02-Reading-Console-Input.md

Reading Console Input

In Java, console input is accomplished by reading from System.in. To obtain a characterbased stream that is attached to the console, wrap System.in in a BufferedReader object. BufferedReader supports a buffered input stream.

BufferedReader(Reader inputReader)

Here, inputReader is the stream that is linked to the instance of BufferedReader that is being created.

InputStreamReader converts bytes to characters. To obtain an InputStreamReader object that is linked to System.in, use the following constructor:

InputStreamReader(InputStream inputStream)

Putting it all together, the following line of code creates a BufferedReader that is connected to the keyboard:

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

Reading Characters

To read a character from a BufferedReader, use read( ). The version of read( ) that we will be using is

int read( ) throws IOException

Each time that read() is called, it reads a character from the input stream and returns it as an integer value. It returns –1 when the end of the stream is encountered. As you can see, it can throw an IOException.

Example 01

// Use a BufferedReader to read characters from the console.
import java.io.*;
class BRRead {
    public static void main(String args[]) throws IOException {
        char c;
        BufferedReader br = new
        BufferedReader(new InputStreamReader(System.in));
        System.out.println("Enter characters, 'q' to quit.");
        // read characters
        do {
            c = (char) br.read();
            System.out.println(c);
        } while(c != 'q');
    }
}

Output

Enter characters, 'q' to quit.
123abcq
1
2
3
a
b
c
q

Reading Strings

To read a string from the keyboard, use the version of readLine() that is a member of the BufferedReader class. Its general form is shown here:

String readLine() throws IOException

Example 02

// A tiny editor.
import java.io.*;
class TinyEdit {
    public static void main(String args[]) throws IOException {
        // create a BufferedReader using System.in
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String str[] = new String[100];
        System.out.println("Enter lines of text.");
        System.out.println("Enter 'stop' to quit.");
        for(int i=0; i<100; i++) {
            str[i] = br.readLine();
            if(str[i].equals("stop")) 
                break;
        }
        System.out.println("\nHere is your file:");
        // display the lines
        for(int i=0; i<100; i++) {
            if(str[i].equals("stop"))
                break;
            System.out.println(str[i]);
        }
    }
}

Output

Enter lines of text.
Enter 'stop' to quit.
This is line one.
This is line two.
Java makes working with strings easy.
Just create String objects.
stop
Here is your file:
This is line one.
This is line two.
Java makes working with strings easy.
Just create String objects.

External Resources

Readings

• Oracle Tutorials
• JavaTPoint
• GeeksForGeeks - Scanner Class
• GeeksForGeeks - Scanner vs BufferedReader

More Examples and Practice Questions

Provided in the last chapter of current section.