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#006 Java Array

by nobaksan

Lab Exercises

 

Exercise 1: Build and run Java programs that use Java array of int

In this exercise, you are going to build  simple Java applications that use  array  of int.

  1. Build and run a Java program that uses single-dimensional array of int
  2. Build and run a Java program that uses two-dimensional array of int
  3. Build and run a Java program that computes the greatest number 

(1.1) Build and run a Java program that uses single-demensional array of int

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 MyJavaArrayProject.
  • For the Create Main Class field, enter JavaArray. (Figure-1.10 below)
  • Click Finish.


Figure-1.10: Create a new NetBeans project

  • Observe that the MyJavaArrayProject project node is created under Projects pane of the NetBeans IDE and IDE generated JavaArray.java is displayed in the editor window of the IDE.
2. Modify the IDE generated JavaArray.java.
  • Modify the JavaArray.java as shown in Code-1.11 below.
public class JavaArray {

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

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

// Declare and create int array whose size is 10
int[] ages = new int[10];

// Display the value of each entry in the array
for( int i=0; i<ages.length; i++ ){
System.out.print( ages[i] );
}
}

}

Code-1.11: Modified JavaArray.java

3. Build and run the program

  • Right click MyJavaArrayProject and select Run.
  • Observe the result in the Output window.  (Figure-1.12 below)
0 0 0 0 0 0 0 0 0 0

Figure-1.12: Result

 

4. (For your own exercise) Modify JavaArray.java as following, build and run the program.

  • Just before the for loop that prints out the value of each entry of the ages[] array, create another for loop in which a value of 100 is assigned to the first entry of the array, ages[0], 101 to the next entry of the array, ages[1], and so on.

(1.2) Build and run a Java program that uses two-dimensional array of int

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 MyJavaTwoDimensionArrayProject.
  • For the Create Main Class field, enter JavaTwoDimensionArray. (Figure-1.10 below)
  • Click Finish.
  • Observe that the MyJavaTwoDimensionArrayProject project node is created under Projects pane of the NetBeans IDE and IDE generated JavaTwoDimensionArray.java is displayed in the editor window of the IDE.
2. Modify the IDE generated JavaTwoDimensionArray.java.
  • Modify the JavaTwoDimensionArray.java as shown in Code-1.11 below.
public class JavaTwoDimensionArray {

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

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

// Declare and create two dimensional int array whose size is 10 by 5
int[][] ages = new int[10][5];

// Display the number of rows and columns
System.out.println(“ages.length = ” + ages.length);
System.out.println(“ages[1].length = ” + ages[1].length);

// Display the value of each entry in the array
for( int i=0; i<ages.length; i++ ){
System.out.println(“\nStarting row ” + i);
for( int j=0; j<ages[i].length; j++ ){
ages[i][j] = i * j;
System.out.print( ages[i][j] + ” ” );
}
}
}
}

Code-1.11: Modified JavaTwoDimensionArray.java

3. Build and run the program

  • Right click MyJavaTwoDimensionArrayProject and select Run.
  • Observe the result in the Output window.  (Figure-1.12 below)
ages.length = 10
ages[1].length = 5

Starting row 0
0 0 0 0 0
Starting row 1
0 1 2 3 4
Starting row 2
0 2 4 6 8
Starting row 3
0 3 6 9 12
Starting row 4
0 4 8 12 16
Starting row 5
0 5 10 15 20
Starting row 6
0 6 12 18 24
Starting row 7
0 7 14 21 28
Starting row 8
0 8 16 24 32
Starting row 9
0 9 18 27 36

Figure-1.12: Result

4. (For your own exercise) Create a NetBeans project as following.  Build and run the program.

  • Declare and initialize 3-dimensional array of int
  • Initialize each cell with increasing integer number starting from 1000, 1001, 1002, and so on.

(1.3) Build and run a Java program that finds the greatest number

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 MyGreatestNumberProject.
  • For the Create Main Class field, enter GreatestNumber. (Figure-1.10 below)
  • Click Finish.
  • Observe that the MyGreatestNumberProject project node is created under Projects pane of the NetBeans IDE and IDE generated GreatestNumber.java is displayed in the editor window of the IDE.
2. Modify the IDE generated GreatestNumber.java.
  • Modify the GreatestNumber.java as shown in Code-1.11 below.
import javax.swing.JOptionPane;

public class GreatestNumber {

public static void main(String[] args) {
int[] num = new int[10];
int counter;
int max = 0;
int totalnumber = 3;

