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#004 Getting input from keyboard

by nobaksan

Lab Exercises

 

Exercise 1: Getting input from keyboard via BufferedReader class

In this exercise, you are going to build a simple interactive Java application, which gets user entered input data from keyboard. The program will use BufferedReader and InputStreamReader classes to receive the intput data. (You don’t really need to understand in detail how these classes work, however.)  You will also learn how to use Javadoc to get more information on Java classes.

(1.1) Build and run GetInputFromKeyboard Java program

1. Create a NetBeans project

  • Select File from top-level menu and select New Project.
  • Observe that the New Project dialog box appears.
  • Select Java under Categories section and Java Application under Projects section.
  • Click Next.

  • Under Name and Location pane, for the Project Name field, enter MyGetInputFromKeyboardProject.
  • For the Create Main Class field, enter GetInputFromKeyboard.  (Figure-1.10 below)
  • Click Finish.


Figure-1.10: Create MyGetInputFromKeyboardProject

  • Observe that the MyGetInputFromKeyboardProject project node is created under Projects pane of the NetBeans IDE and IDE generated GetInputFromKeyboard.java is displayed in the editor window of the IDE.
2. Modify the IDE generated GetInputFromKeyboard.java  as shown in Code-1.11 below. Study the code by paying special attention to the bold-fonted comments.  For now, don’t worry about the details of the BufferedReader and InputStreamReader classes for now.
/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/

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

/**
*
* @author sang
*/
public class GetInputFromKeyboard {

/**
* @param args the command line arguments
*/
public static void main(String[] args) {

// Create BufferedReader object from Standard input device.
// Standard input device is typically a keyborad.
BufferedReader dataIn = new BufferedReader(new
InputStreamReader( System.in) );

// Prompt a user to enter his/her name
String name = “”;
System.out.println(“Please Enter Your Name:”);

// Read data into name variable
try{
name = dataIn.readLine();
}catch( IOException e ){
System.out.println(“Error!”);
}

// Display the name
System.out.println(“Hello ” + name +”!”);
}

}

Code-1.11: GetInputFromKeyboard.java

3. Build and run the program

  • Right click MyGetInputFromKeyboardProject and select Run.
  • Observe that the program is expecting a user input.
  • Type in your name, Sang Shin, in this example and press Enter key.  Make sure you do not click Close Input. (Figure-1.12 below)


Figure-1.12: Enter value

  • Observe that Hello <whatever name you entered>, in this example Hello Sang Shin is displayed in the Output window of the IDE.  (Figure-1.13 and Figure-1.14 below)
Please Enter Your Name:
Sang Shin
Hello Sang Shin!

Figure-1.13: Result


Figure-1.14: Display the data that was entered

4. Modify the GetInputFromKeyboard.java to read your age as shown in Code-1.15 below. The code fragment that needs to be added is highlighted in bold and blue-colored font.

/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/

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

/**
*
* @author sang
*/

public class GetInputFromKeyboard {

/**
* @param args the command line arguments
*/
public static void main(String[] args) {

// Create BufferedReader object from Standard input device.
// Standard input device is typically a keyboard.
BufferedReader dataIn = new BufferedReader(new
InputStreamReader( System.in) );

// Prompt a user to enter his/her name
String name = “”;
System.out.println(“Please Enter Your Name:”);

// Read entered data into name variable
try{
name = dataIn.readLine();
}catch( IOException e ){
System.out.println(“Error!”);
}

// Display the name
System.out.println(“Hello ” + name +”!”);

// Prompt a user to enter his/her age
String age= “”;
System.out.println(“Please Enter Your Age:”);

// Read entered data into age variable
try{
age = dataIn.readLine();
}catch( IOException e ){
System.out.println(“Error!”);
}

// Display the name and age
System.out.println(“Hello ” + name +”!” + ” ” + “Your age is ” + age);
}

}

Code-1.15: Add code to prompt a user to enter age

5. Build and run the program

  • Right click MyGetInputFromKeyboardProject and select Run.
  • Observe that the program is expecting a user input.
  • Type in your name, Sang Shin, in this example and press Enter key.  Make sure you do not click Close Input.
  • Type in your age, 100, in this example and press Enter key.  Make sure you do not lock Close Input.
  • Observe that Hello <whatever name you entered>, in this example Hello Sang Shin is displayed in the Output window of the IDE.  (Figure-1.16 below)
Please Enter Your Name:
Sang Shin
Hello Sang Shin!
Please Enter Your Age:
100
Hello Sang Shin! Your age is 100

Figure-1.16: Display of name and age

(1.2) Convert user entered “String” type value to “int” type value

Now suppose you want to add the following logic to the program.

If the entered age is over 100, display
Hello <name>, you are old!
Otherwise
Hello <name>, you are young!

Notice in the previous code, your program received the age in the form of String type.  And you cannot compare String type “99” with int primitive type of 100.  In other words, you have to convert the String type of “99” to int type of 99 before you compare it against another int type 100.

Fortunately, there is a method called parseInt() in the Integer class for converting String type into int type.

1. See the JavaDoc of Integer class.

  • From your browser, go to  http://java.sun.com/j2se/1.6.0/docs/api/
  • Observe that Javadoc root page gets dispayed.
  • Scroll down in order to see the Integer class in the lower left box.
  • Click Integer.
  • Observe that Javadoc of the Integer class gets displayed in the right pane of the browser. (Figure-1.20 below)


Figure-1.20: Javadoc of Integer class

  • Scroll down to see the parseInt(String s) method.
  • Observe that it is a static method.  (Figure-1.21 below)


Figure-1.21: Javadoc of the parseInt(String s) method

  • Click the hyperlink of the parseInt(String s) method.
  • Observe that the detail information of the method gets displayed. (Figure-1.22 below)
  • Note that the method throws NumberFormatException.


Figure-1.22: Detail information on parseInt(String s) method

2. Modify the GetInputFromKeyboard.java to read your age as shown in Code-1.23 below. The code fragment that needs to be added is highlighted in bold and blue-colored font.

/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/

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

/**
*
* @author sang
*/
public class GetInputFromKeyboard {

/**
* @param args the command line arguments
*/
public static void main(String[] args) {

// Create BufferedReader object from Standard input device.
// Standard input device is typically a keyboard.
BufferedReader dataIn = new BufferedReader(new
InputStreamReader( System.in) );

// Prompt a user to enter his/her name
String name = “”;
System.out.println(“Please Enter Your Name:”);

// Read entered data into name variable
try{
name = dataIn.readLine();
}catch( IOException e ){
System.out.println(“Error!”);
}

// Display the name
System.out.println(“Hello ” + name +”!”);

// Prompt a user to enter his/her age
String age= “”;
System.out.println(“Please Enter Your Age:”);

// Read entered data into age variable
try{
age = dataIn.readLine();
}catch( IOException e ){
System.out.println(“Error!”);
}

// Display the name and age
System.out.println(“Hello ” + name +”!” + ” ” + “Your age is ” + age);

// Convert the String type of age variable into int primitive type variable ageint.
int ageint = Integer.parseInt(age);

// Now you can compare the int primitive type against int type value 100
if (ageint > 100){
System.out.println(“Hello ” + name +”!” + ” ” + “You are old.”);
} else{
System.out.println(“Hello ” + name +”!” + ” ” + “You are young.”);
}
}

}

Code-1.23: Modified GetInputFromKeyboard.java

5. Build and run the program

  • Right click MyGetInputFromKeyboardProject and select Run.
  • Observe that the program is expecting a user input.
  • Type in your name, Sang Shin, in this example and press Enter key.  Make sure you do not click Close Input.
  • Type in your age, 23, in this example and press Enter key.  Make sure you do not lock Close Input.
  • Observe that Hello <whatever name you entered>, in this example Hello Sang Shin is displayed in the Output window of the IDE.
  • Observe that Hello Sang Shin! You are young. is displayed.  (Figure-1.24 below)
Please Enter Your Name:
Sang Shin
Hello Sang Shin!
Please Enter Your Age:
23
Hello Sang Shin! Your age is 23
Hello Sang Shin! You are young.

Figure-1.24: Result of running the application

(1.3)  Display Javadoc in a context-senstive manner within NetBeans IDE

In this exercise, you are going to see the Javadoc of the Integer class in a context senstive fashion.  Before taking this step, please make sure you’ve download the Java Standard Development Kit (JDK™) version 6.0 Documentation zip file (download) into a directory of your choice.

1. Add J2SE Development Kit Documentation 6.0 zip file to the NetBeans.

  • Select Tools from top-level menu and select Java Platform. (Figure-1.31 below)


Figure-1.31: Open Java Platform Manager

  • Observe that the Java Platform Manager dialog box appears.
  • Click Javadoc tab.
  • Click Add ZIP/Folder. (Figure-1.32 below)


Figure-1.32: Add Javadoc file

  • Observe that the Add ZIP/Folder dialog box appears.
  • Browse down to the directory into which you have downloaded jdk-6-doc.zip.
  • Select jdk-6-doc.zip file and click Add ZIP/Folder. (Figure-1.33 below)


Figure-1.33:  Select jdk-6-doc.zip file

  • Observe that the jdk-6-doc.zip file is now shown under Platform Javadoc section. (Figure-1.34 below)
  • Click Close.


