) {
            for (int j = 0; j < 50; j++) {
                if (wordList[i].equals(KEYWORDS[j])) { //迴圈判斷
                    int count = (int) keywords.get(KEYWORDS[j]);
                    keywords.put(KEYWORDS[j], count + 1);
                }
            }
        }

    }

4.處理註釋

說明有四種不同的註釋,分別為:

   /**
    文件註釋
   */
   
   /*
     多行註釋
   */
  
   //單行註釋
   
   int number;  /*第一行當作程式碼
                           *
                   其他行當作註釋 */

讀取檔案中的每一行,首先判斷是否屬於註釋,若屬於則跳過,若不屬於則進行關鍵字篩查.

    public void countKeyWords(File file) throws IOException {
        BufferedReader input = new BufferedReader(new FileReader(file));
        String line = null;
        while ((line = input.readLine()) != null) {
            line = line.trim();
            if (line.startsWith("//")) continue; //不處理單行註釋
            else if (line.contains("/*")) { //多行,文件與尾行註釋
                if (!line.startsWith("/*")) matchKeywords(line);//第一行算程式碼,其餘算註釋
                while (!line.endsWith("*/")) {
                    line = input.readLine().trim();
                }
            }
            matchKeywords(line); //對程式碼行進行統計
        }
    }

流程與結果輸出

   public void keywordsAnalyze() {
        for (File file : fileList) {
            try {
                countKeyWords(file);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        //排序並輸出結果
        List<Map.Entry<String, Integer>> list = new ArrayList<Map.Entry<String, Integer>>(keywords.entrySet());
        Collections.sort(list, new Comparator<Map.Entry<String, Integer>>() {
            @Override
            public int compare(Map.Entry<String, Integer> o1, Map.Entry<String, Integer> o2) {
                return o2.getValue().compareTo(o1.getValue());
            }
        });
        int count = 0;
        for (Map.Entry<String, Integer> word : list) {
            count++;
            System.out.print(word.getKey() + ": " + word.getValue() + " ");
            if (count == 5) { //每行輸出5個關鍵字
                count = 0;
                System.out.println();
            }
        }

    }

這裡輸出的結果是按照出現次數的多少降序排序.這裡涉及了HashMap的按值排序的思路.詳情可以參考我的另外一篇文章 還沒寫好,文章裡面同樣以關鍵字為例,分析了HashMap按鍵排序和按值排序兩種簡便方法.

測試結果

對測試用例進行統計得到如下結果:

原始碼下載

包含完整程式碼與測試用例.

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