Understanding Jagged Array in Java

int twoD[][] = new int[4][];
twoD[0] = new int[1];
twoD[1] = new int[2];
twoD[2] = new int[3];
twoD[3] = new int[4];

public class JaggedArrayExample {

    public static void main(String[] args) {
        // Declare a jagged array with 3 rows
        int[][] jaggedArray = new int[3][];

        // Initialize the inner arrays with different lengths
        jaggedArray[0] = new int[] { 1, 2, 3 };
        jaggedArray[1] = new int[] { 4, 5 };
        jaggedArray[2] = new int[] { 6, 7, 8, 9 };

        // Access and print the elements of the jagged array
        System.out.println("Jagged Array Elements:");
        for (int i = 0; i < jaggedArray.length; i++) {
            for (int j = 0; j < jaggedArray[i].length; j++) {
                System.out.print(jaggedArray[i][j] + " ");
            }
            System.out.println(); // Move to the next line after each row
        }

        //Another way to initialize a jagged array.
        int[][] anotherJaggedArray = {
                {10,11},
                {12,13,14,15},
                {16}
        };

        System.out.println("Another Jagged Array Elements:");
        for (int i = 0; i < anotherJaggedArray.length; i++) {
            for (int j = 0; j < anotherJaggedArray[i].length; j++) {
                System.out.print(anotherJaggedArray[i][j] + " ");
            }
            System.out.println();
        }
    }
}

Jagged Array Elements:
1 2 3 
4 5 
6 7 8 9 
Another Jagged Array Elements:
10 11 
12 13 14 15 
16 

public class WeeklyHours {
    public static void main(String[] args) {
        // Creating a jagged array for hours 
        // worked on different days of the week
        double[][] weekHours = {
            {8.5}, // Monday
            {8.0, 3.5}, // Tuesday (two shifts)
            {8.0}, // Wednesday
            {8.0, 4.0}, // Thursday (two shifts)
            {6.5}, // Friday
            {}, // Saturday (no work)
            {} // Sunday (no work)
        };
 
        // Displaying hours
        String[] days = {"Monday", "Tuesday", "Wednesday", 
                "Thursday", "Friday", "Saturday", "Sunday"};
        for (int i = 0; i < weekHours.length; i++) {
            System.out.print(days[i] + ": ");
            for (double hours : weekHours[i]) {
                System.out.print(hours + " ");
            }
            System.out.println();
        }
    }
}

Monday: 8.5 
Tuesday: 8.0 3.5 
Wednesday: 8.0 
Thursday: 8.0 4.0 
Friday: 6.5 
Saturday: 
Sunday: 

public class StudentGrades {
    public static void main(String[] args) {
        // Grades for three subjects, each having 
        // a different number of assessments
        int[][] grades = {
            {87, 92}, // Grades in Subject 1 (e.g., Math)
            {78, 85, 90}, // Grades in Subject 2 (e.g., Science)
            {85, 80} // Grades in Subject 3 (e.g., History)
        };
 
        // Subject names
        String[] subjects = {"Math", "Science", "History"};
 
        // Displaying grades for each subject
        for (int i = 0; i < grades.length; i++) {
            System.out.print(subjects[i] + " Grades: ");
            for (int grade : grades[i]) {
                System.out.print(grade + " ");
            }
            System.out.println();
        }
    }
}

Math Grades: 87 92 
Science Grades: 78 85 90 
History Grades: 85 80