BufferedReader in Java

In Java, BufferedReader class is the most enhanced way to read the character or text data from the file/keyboard/network. The main advantage of BufferedReader compared to FileReader class is:- In addition to the single character, we can also read one line of data. The BufferedReader class is defined in the java.io package and it is a subclass of the Reader class. It is available from Java 1.1 version onwards.

public class BufferedReader
extends Reader

Constructors of BufferedReader class

Since BufferedReader is a connection based, where one end is a Java application and another end is a file or keyboard. We must always pass that information to the constructor. Therefore, it doesn’t contain 0 parameter constructor.

It contains two constructors,

• public BufferedReader(Reader in)
• public BufferedReader(Reader in, int size)

BufferedReader can’t communicate file or keyboard directly, it can communicate via some Reader object. We generally use FileReader class to communicate with the file, and InputStreamWriter class to communicate with the keyboard. FileWriter and FileReader class can directly communicate with the file. OuputStreamReader is a bridge from character streams to byte streams and InputStreamReader is a bridge from byte streams to character streams.

BufferedReader Methods

In BufferedReader class important methods are given,

Modifier and Type	Method	Desription
int	read()	It reads a single character at a time.
int	read(char[] ch, int off, int len)	Reads characters into a portion of an array.
String	readLine()	It reads a line of text.
long	skip(long n)	It skips characters.
boolean	ready()	tells whether this stream is ready to be read.
boolean	markSupported()	tells whether this stream supports the mark() operation.
void	mark(int readAheadLimit)	It marks the present position in the stream.
void	reset()	It resets the stream to the most recent mark.

All these methods throws IOException when an input or output error occurs.

BufferedReader readLine() method

The readLine() method is the most important method of BufferedReader class. It reads a line of text. A line is considered to be terminated by any one of a line feed (‘\n’), a carriage return (‘\r’), a carriage return followed immediately by a line feed, or by reaching the end-of-file (EOF).

It returns a string containing the contents of the line, not including any line-termination characters, or null if the end of the stream has been reached without reading any characters. It throws IOException when an input or output error occurs.

BufferedReader Object Creation Syntax

To connect BufferedReader object to file,

• create a FileReader object by passing a valid file name.
• create a BufferedReader object by using FileReader class object.

Syntax of BufferedReader to connect to file is,

// create BufferedReader and FileReader object
FileReader fr = new FileReader("filename.txt");
BufferedReader br = new BufferedReader(fr);

Or, it can be written in single line as,

// In single line,
BufferedReader br=new BufferedReader(new FileReader("filename.txt"));

To connect BufferedReader object with Keyboard,

• pass System.in as argument to InputStreamReader object creation
• pass InputStreamReader object as argument to BufferedReader object creation

Syntax of BufferedReader to connect to keyboard is,

// create BufferedReader and InputStreamReader object
InputStreamReader isr = new InputStreamReader(System.in);
BufferedReader br = new BufferedReader(isr);

Or, it can be written in single line as,

// In one line 
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));

Java BufferedReader readline

We can use the BufferedReader class to read a complete line using the readLine() method. The file “data.txt” is available in the current directory. The character in the “data.txt” is,

10 20 30 40 50 60 70
Hello, World!
20.5 99.99

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

   public static void main(String[] args) 
                    throws IOException {

      // create BufferedReader and FileReader object
      FileReader fr = new FileReader("data.txt");
      BufferedReader br = new BufferedReader(fr);

      // read line from the file
      String line = br.readLine();
      while (line != null) {
      	// display
      	System.out.println(line);
      	line = br.readLine();
      }

      // close stream
      br.close();
   }
}

Whenever we are closing BufferedReader then automatically internal FileReader also will be closed and we are not required to close them expliclitly.

The logic for the same program also can be written as,

// create BufferedReader object
BufferedReader br = new BufferedReader(new FileReader("data.txt"));
// read line from the file
String line;
while ((line = br.readLine()) != null) {
   // display
   System.out.println(line);
}
// close stream
br.close();

Instead foe checking null we can also call the ready() method. The ready() method tells whether this stream is ready to be read.

// read line from the file and display
while (br.ready()) {
   System.out.println(br.readLine());
}

Same program using above logic,

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
public class BufferedReaderDemo {
   public static void main(String[] args) 
                    throws IOException {

      // create BufferedReader and FileReader object
      BufferedReader br = new BufferedReader(
                      new FileReader("data.txt"));

      // read line from the file and display
      while (br.ready()) {
         System.out.println(br.readLine());
      }

      // close stream
      br.close();
   }
}

InputStreamReader and BufferedReader in Java

If we want to read data from the keyboard at runtime while using BufferedReader then we must use InputStreamReader class. InputStreamReader is a bridge from byte streams to character streams. Keyboard given values are passed as binary form and InputStream converts them to String. Finally, BufferedReader can read them as String values.

How to take integer input from user in Java using bufferedreader? Below is the Java program to read data from keyboard using InputStreamReader and BufferedReader,

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
public class BufferedReaderDemo {
   public static void main(String[] args) 
                    throws IOException {

      // create BufferedReader object
      BufferedReader br = new BufferedReader(
      	   new InputStreamReader(System.in));

      // read one line from the console
      System.out.print("Enter data: ");
      String str = br.readLine();

      // display data
      System.out.println("Entered data is: ");
      System.out.println(str);

      // close stream
      br.close();
   }
}

Output for run-1:-

Enter data: 10 20 30 40.5 22.9
Entered data is:
10 20 30 40.5 22.9

Output for run-2:-

Enter data: Hello, World!
Entered data is:
Hello, World!

