Simple Input/Output in Java

This page gives a quick overview of simple interactive input and output techniques for Java programs in CS 2.

"Import"-ant

The following import statements are required for the code below.

import java.io.*; //needed for console i/o
import javax.swing.*; //needed for gui (pop up) interfaces

Command line input

Command line input to a program is through the argument list from the Unix/DOS command. You need to have the String array parameter in your main method:

public class myClass {
...
    public static void main (String args[ ]) {
      // args[0] is a string of the first argument (delimited by blanks)
      // args[1] is a string of the second argument
     System.out.println ("The second argument in the command line is "+args[1]);
...}
}

Console input/output

This is input and output within a DOS window or at the Java Console (if your browser has the console enabled and displayed). This is typically associated with Java applications, although applets can perform console I/O as well.

Console output

• System.out.print(string); //permits subsequent print to continue on the same line
• System.out.println(string); //adds the newline codes to the end of the string.

Console input

This section describes how to read lines from the console. Very simple input from the console is limited to character-by-character input.

Any routine that uses the bufferedReader class is requred to handle/throw the IOException as well.

...
public static void main(String [] args) throws IOException {
...
    String line; // hold the input line
    BufferedReader input = new BufferedReader( new InputStreamReader(System.in));
...
     line = input.readLine(); //read first line
...  //process line
    line = input.readLine(); //get second line
...  //process it

Pop up window input/output

Pop up window input

String input;

input = JOptionPane.showInputDialog("prompt string");

Pop up window output

JOptionPane.showMessageDialog(null, "messageString",
        "titleOfBox",    JOptionPane.INFORMATION_MESSAGE);