Figure-1.34: jdk-1_5_0-doc.zip file is added

2. Perform context-sensitive Javadoc.

  • Move the cursor over Integer string in the source editor of the NetBeans IDE.
  • Select Show Javadoc. (Figure-1.35 below)


Figure-1.35: Show Javadoc on Integer

  • Observe that the Javadoc of the Integer class gets displayed in the browser (Figure-1.36 below)


Figure-1.36: Javadoc of Integer class

  • Display context-sensitive Javadoc on String class.

Summary

In this exercise, you learned how to read data entered through a standard input device, keyboard.  You also learned how to use online version of Java documentation and how to display Javadoc of a class through context-senstive manner.

 

Exercise 2: Getting input from keyboard via JOptionPane

In this exercise, you are going to build the same application you built in Exercise 1 but this time using JOptionPane class.

  1. Build and run a Java program that uses conditional operators

(2.1) Build and run a Java program that uses conditional operators

1. Create a NetBeans project

  • Select File from top-level menu and select New Project.
  • Observe that the New Project dialog box appears.
  • Select Java under Categories section and Java Application under Projects section.
  • Click Next.
  • Under Name and Location pane, for the Project Name field, enter MyInputFromKeyboardJOptionPaneProject.
  • For the Create Main Class field, enter InputFromKeyboardJOptionPane.
  • Click Finish.
  • Observe that the MyInputFromKeyboardJOptionPaneProject project node is created under Projects pane of the NetBeans IDE and IDE generated InputFromKeyboardJOptionPane.java is displayed in the editor window of the IDE.
2. Modify the IDE generated InputFromKeyboardJOptionPane.java.
  • Modify the InputFromKeyboardJOptionPane.java as shown in Code-2.21 below. The code fragments that need to be added are highlighted in bold and blue-colored font.
import javax.swing.JOptionPane;
/*
* InputFromKeyboardJOptionPane.java
*
* Created on January 24, 2007, 10:46 AM
*
* To change this template, choose Tools | Template Manager
* and open the template in the editor.
*/

/**
*
* @author sang
*/
public class InputFromKeyboardJOptionPane {

/** Creates a new instance of InputFromKeyboardJOptionPane */
public InputFromKeyboardJOptionPane() {
}

/**
* @param args the command line arguments
*/
public static void main(String[] args) {
String name = “”;
name=JOptionPane.showInputDialog(“Please enter your name”);
String msg = “Hello ” + name + “!”;
JOptionPane.showMessageDialog(null, msg);
}

}

Code-2.21: Modified InputFromKeyboardJOptionPane.java

 

3. Build and run the program

  • Right click MyInputFromKeyboardJOptionPaneProject and select Run.
  • Observe that Input dialog box appears.
  • Enter your name, Sang Shin, in this example. (Figure-2.22 below)
  • Click OK.


Figure-2.22: Enter name

  • Observe that the message dialog box appears.


Figure-2.23: Message is displayed

Summary

In this exercise, you are going to build the same application you built in Exercise 1 but this time using JOptionPane class.

 

Homework exercise (for people who are taking Sang Shin’s “Java Programming online course”)

 

1. The homework is to modify the MyInputFromKeyboardJOptionPaneProject project above.   (You might want to create a new project by copying the MyGetInputFromKeyboardJOptionPaneProject project.)  You can name the new project in any way you want but here I am going to call to call it as MyGetInputFromKeyboardJOptionPaneProject2.
  • Make the program to ask the following question
    • Please enter your age
  • Display the entered age as following
    • If the age is over 100, display
      • Hello <name>, you are old!
    • Otherwise
      • Hello <name>, you are young!
2. Send the following files to javaprogramminghomework@sun.com with Subject as JavaIntro-javainputkey.
  • Zip file of the the MyGetInputFromKeyboardJOptionPaneProject2 NetBeans project.  (Someone else should be able to open and run it as a NetBeans project.)  You can use your favorite zip utility or you can use “jar” utility that comes with JDK as following.
    • cd <parent directory that contains MyGetInputFromKeyboardJOptionPaneProject2 directory> (assuming you named your project as MyGetInputFromKeyboardJOptionPaneProject2)
    • jar cvf MyGetInputFromKeyboardJOptionPaneProject2.zip MyGetInputFromKeyboardJOptionPaneProject2 (MyGetInputFromKeyboardJOptionPaneProject2 should contain nbproject directory)
  • Captured output screen  – name it as JavaIntro-javainputkey.gif orJavaIntro-javainputkey.jpg (or JavaIntro-javainputkey.<whatver graphics format>)
    • Any screen capture that shows that your program is working is good enough.  No cosmetic polishment is required.
  • If you decide to use different IDE other than NetBeans, the zip file should contain all the files that are needed for rebuilding the project.

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