토요일, 12월 21
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#005 Java Controls

by nobaksan

 

Lab Exercises

 

Exercise 1: if/else control structure

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

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

1.  Open MyGradesProject NetBeans project.

  • Select File->Open Project (Ctrl+Shift+O).

  • Observe 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

  • Observe that the MyGradesProject project node is displayed under Projects pane of the NetBeans IDE.
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.
  • 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.”

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

1.  Open MyNumWordsProject NetBeans project.

  • Select File->Open Project (Ctrl+Shift+O). The Open Project dialog box appears.
  • Browse down to <LAB_UNZIPPED_DIRECTORY>/javacontrol/samples directory.
  • Select MyNumWordsProject.
  • Click Open Project.
  • Observe that the MyNumWordsProject project node is displayed under Projects pane of the NetBeans IDE.

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

  • Expand MyNumWordsProject->Source Packages.
  • Double click NumWords.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-1.21 below.
import javax.swing.JOptionPane;

public class NumWords {

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

/**
* @param args the command line arguments
*/
public static void main(String[] args) {
String msg = “”;
int input = 0;

// Get the input string
input = Integer.parseInt(JOptionPane.showInputDialog
(“Enter number between 1 to 10”));

// Set msg variable to the string equivalent of input
if(input == 1)        msg = “one”;
else if(input == 2)    msg = “two”;
else if(input == 3)    msg = “three”;
else if(input == 4)    msg = “four”;
else if(input == 5)    msg = “five”;
else if(input == 6)    msg = “six”;
else if(input == 7)    msg = “seven”;
else if(input == 8)    msg = “eight”;
else if(input == 9)    msg = “nine”;
else if(input == 10)    msg = “ten”;
else            msg = “Invalid number”;

// Display the number in words if with in range
JOptionPane.showMessageDialog(null,msg);
}
}

Code-1.21: NumWords.java

3. Build and run the program

  • Right click MyNumWordsProject and select Run.
  • Enter a number and click OK. (Figure-1.22 below)

Figure-1.22: Enter a number

Figure-1.23: Display string equivalent of the number entered

Summary

In this exercise, you learned how to if/else control structure of the Java programming language.

 

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.

  • Select File->Open Project (Ctrl+Shift+O). The Open Project dialog box appears.
  • Browse down to <LAB_UNZIPPED_DIRECTORY>/javacontrol/samples directory.
  • Select MyForLoopProject.
  • Click Open Project.
  • Observe that the MyForLoopProject project node is displayed under Projects pane of the NetBeans IDE.
2. Study the ForLoop.java which uses if/else control structure,
  • Expand MyForLoopProject->Source Packages.
  • Double click ForLoop.java to open it in the editor window.
  • Study how for loop control structure is used, whose code fragment is highlighted in bold font in Code-2.21 below.
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.
  • 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.
  • 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.

 

 

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.

  • Select File->Open Project (Ctrl+Shift+O). The Open Project dialog box appears.
  • Browse down to <LAB_UNZIPPED_DIRECTORY>/javacontrol/samples directory.
  • Select MyFiveNamesUsingwhileProject.
  • Click Open Project.
  • Observe that the MyFiveNamesUsingwhileProject project node is displayed under Projects pane of the NetBeans IDE.
2. Study the FiveNamesUsingwhile.java which uses if/else control structure,
  • Expand MyFiveNamesUsingwhileProject->Source Packages.
  • Double click FiveNamesUsingwhile.java to open it in the editor window.
  • Study how for loop control structure is used, whose code fragment is highlighted in bold font in Code-3.11 below.
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.
  • 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

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

1.  Open MyFiveNamesUsingdowhileProject NetBeans project.

  • Select File->Open Project (Ctrl+Shift+O). The Open Project dialog box appears.
  • Browse down to <LAB_UNZIPPED_DIRECTORY>/javacontrol/samples directory.
  • Select MyFiveNamesUsingdowhileProject.
  • Click Open Project.
  • Observe that the MyFiveNamesUsingdowhileProject project node is displayed under Projects pane of the NetBeans IDE.
2. Study the FiveNamesUsingdowhile.java which uses if/else control structure,
  • Expand MyFiveNamesUsingdowhileProject->Source Packages.
  • Double click FiveNamesUsingdowhile.java to open it in the editor window.
  • Study how for loop control structure is used, whose code fragment is highlighted in bold font in Code-3.21 below.
import java.io.BufferedReader;
import java.io.InputStreamReader;

public class FiveNamesUsingdowhile {

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);
}

// Use do-while loop that prints the name five times
do{
System.out.println(name);
counter++;
}while(counter < 5);
}

}

Code-3.21: FiveNamesUsingdowhile.java

3. Build and run the program

  • Right click MyFiveNamesUsingdowhileProject and select Run.
  • Observe that the program prompts you to enter your name.
  • Enter your name in the Input field and press Enter key.  (Do not press Close Input.)
  • Observe that the name is repeatedly displayed 6 times.

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”)

 

1. The homework is to modify the MyForLoopProject project (Exercise 2 above) described below.   (You might want to create a new project by copying the MyForLoopProject project.)  You can name the new project in any way you want but here I am going to call to call it as MyOwnWhileProject.
  • Instead of using for loop, use while loop.
2. Send the following files to javaprogramminghomework@sun.com with Subject as JavaIntro-javacontrol.
  • 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.

 

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