Question

当我尝试编译时，为什么hasNext行会返回错误？

public static void main(String args[]) throws Exception
{

    BufferedReader infile = new BufferedReader(new FileReader( "woodchuck.txt" ));

    HashMap<String, Integer> histoMap = new HashMap<String,Integer>();

    String word;
    while((infile.hasNext()) !=null)
    {

        if(histoMap.get(word)==null)
            histoMap.put(word,1);
        else
            histoMap.put(word, histoMap.get(word)+1);
    }
    infile.close();
    System.out.print(histoMap);
}

Answer 1

BufferedReader未提供方法hasNext()。相反，只要文件结束，readLine()就会返回null。由于你没有阅读任何内容，你的代码包含了一个无限循环。

Answer 2

切换到readLine()并将作业添加到word足以让它输出结果：

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

public class ReadFile {
    public static void main(String args[]) throws Exception
    {
        try(BufferedReader infile = new BufferedReader(new FileReader("woodchuck.txt"))) 
        {
            HashMap<String, Integer> histoMap = new HashMap<String,Integer>();

            String word;
            while((word = infile.readLine()) != null)
            {
                if(histoMap.get(word) == null)
                    histoMap.put(word,1);
                else
                    histoMap.put(word, histoMap.get(word)+1);
            }
            System.out.print(histoMap);
        } 
        catch (FileNotFoundException e) 
        {
            String pwd = System.getProperty("user.dir") + "\\";
            FileNotFoundException e2 = new FileNotFoundException(pwd + e.getMessage());
            e2.initCause(e);
            throw e2;
        } 
    }
}

添加try-with-resources即使发生异常也会确保infile关闭。

我添加了工作目录，因为它非常方便地知道它找不到文件的确切位置。在硬编码非完全限定路径的文件名时很有用。

如何正确使用hasNext？

2 个答案: