Dialog and Console Input-Output
Posted on: July 26, 2006 at 12:00 AM
Posted on: July 26, 2006 at 12:00 AM
This is similar to the previous program, but it also gets input from the user.
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Java Notes
Dialog and Console Input-Output
This is similar to the previous program, but it also gets input from the user.
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// Description: This program gets a string from a dialog box.
// File: dialogInputOutput/ThirdProgram.java
// Author: Michael Maus
// Date: 29 Jan 2005
import javax.swing.*;
public class ThirdProgram {
public static void main(String[] args) {
String humanName; // A local variable to hold the name.
humanName = JOptionPane.showInputDialog(null, "What's your name, Earthling");
JOptionPane.showMessageDialog(null, "Take me to your leader, " + humanName);
}
}
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- Line 11 - Declaring a local variable.
- This tells the compiler to reserve some memory to hold a String. It's going to hold a name, so we called the variable (a place in the computer's memory) "humanName". The syntax for a simple declaration is to write the type of thing that a variable will hold (String in this case), followed by the variable name (humanName in this case).
- Line 13 - Asking the user for a String.
JOptionPane'sshowInputDialogmethod displays a message in a dialog box that also accepts user input. It returns a string that can be stored into a variable.This is an assignment statement. The part to the right of the "=" must produce a value, and this value is then stored in the variable on the left (humanName).
- Line 15 - Putting two strings together (concatenation)
Concantenation, indicated by the plus sign (+), puts two strings together to build a bigger string, which is then passed as a parameter. The plus sign (+) is also used for addition of numbers. 
Console Input: Scanner
The java.util.Scanner class (added in Java 5) allows simple console and file input. Of course, your program should eventually have a GUI user interface, but Scanner is very useful for reading data files.
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// File : introductory/IntroScanner.java // Purpose: Write to and read from the console. // Author : Michael Maus // Date : 2006-01-20 import java.util.*; //Note 1 public class IntroScanner { public static void main(String[] args) { //... Initialization String name; // Declare a variable to hold the name. Scanner in = new Scanner(System.in); //... Prompt and read input. System.out.println("What's your name, Earthling?"); name = in.nextLine(); // Read one line from the console. in.close(); //Note 2 //... Display output System.out.println("Take me to your leader, " + name); } } |
Notes
- Altho we only need the Scanner class from the java.util package, the most common programming style is to make all classes (*) visible.
- Closing the console isn't really necessary, but it's a good habit. If we had been reading a file, which is common with Scanner, closing it would be important.