星期二

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.util.*;

public class Test {
    public static void main(String[] args) throws IOException {
            int n=0;
            Scanner sc=new Scanner(System.in);
            String s;
            int count=0;
            int num=1;
            //作为FileReader和FileWriter读取的对象
            String file1="D:\\哈利波特英文版\\HP7.txt";
            try
            {
                FileReader f=new FileReader(file1);
                BufferedReader a=new BufferedReader(f);
                StringBuffer c=new StringBuffer();

                //将文件内容存入StringBuffer中
                while((s = a.readLine())!=null)
                {
                    c.append(s);
                }
                //将StringBuffer转换成String，然后再将所有字符转化成小写字符
                String m=c.toString().toLowerCase();
                //匹配由数字和26个字母组成的字符串
                String [] d=m.split("[^a-zA-Z0-9]+");
                //"[^a-zA-Z0-9]+"
                //for(int i=0;i<d.length;i++)
                //{
                //    System.out.println(d[i]);
                //}
                //遍历数组将其存入Map<String, Integer>中
                Map<String , Integer> myTreeMap=new TreeMap<String, Integer>();
                for(int i = 0; i < d.length; i++) {
                    //containsKey()方法用于检查特定键是否在TreeMap中映射
                    if(myTreeMap.containsKey(d[i])) {
                        count = myTreeMap.get(d[i]);
                        myTreeMap.put(d[i], count + 1);
                    }
                    else {
                        myTreeMap.put(d[i], 1);
                    }
                }
                //通过比较器实现排序
                List<Map.Entry<String, Integer>> list = new ArrayList<Map.Entry<String, Integer>>(myTreeMap.entrySet());
                //按降序排序
                Collections.sort(list, new Comparator<Map.Entry<String, Integer>>() {

                    public int compare(Map.Entry<String, Integer> k1, Map.Entry<String, Integer> k2) {
                        //返回两个单词出现次数较多的那个单词的出现次数
                        return k2.getValue().compareTo(k1.getValue());
                    }

                });
                System.out.println("请输入N:");
                n=sc.nextInt();
                for(Map.Entry<String, Integer> map : list) {
                    if(num <= n) {
                        //输出到程序控制台
                        System.out.println(map.getKey() + ":" + map.getValue());
                        num++;
                    }
                    //输出完毕退出
                    else break;
                }
                //关闭文件指针
                a.close();
                // b.close();
            }
            catch(FileNotFoundException e)
            {
                System.out.println("找不到指定文件");
            }
            catch(IOException e)
            {
                System.out.println("文件读取错误");
            }
    }
}

输入N，输出单词出现前N个频率最多的