Question

I am writing a program that will enter an array of Students with their name and gpa’s and return only the failing students. I am unsure how to return an array that will avoid returning null as an element of that array. I.e. if there are 4 students in the initial array, but only 2 are failing, my array is returning: student1, student2, null, null.

Student Jim = new Student("Jim",1.4);
    Student Tom = new Student("Tom",3.0);
    Student John = new Student("John",4.0);
    Student Bill = new Student("Bill",1.2);
    Student[] group1 = {Jim,Tom,John,Bill};

public Student[] getFailing(Student[] students) {
    int i, j;
    Student[] failing = new Student[students.length];
    Student temp;
    for(i=0, j=0; i< students.length; i++){
            if(students[i].getGpa() < 2.0){
                temp = students[i];
                failing[j] = temp;
                j++;
            }

    }
    return failing;
}

My current result when I do a test run in main is:

name = Jim gpa = 1.4
name = Bill gpa = 1.2
null
null

Answer 1

If the only problem is printing the nulls, i.e. it’s OK if your array has null values but you don’t want to see them in your output, then you can leave your method as it is and change your printing code so that it checks for null, and avoid printing them.

But if you must keep null values out of your array, you can use a dynamically resizing data structure like ArrayList, and get an array out of it using the toArray method.

Without using ArrayList, since you’re tracking how many Student objects represent failing students with the j variable, after you collect the failing student objects you could create a new array of the desired length, and then fill it with only the non-null students using a loop, or using Arrays.copyOf, or System.arraycopy.