读取文本文件中的字符串

Question

假设我的文本文件中有以下文本：

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选民号码，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就会报错消息并需要再次输入其选民号码。我假设我在这里的错误是我使用了 while 循环两次？

Answer 1

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

您最终只读取了文件的第二行。您应该按如下方式更改 while 循环：

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

并删除以下语句：

line = infile.readLine();

这是更正后的代码片段：

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();

这里有一个更清晰的实现方法：

读取内存中的完整文件（最好是 Map with key -> Voter Number）。
从用户那里获取选民编号并检查它是否存在于地图中。
如果Map中不存在或者值等于VOTED则重复Step 2.

这是代码片段：

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");
    }
}

Answer 2

调用infile.readLine()实际上是从文件中读取一行，returns它并移动到下一行。您调用了两次，一次是在 while 循环条件中：

while(infile.readLine() != null)

在循环的第一行再次：

line = infile.readLine();

您应该只在 while 循环条件中调用一次并将值赋给 line 变量，如下所示：

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

读取文本文件中的字符串

read a String in a text file

java

file-handling

bufferedreader