Answer:
public static void classSplit(Scanner file){
    int studentsOf21 = 0, studentsOf22 = 0,studentsOf23 = 0, studentsOf24 = 0;
    while (file.hasNext() == true){
        String studentName = file.next();
        int year = file.nextInt();
        switch (year){
            case 2021: 
                studentsOf21++;
                break;
            case 2022: 
                studentsOf22++;
                break;
            case 2023: 
                studentsOf23++;
                break;
            case 2024: 
                studentsOf24++;
                break;
        }
    }
    int totalGraduate = studentsOf21+studentsOf22+studentsOf23+studentsOf24;
    System.out.printf("students in class of 2021: %.2f%n", students2021*100.0/totalGraduate);
    System.out.printf("students in class of 2022: %.2f%n", students2022*100.0/totalGraduate);
    System.out.printf("students in class of 2023: %.2f%n", students2023*100.0/totalGraduate);  
    System.out.printf("students in class of 2024: %.2f%n", students2024*100.0/totalGraduate);
}
Explanation:
The classSplit method of the java class accepts a scanner object, split the object by iterating over it to get the text (for names of students) and integer numbers (for graduation year). It does not need a return statement to ask it prints out the percentage of graduates from 2021 to 2024.