Promedios clase

/*
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 */
package promedio;
/**
 *
 * @author BLACKANGEL
 */
public class Promedio {

    private String[] tareasLloyd={"90","97","75","92"}, pruebasLloyd={"88","40","94"},examenesLloyd={"75","90"};
    private String[] tareasAlice={"100","92","98","100"}, pruebasAlice={"82","83","91"},examenesAlice={"89","97"};
    private String[] tareasTyler={"0","87","7522"}, pruebasTyler={"0","75","78"}, examenesTyler={"100","100"};
    private String[][] Lloyd={{"Lloyd"}, tareasLloyd,pruebasLloyd,examenesLloyd};
    private String[][] Alice={{"Alice"},tareasAlice,pruebasAlice,examenesAlice};
    private String[][] Tylor={{"Tylor"}, tareasTyler,pruebasTyler,examenesTyler};
    private String[][][] estudiantes={Lloyd, Alice, Tylor};

    private void print(){
        for(int i=0; i<estudiantes.length; i++){
            System.out.println(estudiantes[i][0][0]+":");
            for(int j=1; j<estudiantes[i].length; j++){
                System.out.print("[");
                for(int k=0; k<estudiantes[i][j].length; k++){
                    if(k==estudiantes[i][j].length-1)
                        System.out.print(estudiantes[i][j][k]);
                    else
                        System.out.print(estudiantes[i][j][k]+", ");
                }
                System.out.print("]");
                System.out.println();
            }
        }
    }

    private static String promedio(String[] lista){
        double suma=0;
        int cont=0;
        double promedio=0;
        for(int i=0; i<lista.length; i++){
            suma+=Double.parseDouble(lista[i]);
            cont++;
        }
        promedio=suma/cont;
        return String.valueOf(promedio);
    }

    private String calcularPromedio(String[][] lista){
        double prom=0;
        for(int i=1; i<lista.length; i++){
            switch(i){
                case(1):
                    prom=Double.parseDouble(promedio(lista[i]))*0.1;
                    continue;
                case(2):
                    prom+=Double.parseDouble(promedio(lista[i]))*0.3;
                    continue;
                case(3):
                    prom+=Double.parseDouble(promedio(lista[i]))*0.6;
                    break;
            }
        }
        return String.valueOf(prom);
    }

    private String obtenerCalificaionenLetras(double nota){
        nota=Math.round(nota);
        if(nota>=90)
        return "A";
        if(nota>=80 & nota<90)
            return "B";
        if(nota>=70 & nota <80)
            return "C";
        if(nota>=60 & nota <70)
            return "D";
        if(nota<60)
            return "F";
        return " ";
    }

    private String calcularPromedioClase(String [][][] lista) {
        double promedio=0;
        int cont=0;
        double prom=0;
        for(int i=0; i<lista.length; i++){
            promedio+=Double.parseDouble(calcularPromedio(lista[i]));
            cont++;
        }
        prom=promedio/cont;
        return String.valueOf(prom);
    }

    public static void main(String[] args) {
        Promedio p1=new Promedio();
        System.out.println(p1.calcularPromedioClase(p1.estudiantes));
        System.out.println(p1.obtenerCalificaionenLetras(Double.parseDouble(p1.calcularPromedioClase(p1.estudiantes))));
    }
}