Program to Add Two Number

Java program to add two numbers by reading its values from the keyboard.

Procedure,
1) Create a BufferedReader object using InputStreamReader by passing System.in
2) Read the first number and store into a string
3) Read the second number and store into the string
4) Convert string to a number, if stored values can’t be converted to a number then it throws NumberFormatException, and program execution terminates
5) Add both values and display them.

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
public class BufferedReaderDemo {
  public static void main(String[] args) throws IOException {
      // create BufferedReader object
      BufferedReader br = new BufferedReader(
                       new InputStreamReader(System.in));

      // read data from the console
      System.out.print("Enter first integer value: ");
      String firstNumber = br.readLine();
      System.out.print("Enter second integer value: ");
      String secondNumber = br.readLine();

      // convert string to integer
      int n1 = Integer.parseInt(firstNumber);
      int n2 = Integer.parseInt(secondNumber);

      // calculate sum value
      int sum = n1 + n2;

      // display result
      System.out.println("Sum= " + sum);

      // close stream
      br.close();
  }
}

Output:-

Enter first integer value: 10
Enter second integer value: 20
Sum= 30

In the above program, we are directly converting the input value to int type value, if it is not a valid int type value then it will throw NumberFormatException. Example with input/output,

Enter first integer value: a
Enter second integer value: b
Exception in thread “main” java.lang.NumberFormatException: For input string: “a”

To solve this problem we can use Exception handling concept. We can use the try-catch block or try-with resources. Below program uses try-catch block.

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;

public class BufferedReaderDemo {
  public static void main(String[] args) {

    // create BufferedReader object
    BufferedReader br = new BufferedReader(
        new InputStreamReader(System.in));

    try {
      // read data from the console
      System.out.print("Enter first integer value: ");
      String firstNumber = br.readLine();
      System.out.print("Enter second integer value: ");
      String secondNumber = br.readLine();

      // convert string to integer
      int n1 = Integer.parseInt(firstNumber);
      int n2 = Integer.parseInt(secondNumber);

      // calculate sum value
      int sum = n1 + n2;

      // display result
      System.out.println("Sum= " + sum);

    } catch (NumberFormatException nfe) {
      System.out.println("Pass only integer numbers");
      nfe.printStackTrace();
    } catch (IOException ioe) {
      ioe.printStackTrace();
    } 
    finally {
      // close stream
      try {
        if(br != null) br.close();
      } catch(IOException ioe) {
        ioe.printStackTrace();
      }
    }
  }
}

Test with invalid inputs,

Enter first integer value: a
Enter second integer value: b
Pass only integer numbers
java.lang.NumberFormatException: For input string: “a”

Important points

Since all data are read as String, therefore converting from String to primitive type is the most important work while working with BuffereReader class. The different methods to convert string to primitives are given below. Assume “line” is a variable of String type.

Return Type	Method
int	Integer.parseInt(line)
long	Long.parseLong(line)
float	Float.parseFloat(line)
double	Double.parseDouble(line)
boolean	Boolean.parseBoolean(line)
char[]	line.toCharArray()

Another important work is to convert lines into tokens. For this, we can use the split() method of the String class. Let us understand it through an example.

Input:-

10 20 30 40 50

Problem description:- Read these values using readLine() of BufferedReader and store them to an int array.

We know that readLine() read one line at a time as a String.

// read line,
 String line = br.readLine();

Currently, line = “10 20 30 40 50″. Now, split this string based on the space(” “), using split() method of the String class.

// split into String array
 String str[] = line.split(" ");

Now,
str[0] = “10”;
str[1] = “20”;
str[2] = “30”;
str[3] = “40”;
str[4] = “50”;

Using Integer.parseInt() we can convert them to int type value. To store them in an array, first, create an int type array with a size of the str[] array.

// create int array with given size
 int arr[] = new int[str.length];

Currently,
arr[0] = 0;
arr[1] = 0;
arr[2] = 0;
arr[3] = 0;
arr[4] = 0;

// Convert str[i] to int and 
 // assign them to array
 for (int i = 0; i < size; i++) {
   arr[i] = Integer.parseInt(str[i]);
 }

Finally,
arr[0] = 10;
arr[1] = 20;
arr[2] = 30;
arr[3] = 40;
arr[4] = 50;

Java Bufferedreader Example

Java program to find sum of array elements using BufferedReader,

Program description:- Write a Java program to find the sum of array elements. The array size and elements will be given by the end-user, read those input values using BufferedReader class. In input, the first line gives the size of the array, and the second line contains array elements.

Sample Input,

5
10 20 30 40 50

Expected Output,

150

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class BufferedReaderDemo {
  public static void main(String[] args) 
                        throws IOException {

    // create BufferedReader object
    BufferedReader br = new BufferedReader(
        new InputStreamReader(System.in));

    // read size of the array (first line)
    String line1 = br.readLine();
    // convert String to int type
    int size = Integer.parseInt(line1);

    // create int array object with given size
    int arr[] = new int[size];

    // read array elements (second line)
    String line2 = br.readLine();
    // convert line2 to tokens
    String[] str = line2.split(" ");

    // update array
    for (int i = 0; i < size; i++) {
      // convert string str[i] to int
      // and assign to array element arr[i]
      arr[i] = Integer.parseInt(str[i]);
    }

    // calculate sum of array elements
    int sum = 0;
    for (int i = 0; i < size; i++) {
      sum = sum + arr[i];
    }

    // display result (sum of array elements)
    System.out.println(sum);

    // close the stream
    br.close();
  }
}

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