Access value Outside While loop

Question

I am reading an entire file and I want to use the line if it contains a specific string. I am unable to use the string because it is printing null outside the while loop, despite the fact that I have initialized it outside the loop.

FileInputStream wf = new FileInputStream(pr.getSplitDir() + listfiles[i]);
BufferedReader wbf = new BufferedReader(new InputStreamReader(wf));
String wfl = "";
while ((wfl = wbf.readLine()) != null) {
    if (wfl.contains("A/C NO:")){
        // System.out.println(wfl); // Here it is Printing the correct line
    }
}
System.out.println(wfl); // Here it is printing null

Please help.

Answer 1

Try this below, You have to use another String or StringBuilder to get final out put

     FileInputStream wf = new FileInputStream(pr.getSplitDir() + listfiles[i]);
        BufferedReader wbf = new BufferedReader(new InputStreamReader(wf));
        String wfl = "";
        StringBuilder sb = new StringBuilder();
        while ((wfl = wbf.readLine()) != null) {
            if(wfl.contains("A/C NO:")){
                //System.out.println(wfl);//Here it is Printing the correct line
                sb.append(wfl);
            }
        }
        System.out.println(sb.toString());//Here it is printing null

Answer 2

 while ((wfl = wbf.readLine()) != null) {
                if(wfl.contains("A/C NO:")){
                    //System.out.println(wfl);//Here it is Printing the correct line

                }
            }

Your while loop will exit only when wfl is null . So you have your answer!

Answer 3

Because your wbf.readLine when read null ,it assigns it wfl too and then compares to null

while ((wfl = wbf.readLine()) != null) {  // here wbf.readLine when read null assigns to wfl
  if(wfl.contains("A/C NO:")){
        //System.out.println(wfl);//Here it is Printing the correct line
     }
 }

Do it like this,if you want to print outside while loop,

String test ="";
String wfl ="";
while ((wfl = wbf.readLine()) != null) {
      if(wfl.contains("A/C NO:")){
            //System.out.println(wfl);//Here it is Printing the correct line
      }

      test = test + wfl ; // for assigning all line
      //test = wfl // for assigning last line
}



 System.out.println(test); // it wil print the correct line

Answer 4

要停止，你的循环需要wfl为null ，所以当你的循环刚刚停止时， wfl显然是null 。