// Prompt a user to enter numbers
for(counter = 0; counter < totalnumber; counter++){

num[counter] = Integer.parseInt
(JOptionPane.showInputDialog(“Enter numbers until ” + totalnumber + ” numbers are entered”));

// Compute the greatest number up to this point
if((counter == 0)||(num[counter] > max))
max = num[counter];
}

// Display the greatest number.
JOptionPane.showMessageDialog(null,”The number with the greatest value is ” + max);
}

}

Code-1.11: Modified GreatestNumber.java

3. Build and run the program

  • Right click MyGreatestNumberProject and select Run.
  • Enter 3 numbers.
  • Observe that the greatest number is displayed.
4. (For your own exercise) Modify MyGreatestNumberProject as following:

  • Compute the smallest number and display it.

Summary

In this exercise, you learned how to use Java array.

 

Exercise 2: Build and run Java programs that use Java array of String

In this exercise, you are going to build  simple Java applications that use  array  of String.

  1. Build and run a Java program that uses single-dimentional array of String

(2.1) Build and run a 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 MyDaysOfTheWeekProject.
  • For the Create Main Class field, enter DaysOfTheWeek.
  • Click Finish.
2. Modify the IDE generated DaysOfTheWeek.java.
  • Modify the DaysOfTheWeek.java as shown in Code-2.11 below.
public class DaysOfTheWeek {

public static void main(String[] args) {

// Declare and initialize String array of the days of the week
String[] days = {“Sunday”,”Monday”,”Tuesday”,”Wednesday”,
“Thursday”,”Friday”,”Saturday”};

// Display days of the week using while loop
System.out.println(“Display days of week using while loop”);
int counter = 0;
while(counter < days.length){
System.out.println(days[counter]);
counter++;
}

// Display days of the week using do-while loop
System.out.println(“Display days of week using do-while loop”);
counter = 0;
do{
System.out.println(days[counter]);
counter++;
} while(counter < days.length);

// Display days of the week using for loop
System.out.println(“Display days of week using for loop”);
for(counter = 0; counter < days.length; counter++){
System.out.println(days[counter]);
}

}

}

Code-2.11: Modified DaysOfTheWeek.java

3. Build and run the program

  • Right click MyDaysOfTheWeekProject and select Run.
  • Observe that the days of the week are displayed 3 times.  (Figure-2.12 below)
Display days of week using while loop
Sunday
Monday
Tuesday
Wednesday
Thursday
Friday
Saturday
Display days of week using do-while loop
Sunday
Monday
Tuesday
Wednesday
Thursday
Friday
Saturday
Display days of week using for loop
Sunday
Monday
Tuesday
Wednesday
Thursday
Friday
Saturday

Figure-2.12: Result

 

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

 

1. The homework is to create the MyOwnJavaArrayProject project as following:
  • Ask the English version of the full names (first-name last-name) of three of your family members using showInputDialog() method of the JOptionPane class.
  • Display the name of the family member who has the longest first name (not the longest of the  total name) as following.  (If there is a tie, just display one of the two.)
    • Daniel Shin has the longest first name
Hint: You will have use various methods of String class.  The following is an example code fragment you might be able to use.  Please feel free to use alternative ways of doing the homework.

// Get the first name from a name string using split() instance (non-static) method
String[] nameArrayForPerson1 = person1NameInstance.split(” “);
String[] nameArrayForPerson2 = person2NameInstance.split(” “);

// Get the lengths of strings using length() instance (non-static) method
int lengthOfFirstNameOfPerson1 = nameArrayForPerson1[0].length();
int lengthOfFirstNameOfPerson2 = nameArrayForPerson2[0].length();

// Compare the lengths of the first names between person1 and person2
if (lengthOfFirstNameOfPerson1 > lengthOfFirstNameOfPerson2){
System.out.println(nameArrayForPerson1[0] +
” has longer first name than ” +
nameArrayForPerson2[0]);
}
2. Send the following files to javaprogramminghomework@sun.com with Subject as JavaIntro-javaarray.
  • Zip file of the the MyOwnJavaArrayProject 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 MyOwnJavaArray directory> (assuming you named your project as MyOwnJavaArrayProject)
    • jar cvf MyOwnJavaArrayProject.zip MyOwnJavaArrayProject (MyOwnJavaArrayProject should contain nbproject directory)
  • Captured output screen  – name it as JavaIntro-javaarray.gif orJavaIntro-javaarray.jpg (or JavaIntro-javaarray.<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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