读取文本文件中的字符串

Question

假设我的文本文件中有此文本：

VOTED/1/hannah/18
NOT VOTING/2/janice/20

我有这个代码：

File Orig_outFile = new File("C:\\voters.txt");
BufferedReader infile = new BufferedReader(new FileReader(Orig_outFile));

vNum=JOptionPane.showInputDialog("Enter voters number: ");
String line="";
String something="VOTED";
while(infile.readLine()!=null){
    line=infile.readLine();
    String [] info=line.split("/");

    if(info[1].matches(vNum)){
    while(info[0].matches(something)){
        JOptionPane.showMessageDialog(null, "Voter already voted or Voter not registered. Please try again");
        vNum=JOptionPane.showInputDialog("Enter voters number: ");
    }
    President();
    }
}
infile.close();

任务是用户需要输入一个投票人的号码，然后读取文本文件，然后如果发现文本文件中的info[0]包含VOTED会报错，需要输入又是选民的号码。我假设我的错误是我使用了两次 while 循环？

Answer 1

调用infile.readLine() 实际上是从文件中读取一行，将其返回并移至下一行。您调用它两次，一次在 while 循环条件中：

while(infile.readLine() != null)

再循环的第一行：

line = infile.readLine();

您应该只在 while 循环条件中调用它一次并将值分配给 line 变量，如下所示：

while((line = infile.readLine()) != null)

Answer 2

实际上，您正在通过执行infile.readLine() 读取while 中的一行，并通过再次执行infile.readLine() 将下一行附加到字符串line。

您最终只能从文件中读取第二行。您应该按如下方式更改您的 while 循环：

while((line = infile.readLine()) != null)

并删除以下语句：

line = infile.readLine();

这里是修正后的代码sn-p：

File Orig_outFile = new File("C:\\voters.txt");
BufferedReader infile = new BufferedReader(new FileReader(Orig_outFile));

vNum = JOptionPane.showInputDialog("Enter voters number: ");
String line = null;
String something = "VOTED";
while((line = infile.readLine()) != null) {
    String [] info = line.split("/");

    /* Assuming You Are Entering Voter's Number & Not Voter's Name */
    if(info[1].equalsIgnoreCase(vNum)) {
        if(info[0].equalsIgnoreCase(something)) {
            JOptionPane.showMessageDialog(null, "Voter already voted or 
                                          Voter not registered. Please try again");
            /* Please Note That You Are Currently Iterating File */
            /* If You Do This Here, You'll End Up Checking Same Records */
            /* You'll Have To Replace Outer `if` with `while` */
            vNum = JOptionPane.showInputDialog("Enter voters number: ");
        } else {
            President();
            break;
        }
    }
}
infile.close();

这是一个更清晰的实现方法：

1. 读取内存中的完整文件（最好是Map，带有键 -> 选民编号）。

2. 从用户那里获取选民编号并检查它是否存在于地图中。

3. 如果它在 Map 中不存在或值等于 VOTED，则重复 Step 2。

这里是sn-p的代码：

File Orig_outFile = new File("C:\\voters.txt");
BufferedReader infile = new BufferedReader(new FileReader(Orig_outFile));
Map<String,String> map = new HashMap<>();
String something = "VOTED";

String line = null;
while((line = infile.readLine()) != null) {
    String [] info = line.split("/");
    map.add(info[1],info[0]);
}
infile.close();

while(true) {
    vNum = JOptionPane.showInputDialog("Enter Voter's Number: ");
    if(map.contains(info[1]) && !map.get(info[1]).equalsIgnoreCase(something)) {
        President();
        break;
    } else {
        JOptionPane.showMessageDialog(null, "Voter already voted or 
                                          Voter not registered. Please try again");
    }
}