Java Controls

Expected duration: 90 minutes

Exercise 1: if/else control structure

In this exercise,  you will learn how to write a Java program that uses if/else control structure.

1. Build and run a Java program that uses if/else control structure
   
2. Build and run 2nd Java program that uses if/else control structure
   

(1.1) Build and run a Java program that uses if/else control structure

1.  Open MyGradesProject NetBeans project. 

• Select File->Open Project (Ctrl+Shift+O). The Open Project dialog box appears.
• Browse down to <LAB_UNZIPPED_DIRECTORY>/javacontrol/samples directory. 
  
• Windows: If you unzipped the hands-on lab zip file, 1034_javacontrol.zip, under C:\ directory, the directory to which you want to browse down should be C:\javacontrol\samples.
• Solaris/Linux: If you unzipped the 1034_javacontrol.zip file under $HOME directory, the directory to which you want to browse down should be $HOME/javacontrol/samples.
• Select MyGradesProject.
• Click Open Project. (Figure-1.10 below)  

Figure-1.10: Open MyGradesProject

2. Study the Grades.java which uses if/else control structure,

• Expand MyGradesProject->Source Packages.
• Double click Grades.java to open it in the editor window.
• Study how if/else control structure is used, whose code fragment is highlighted in bold font in Code-1.11 below.
  

import javax.swing.JOptionPane; public class Grades {         public static void main(String[] args) {                 int mathGrade = 0;         int historyGrade = 0;         int scienceGrade = 0;         double average = 0;                 mathGrade = Integer.parseInt(JOptionPane.showInputDialog("Enter math grade between 0 and 100!"));         historyGrade = Integer.parseInt(JOptionPane.showInputDialog("Enter history grade between 0 and 100!"));         scienceGrade = Integer.parseInt(JOptionPane.showInputDialog("Enter science grade between 0 and 100!"));                 // Compute average         average = (mathGrade+historyGrade+scienceGrade)/3;                 // Perform if & else control         if (average >= 60){             JOptionPane.showMessageDialog(null, "Good job! Your average is " + average);         } else{             JOptionPane.showMessageDialog(null, "You need to do better! Your average is " + average);         }             } }

Code-1.11: Grades.java

3. Build and run the program

• Right click MyGradesProject and select Run Project.
• Enter math, history, and science grades and see the result. (Figure-1.12, Figure-1.13, Figure-1.14, Figure-1.15 below)
  

Figure-1.12: Enter math grade dialog box


Figure-1.13: Enter history grade dialog box


Figure-1.14: Enter science grade dialog box


Figure-1.15: Computing average and display different message using if/else


4. (For your own exercise - this is not a homework) Modify the Grades.java as following:

• If the average is greater than 90 (average > 90), display "You worked too hard! Your average is xx.0."
• If the average is greater than 50 (average > 50) and less than or equal  to 90 (average <= 90), display "You did OK! Your average is xx.0."
• If the average is less than or equal to 50 (average <= 50), display "You need to do some work! Your average is xx.0."

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(1.2) Build and run another Java program that uses if/else control structure

1.  Open MyNumWordsProject NetBeans project. 

Figure-1.22: Enter a number

Figure-1.23: Display string equivalent of the number entered

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Summary

In this exercise, you learned how to if/else control structure of the Java programming language.
   
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Exercise 2: for loop

In this exercise, you will learn how to write a Java program that uses for loop.

1. Build and run a Java program that uses for loop
   

(2.1) Build and run a Java program that uses a for loop

1.  Open MyForLoopProject NetBeans project. 

import javax.swing.JOptionPane; public class ForLoop {         /** Creates a new instance of ForLoop */     public ForLoop() {     }         /**      * @param args the command line arguments      */     public static void main(String[] args) {         // Declare and initialize String array variable called names.         String names []={"Beah","Bianca","Lance","Belle","Nico","Yza","Gem","Ethan"};                 // This is the search string we are going to use to search the array.         String searchName = JOptionPane.showInputDialog("Enter either \"Yza\" or \"noname\"!");                 // Declare and initialize boolean primitive type variable called foundName.         boolean foundName =false;                 // Search the String array using for loop.         //  * The "names.length" is the size of the array.         //  * This for loop compares the value of each entry of the array with         //     the value of searchString String type variable.         //  * The equals(..) is a method of String class. Think about why you         //     cannot use "names[i] == searchName" as comparison logic here.         for (int i=0; i<names.length; i++){             if (names [i ].equals(searchName)){                 foundName =true;                 break;             }         }                 // Display the result         if (foundName)             JOptionPane.showMessageDialog(null, searchName + " is found!");         else             JOptionPane.showMessageDialog(null, searchName + " is not found!");             }     }

Code-2.21: ForLoop.java

3. Build and run the program

• Right click MyForLoopProject and select Run Project.
• Enter Yza which is one of the strings that are stored in the array. (Figure-2.22 below)
• Observe that the Yza is found through the for loop based search. (Figure-2.23 below)
  

Figure-2.22: Enter search string


Figure-2.23: Yza is found

• Right click MyForLoopProject and select Run Project.
• Enter noname which is not one of the strings that are stored in the array. (Figure-2.24 below)
• Observe that the noname is not found through the for loop based search. (Figure-2.25 below)

Figure-2.24: Enter search string


Figure-2.25: noname is not found

Summary

In this exercise, you learned how to use a for loop.

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Exercise 3: while loop

In this exercise, you will learn how to write Java programs that use while and do-while loop.

1. Build and run a Java program that uses while loop
2. Build and run a Java program that uses do-while loop

(3.1) Build and run a Java program that uses a while loop

1.  Open MyFiveNamesUsingwhileProject NetBeans project. 

import java.io.BufferedReader; import java.io.InputStreamReader; public class FiveNamesUsingwhile {         /**      * Creates a new instance of FiveNamesUsingwhile      */     public FiveNamesUsingwhile() {     }         /**      * @param args the command line arguments      */     public static void main(String[] args) {         BufferedReader reader                 = new BufferedReader(new InputStreamReader(System.in));         String name = "";         int counter = 0;                 //gets the users' name         try{             System.out.println("Enter name: ");             name = reader.readLine();         }catch(Exception e){             System.out.println("Invalid input");             System.exit(0);         }                 // while loop that prints the name five times         while (counter < 5){             System.out.println(name);             counter++;         }     } }

Code-3.11: FiveNamesUsingwhile.java

3. Build and run the program

• Right click MyFiveNamesUsingwhileProject and select Run Project.
• Observe that the program prompts you to enter your name.
• Enter your name in the Input field and press Enter key.  (Figure-3.12 below) (Do not press Close Input.)
  

Figure-3.12: Enter your name

• Observe that the name is repeatedly displayed 5 times. (Figure-3.13 below) You will see 6 names, the first of which is input that is redisplayed.)
  

Figure-3.13: Name is repeated 5 times using while loop

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(3.2) Build and run a Java program that uses a do-while loop

1.  Open MyFiveNamesUsingdowhileProject NetBeans project. 

Summary

In this exercise, you learned how to use while and do-while loop.

Homework exercise (for people who are taking Sang Shin's "Java Programming online course")

• Instead of using for loop, use while loop.
  

• Zip file of the the MyOwnWhileProject 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 MyOwnWhileProject directory> (assuming you named your project as MyOwnWhileProject)
  
• jar cvf MyOwnWhileProject.zip MyOwnWhileProject (MyOwnWhileProject should contain nbproject directory)
• Captured output screen  - name it as JavaIntro-javacontrol.gif orJavaIntro-javacontrol.jpg (or JavaIntro-javacontrol.<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 - war file with necessary source files is OK.