PrintStream 只打印输入文件的最后一行 [英] PrintStream Only Printing out the Last Line of Input File

问题描述

我有这个代码

public class program {
    public static void main(String[] args) {
        try {
            String filePath = (args[0]);
            String strLine;

            BufferedReader br = new BufferedReader(new FileReader(filePath));

            //Read File Line By Line and Print the content on the console
            while ((strLine = br.readLine()) != null) {
            //System.out.println (strLine);
            PrintStream out = new PrintStream(new FileOutputStream( //printing output to user specified text file (command line argument: outputfile)
                    args[1]+".txt"));   
                out.print(strLine);
            }
            //close the streams
            br.close();
            }
            catch(IOException e){
            System.err.println("An IOException was caught :"+e.getMessage());
            }

    }
}

如果我使用 java program input.txt 输出从命令行调用这个程序

If I invoke this program from the command line using java program input.txt output

如果输入文件内容是这样的:你好你好再见

and if input file contents were this: hello hi bye

输出文件将打印:再见

它只打印输出的最后一行.

It is only printing the last line of the output.

如果代替:

  PrintStream out = new PrintStream(new FileOutputStream( //printing output to user specified text file (command line argument: outputfile)
                args[1]+".txt"));   
            out.print(strLine);

我只有

System.out.println (strLine);

在 while 循环中，它将正确地将输入文件中的每一行打印到控制台.

within the while loop, then it would correctly print each line from the input file to the console.

为什么当我尝试将其打印到另一个文件时，它只打印最后一行?

Why when I try to print it to another file it only prints the last line?

推荐答案

不要在每个循环中创建新的 PrintStream.而是在 while 循环之前创建 PrintStream:

Don't create a new PrintStream in each loop. Instead create the PrintStream prior to the while loop:

PrintStream out = new PrintStream( ... );
while ((strLine = br.readLine()) != null) {
  out.print(strLine);
}            

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