The first character is cut off when BufferedReader is used

问题

This is the code :

File file = new File("Hello.txt");
file.createNewFile();
FileWriter write = new FileWriter(file);
BufferedWriter bufWrite = new BufferedWriter(write);
bufWrite.write("HelloWorld");
bufWrite.flush();
bufWrite.close();

FileReader read = new FileReader(file);
BufferedReader bufRead = new BufferedReader(read);
while(bufRead.read()!=-1){
 System.out.println(bufRead.readLine());
}
bufRead.close();

Here, the output is elloWorld. 'H'is not there. Why is it so? Not sure if I'm doing anything wrong here!

回答1:

It's a surprising common question.

When you do

bufRead.read()

you actually read a character, it doesn't put it back and let you read it again later.

The simplest solution is to not do this.

File file = new File("Hello.txt");
try (PrintWriter pw = new PrintWriter(new FileWriter(file))) {
    pw.println("HelloWorld"); // should have a new line
}

try (BufferedReader br = new BufferedReader(new FileReader(file))) {
    for (String line; (line = br.readLine()) != null; ) {
        System.out.println(line);
    }
}

回答2:

Look at your loop:

while(bufRead.read()!=-1){
 System.out.println(bufRead.readLine());
}

You're using read in the loop - which will consume the first character of the next line.

You should use:

String line;
while ((line = bufRead.readLine()) != null) {
    System.out.println(line);
}

回答3:

That has a very simple reason: The line

while(bufRead.read()!=-1){

consumes one character from the input stream. From the documentation:

Reads a single character. This method will block until a character is available, an I/O error occurs, or the end of the stream is reached.

回答4:

You already read a character at

while(bufRead.read()!=-1)

If there are more than one lines then it will vanish first character of every line!

so use

String line;
while ((line = bufRead.readLine()) != null) {
    System.out.println(line);
}

See read() readLine()

回答5:

bufRead.read() reads the first char.

Do bufRead.ready() instead.

来源：https://stackoverflow.com/questions/17950908/the-first-character-is-cut-off-when-bufferedreader-is-used

标签

java

file-io