public static void main(String[] args) {

	Grade guilherme = new Grade("guilherme", 7);

	Grade[] grades = {
		new Grade("Andre", 4),
		new Grade("Carlos", 8.5),
		new Grade("Ana", 10),
		new Grade("Jonas", 3),
		new Grade("Juliana", 6.7),
		new Grade("Lucia", 9.3),
		new Grade("Paulo", 9),
		new Grade("Mariana", 5),
		guilherme
	};

	sortByQuickSort(grades, 0, grades.length);

	for (Grade grade : grades) {
		System.out.println(grade.getStudent() + " grade: " + grade.getValue());
	}
}

private static void sortByQuickSort(Grade[] grades, int start, int end) {
	int elements = end - start;

	if (elements > 1) {
		int pivot = split(grades, start, end);
		sortByQuickSort(grades, start, pivot);
		sortByQuickSort(grades, pivot +1, end);
	}

}

private static int split(Grade[] grades, int start, int end) {
	Grade pivot = grades[end -1];
	int lesserThanPivot = 0;

	for (int checking = 0; checking < end -1; checking++) {
		Grade checkingGrade = grades[checking];

		if (checkingGrade.getValue() <= pivot.getValue()) {
			change(grades, checking, lesserThanPivot);
			lesserThanPivot++;
		}
	}

	change(grades, end -1, lesserThanPivot);

	return lesserThanPivot;
}

private static void change(Grade[] grades, int index1, int index2) {
	Grade grade1 = grades[index1];
	Grade grade2 = grades[index2];

	grades[index1] = grade2;
	grades[index2] = grade1;
}