Java Tutorial/File/BufferedReader

BufferedReader

1. BufferedReader wraps another Reader and improves performance.
2. BufferedReader provides a readLine method to read a line of text.

Using BufferedReader:

   <source lang="java">

InputStreamReader inputStreamReader = new InputStreamReader(new FileInputStream (textFile), encoding ); BufferedReader bufferedReader = new BufferedReader (inputStreamReader);</source>

Call the static method PressAnykey to keep to DOS window open.

   <source lang="java">

import java.io.BufferedReader; import java.io.InputStreamReader; public class Main{

 public static void main(String[] args) {
   PressAnyKey();
 }
 public static void PressAnyKey() {
   BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
   System.out.print("Press any key...");
   try {
     input.readLine();
   } catch (Exception e) {
     e.printStackTrace();
   }
 }

}</source>

Create BufferedReader from FileReader

   <source lang="java">

import java.io.BufferedReader; import java.io.FileReader; import java.io.IOException; public class MainClass {

 public static void main(String[] args) throws IOException {
   // 1. Reading input by lines:
   BufferedReader in = new BufferedReader(new FileReader("IOStreamDemo.java"));
   String s, s2 = new String();
   while ((s = in.readLine()) != null)
     s2 += s + "\n";
   in.close();
 }

}</source>

Create BufferedReader from InputStreamReader

   <source lang="java">

import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; public class MainClass {

 public static void main(String[] args) throws IOException {
   BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in));
   System.out.print("Enter a line:");
   System.out.println(stdin.readLine());
 }

}</source>

Create BufferReader from InputStreamReader

   <source lang="java">

import java.io.BufferedReader; import java.io.InputStreamReader; import java.io.ObjectOutputStream; import java.net.Socket; import java.util.Locale; public class DateClient {

 final static int PORT = 5000;
 public static void main(String[] args) {
   try {
     Socket s = new Socket("localhost", PORT);
     ObjectOutputStream oos;
     oos = new ObjectOutputStream(s.getOutputStream());
     oos.writeObject(Locale.getDefault());
     InputStreamReader isr;
     isr = new InputStreamReader(s.getInputStream());
     BufferedReader br = new BufferedReader(isr);
     System.out.println(br.readLine());
   } catch (Exception e) {
     System.err.println(e);
   }
 }

}</source>

Create PrintWriter from BufferedWriter

   <source lang="java">

import java.io.BufferedReader; import java.io.BufferedWriter; import java.io.EOFException; import java.io.FileWriter; import java.io.IOException; import java.io.PrintWriter; import java.io.StringReader; public class MainClass {

 public static void main(String[] args) throws IOException {
   try {
     BufferedReader in4 = new BufferedReader(new StringReader("asdf"));
     PrintWriter out1 = new PrintWriter(new BufferedWriter(new FileWriter("IODemo.out")));
     int lineCount = 1;
     String s = null;
     while((s = in4.readLine()) != null )
       out1.println(lineCount++ + ": " + s);
     out1.close();
   } catch(EOFException e) {
     System.err.println("End of stream");
   }
 }

}</source>

Read content of a file

   <source lang="java">

import java.io.BufferedReader; import java.io.File; import java.io.FileReader; public class Main {

 public static void main(String[] argv) {
   readTextFile(new File("c:\\a.txt"));
 }
 public static String readTextFile(File filename) {
   try {
     BufferedReader br = new BufferedReader(new FileReader(filename));
     StringBuilder sb = new StringBuilder();
     String line = br.readLine();
     while (line != null) {
       sb.append(line + "\n");
       line = br.readLine();
     }
     br.close();
     return sb.toString();
   } catch (Exception e) {
     e.printStackTrace();
     System.err.println(filename);
     System.err.println(e);
     return "";
   }
 }

}</source>

Reading Text from a File

   <source lang="java">

import java.io.BufferedReader; import java.io.FileReader; public class Main {

 public static void main(String[] argv) throws Exception {
   BufferedReader in = new BufferedReader(new FileReader("infilename"));
   String str;
   while ((str = in.readLine()) != null) {
     System.out.println(str);
   }
   in.close();
 }

}</source>

Reads a text file and displays it line by line.

   <source lang="java">

import java.io.BufferedReader; import java.io.File; import java.io.FileReader; public class MainClass {

 public static void main(String[] a) {
   FileReader fr;
   try {
     fr = new FileReader (new File("yourFile.txt"));
     BufferedReader br = new BufferedReader (fr);
     String line = br.readLine();
     while (line != null) {
         System.out.println(line);
         line = br.readLine();
     }
     br.close();
     
   } catch (Exception e) {
     // TODO Auto-generated catch block
     e.printStackTrace();
   }

 }

}</source>

Reversing a File

   <source lang="java">

import java.io.BufferedReader; import java.io.BufferedWriter; import java.io.FileReader; import java.io.FileWriter; import java.io.IOException; import java.io.PrintWriter; import java.util.ArrayList; import java.util.Collections; import java.util.Iterator; public class ReverseLines {

 public static void main(String[] args) {
   try {
     BufferedReader input = new BufferedReader(new FileReader(args[0]));
     ArrayList list = new ArrayList();
     String line;
     while ((line = input.readLine()) != null) {
       list.add(line);
     }
     input.close();
     Collections.reverse(list);
     PrintWriter output = new PrintWriter(new BufferedWriter(new FileWriter(args[1])));
     for (Iterator i = list.iterator(); i.hasNext();) {
       output.println((String) i.next());
     }
     output.close();
   } catch (IOException e) {
     System.err.println(e);
   }
 }

}</source>

Using BufferedReader to read input number from user

   <source lang="java">

import java.io.BufferedReader; import java.io.InputStreamReader; public class Main {

 public static void main(String[] args) throws Exception {
   BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
   String input = reader.readLine();
   double number = Double.parseDouble(input);
   System.out.println(input + ":" + Math.sqrt(number));
   reader.close();
 }

}</source>