Question

(This program is to be done on Java)

7.5 ArrayLists Part 1

A significant limitation of the array is you cannot add or delete elements from the array. The size is fixed and you can only do workarounds. An example is the following:

public class Ex_7_5_Prep
{
    public static void main(String[] args)
    {
        int[] intArray = { 5, 10, 15, 20 };

        printArray(intArray);

        intArray = addNewElement(intArray, 25);

        printArray(intArray);
    }

    public static int[] addNewElement(int[] originalArray, int newInt)
    {
        // Create new array one element larger than the original array
        int[] newArray = new int[originalArray.length+1];

        // Copy the data from the original array to the new array
        for ( int i = 0; i < originalArray.length; i++ )
        {
            newArray[i] = originalArray[i];
        }

        // Add the new element to the array
        newArray[newArray.length-1] = newInt;

        return newArray;
    }

    public static void printArray(int[] intArray)
    {
        for ( int i = 0; i < intArray.length; i++ )
        {
            System.out.print(intArray[i] + " ");
        }
        System.out.println();
    }
}

If the new array were created within the main() method, the program would experience an increase in memory usage that may not go away until the program ends. Once a variable is declared, it does not go away until the end of the scope. In the example above, we move from the main() method scope into the addNewElement() method scope to create the new array and copy the data. When we leave the addNewElement() method, everything within that scope is sent to the garbage collector for recovery of resources.

The approach mentioned above has been packaged into what is known as an ArrayList. The underlying code for an ArrayList is much more complex than the example above, but it essentially performs similar steps.

To delcare an ArrayList of Strings, you will use the following syntax:

ArrayList<String> countryNames = new ArrayList<>();

If you wanted to use integers, you would have to use the complex data type:

ArrayList<Integer> goldMedals = new ArrayList<>();

If you tried to use int instead of Integer, you would receive an error when compiling and IntelliJ would say you cannot use primitive data types. A complex data type is an enhanced version of your primitive data types but allows you to perform a variety of methods on the data.

Although you can have an ArrayList of ArrayLists create something similar to the multi-dimensional arrays, it would be better off to use classes, which is the example we will use here.

Within your main() method, add the following code:

ArrayList<OlympicTeam> olympicTeams = new ArrayList<>();

Create a new file named OlympicTeam.java along with the related class. Within the class you will have 4 variables: teamName, totalGoldMedals, totalSilverMedals, and totalBronzeMedals. Choose the appropriate data types, make the variables private, and create the related getter and setter methods.

Answer 1

Here is the code for the above assignment.

Feel free to comment on any doubt and give thumbs up!

Additionally, I have added comments to understand the code better.

There are 2 files that contain the code.

1. OlympicTeam.java which contains the OlympicTeam class with proper members variables and getters/setters method in it.

2. Main.java which contains the main method and ArrayList Object.

Code for OlympicTeam.java

class OlympicTeam {

private String teamName;

private int totalGoldMedals;

private int totalSilverMedals;

private int totalBronzeMedals;

public OlympicTeam(String teamName, int gold, int silver, int bronze) {

this.teamName = teamName;

totalGoldMedals = gold;

totalBronzeMedals = bronze;

totalSilverMedals = silver;

}

// Setters methods

void setTeamName(String name) {

teamName = name;

}

void setTotalGoldMedals(int gold) {

totalGoldMedals = gold;

}

void setTotalSilverMedals(int silver) {

totalSilverMedals = silver;

}

void setTotalBronzeMedals(int bronze) {

totalBronzeMedals = bronze;

}

// getters

String getTeamName() {

return teamName;

}

int getTotalGoldMedals() {

return totalGoldMedals;

}

int getTotalSilverMedals() {

return totalSilverMedals;

}

int getTotalBronzeMedals() {

return totalBronzeMedals;

}

}

Code for Main.java

import java.util.ArrayList;

public class Main

{

public static void main(String[] args) {

// creating ArrayList which consists of OlympicTeam objects

ArrayList<OlympicTeam> olympicTeams = new ArrayList<>();

// creating five objects of type OlympicTeam

OlympicTeam team1 = new OlympicTeam("Japan", 5, 6, 4);

OlympicTeam team2 = new OlympicTeam("America", 6, 2, 4);

OlympicTeam team3 = new OlympicTeam("India", 5, 7, 2);

OlympicTeam team4 = new OlympicTeam("China", 3, 6, 8);

OlympicTeam team5 = new OlympicTeam("Australia", 7, 9, 2);

// demonstration of getters and setters method

team1.setTotalBronzeMedals(8);

team1.setTotalGoldMedals(7);

team1.setTotalSilverMedals(5);

// adding all five objects in ArrayList

olympicTeams.add(team1);

olympicTeams.add(team2);

olympicTeams.add(team3);

olympicTeams.add(team4);

olympicTeams.add(team5);

// iterating over the olympicTeams to print information of each team using getters

for (OlympicTeam olympicTeam : olympicTeams) {

System.out.println("Team Name: " + olympicTeam.getTeamName() );

System.out.println("Number of Gold Medals: " + olympicTeam.getTotalGoldMedals());

System.out.println("Number of Silver Medals: " + olympicTeam.getTotalSilverMedals());

System.out.println("Number of Bronze Medals: " + olympicTeam.getTotalBronzeMedals());

System.out.println();

}

}

}

Screenshot of the test run

Thank You!