Array out of bounds - Basic Java

Array out of bounds - Basic Java

I'm learning how to program in Java but I can't seem to get past an array
problem. See, I get an array out of bounds error when I run this program:
I know this is probably really easy to solve but I have no idea what's
going on.
Thanks!
public class AlturaPromedio {
float alturas[];
int cont;
float promedio;
InputStreamReader inputStream = new InputStreamReader(System.in);
BufferedReader buffRead = new BufferedReader(inputStream);
float cargarAlturas() throws IOException {
alturas = new float[4];
for (cont = 0; cont < alturas.length; cont++) {
System.out.println("Escriba el nombre de la primer altura:");
alturas[cont] = Float.parseFloat(buffRead.readLine());
}
return alturas[cont];
}
float calcularPromedio() {
promedio = (alturas[1] + alturas[2] + alturas[3] + alturas[4] +
alturas[0]) / 5;
return promedio;
}
/*float calcularMaximo(){
maximo = Alturas.min(alturas);
*/
public static void main(String[] ar) throws IOException {
AlturaPromedio personas = new AlturaPromedio();
personas.cargarAlturas();
personas.calcularPromedio();
}
}