面试：小内存读取大文件实战

小内存读取大文件实战

内存只有1M但是读取1G的文件并对出现字符的频率排序top5

1. 获取文件
2. 定义每次读取文件的大小
3. 通过BufferedReader获取根据每次读取1m文件
4. 每次读取一行，并放到hashMap中
5. 遍历map并排序

public class topCharactorCounter {
    public static void main(String[] args) {
        File file = new File("E:\\1.txt");
        int  memoryLimit=1024*1024;
        int bufferSize=1024;
        Map<Character,Integer> chmap=new HashMap<>();
        try {
            FileReader fileReader = new FileReader(file);
            BufferedReader bufferedReader=new BufferedReader(fileReader);
            String line;
            while ((line=bufferedReader.readLine())!=null){
                if (!line.trim().isEmpty()){
                    for (char c:line.toCharArray()){
                        chmap.put(c,chmap.getOrDefault(c,0)+1);
                    }
                }  
            }
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
       int topCount=5;
        for (int i = 0; i < topCount; i++) {
            char topChar=' ';
            int max=0;
            for (Map.Entry<Character,Integer> entry:chmap.entrySet()){
                if (entry.getValue()>max){
                    max=entry.getValue();
                    topChar=entry.getKey();
                }
            }
            System.out.print(topChar+":"+max+"  ");
            chmap.remove(topChar);
        }
    }
}
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