Java 用hashmap统计词频

C:\\Temp\\1\\a.txt   内容：

1,a,282,b,353,c,284,d,355,e,286,a,287,b,358,c,289,a,28

public class FileTest{    static File filea = new File("C:\\Temp\\1\\a.txt");    static HashMap<String,Integer> hashmap = new HashMap<String,Integer>();    public static void main(String[] args) throws IOException    {          BufferedReader bra = new BufferedReader(new FileReader(filea));          Scanner sa = new Scanner(bra);                while(sa.hasNextLine()){             String line = sa.nextLine();            String name = line.split(",")[1];                        if (hashmap.containsKey(name))                 hashmap.put(name, hashmap.get(name) + 1);              else               hashmap.put(name, 1);          }                  for (Entry<String, Integer> entry : hashmap.entrySet()){            Object key = entry.getKey();            Object val = entry.getValue();                        System.out.println(key.toString() + " " + val.toString());            }                        }}        

打印

d 1
e 1
b 2
c 2
a 3

注意遍历hashmap的遍历：

a. HashMap的循环，如果既需要key也需要value，直接用

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Map<String, String> map = new HashMap<String, String>();

for (Entry<String, String> entry : map.entrySet()) {

entry.getKey();

entry.getValue();

}

b. 如果只是遍历key而无需value的话，可以直接用

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Map<String,String>map=newHashMap<String,String>();

for(Stringkey:map.keySet()){

}