Reading 3D Ragged Arrays from a File

 1// Ragged3DReader.java
 2import java.io.File;
 3import java.io.FileNotFoundException;
 4import java.util.Scanner;
 5
 6public class Ragged3DReader {
 7    public static void main(String[] args) {
 8        // Department names for display (index 0=CS, 1=IT, 2=IS)
 9        String[] deptNames = {"CS", "IT", "IS"};
10
11        try {
12            // Create Scanner to read from file
13            Scanner fileReader = new Scanner(new File("departments.txt"));
14
15            // ============ STEP 1: Read number of departments ============
16            int numDepartments = Integer.parseInt(fileReader.nextLine().trim());
17
18            // ============ STEP 2: Read students per department ============
19            String studentsLine = fileReader.nextLine().trim();
20            String[] studentTokens = studentsLine.split("\\s+");
21
22            // Convert to int array: studentsPerDept[d] = number of students in dept d
23            int[] studentsPerDept = new int[numDepartments];
24            for (int d = 0; d < numDepartments; d++) {
25                studentsPerDept[d] = Integer.parseInt(studentTokens[d]);
26            }
27
28            // ============ STEP 3: Create 3D ragged array ============
29            // Only first dimension specified!
30            int[][][] marks = new int[numDepartments][][];
31
32            // ============ STEP 4 & 5: Read marks for each department and student ============
33            for (int d = 0; d < numDepartments; d++) {
34                // Create 2D array for this department's students
35                marks[d] = new int[studentsPerDept[d]][];
36
37                // For each student in this department
38                for (int s = 0; s < studentsPerDept[d]; s++) {
39                    // Read the line of course marks
40                    String line = fileReader.nextLine().trim();
41
42                    // Split by whitespace
43                    String[] tokens = line.split("\\s+");
44
45                    // Create array for this student's courses
46                    int[] courses = new int[tokens.length];
47
48                    // Convert each token to int
49                    for (int c = 0; c < tokens.length; c++) {
50                        courses[c] = Integer.parseInt(tokens[c]);
51                    }
52
53                    // Assign to the 3D array
54                    marks[d][s] = courses;
55                }
56            }
57
58            // Close the file
59            fileReader.close();
60
61            // ============ PRINT THE 3D RAGGED ARRAY ============
62            System.out.println("3D Ragged Array of Department Marks:");
63            System.out.println("====================================");
64
65            for (int d = 0; d < marks.length; d++) {
66                System.out.println("\nDepartment " + d + " (" + deptNames[d] + "):");
67
68                for (int s = 0; s < marks[d].length; s++) {
69                    System.out.print("  Student " + s + ": ");
70
71                    for (int mark : marks[d][s]) {
72                        System.out.print(mark + " ");
73                    }
74                    System.out.println("(" + marks[d][s].length + " courses)");
75                }
76            }
77
78        } catch (FileNotFoundException e) {
79            System.err.println("File not found: " + e.getMessage());
80        }
81    }
82}

3D Ragged Array of Department Marks:
====================================

Department 0 (CS):
  Student 0: 85 90 78 (3 courses)
  Student 1: 90 85 88 92 (4 courses)

Department 1 (IT):
  Student 0: 75 80 (2 courses)
  Student 1: 88 92 85 90 78 (5 courses)
  Student 2: 70 75 80 (3 courses)

Department 2 (IS):
  Student 0: 95 88 92 (3 courses)
  Student 1: 80 85 (2 courses)