I'm doing an activity with the following statement:
You should implement a digital clock in Java. For this you should create three classes, namely: Counter, Clock and other class to test execution (Java application) with the name TestRelog. In Counter and Clock classes shall include the modifier methods and access methods for the created attributes. The result of your execution should display all possible clock times, example:
24 hour format
00:00 00:01 00:02 00:03 00:04 00:05 . . . 23:5912 hour format
12:00 a.m. 00:01 a.m. 00:02 a.m. . . . 11:54 p.m. 11:55 p.m. 11:56 p.m. 11:57 p.m. 11:58 p.m. 12:00 a.m.
There should be an option to display 12-hour or 24-hour time. If the selection is made to display in the 12 hour format, it should be displayed a.m. or p.m. as the case may be.
My classes are:
public class Contador {
private int contar;
//Metodo construtor
public void Contador(){
this.contar = 0;
}
//add 1
public void contar(){
this.contar = (contar +1 ) % 100;
}
//set
public void setContar(int num){
this.contar = num;
}
//get
public int getContar(){
return this.contar;
}
}//end of class
class clock
public class Relogio {
//Campos da classe
private Contador minutos;
private Contador horas;
//Constrio Objeto a partir da classe relogio relogio usando 2 objetos do tipo contador
public void Relogio(){
this.horas = new Contador();
this.minutos = new Contador();
}
//Metodos pra contar horas e minutos.
public void contarHoras(){
int limitar;
this.horas.contar();
limitar = horas.getContar();
limitar = ( limitar % 25 );
this.horas.setContar(limitar);
}
public void contarMinutos(){
int limitar;
this.minutos.contar();
limitar = minutos.getContar();
limitar = ( limitar % 61 );
this.minutos.setContar(limitar);
}
//Metodos get e set dos campos da classe:
public void setHoras(int hs){
this.horas.setContar( hs );
}//fim do SetHoras
public int getHoras(){
return this.horas.getContar();
}//fim do getHoras
public void setMinuto(int m){
this.minutos.setContar( m );
}//fim do SetMinuto
public int getMinutos(){
return this.minutos.getContar();
}//fim do getMinutos
//Metodos para printar em formato 12 hs ou em formato 24 hs
public void metodo12hs(){
int contador = 0;
while(contador < 24){
if(contador <= 12){
System.out.print(getHoras() + ":" + getMinutos() + "a.m");
}//end of if(contador <= 12)
else{
setHoras(1);//reiniciar o contador
System.out.print(getHoras() + ":" + getMinutos() + "p.m");
}//end of else
contador++;
contarHoras();
contarMinutos();
}//end of while(contador < 24)
}
public void metodo24hs(){
//metodo a ser implementado, quero fazer o metodo12hs funcionar primeiro
}
}//fim da Classe Relogio
Test class clock
import java.util.Scanner;
public class TesteRelogio {
public static void main(String[] args){
Scanner input = new Scanner(System.in);
Relogio rel = new Relogio();
int op;
while(true){
System.out.print("Formato de horas: ");
op = input.nextInt();
switch(op){
case 12: rel.metodo12hs(); break;
case 24: rel.metodo24hs(); break;
}//end of switch(op)
}//end of while(true)
//rel.metodo12hs();
}//end of main method
}//end of class
When compiling, after choosing the format 12 hs I get the following error message:
Exception in thread "main" java.lang.NullPointerException at Relogio.getHoras(Relogio.java:55) at Relogio.metodo12hs(Relogio.java:80) at TesteRelogio.main(TesteRelogio.java:22) /home/thiago/.cache/netbeans/8.1/executor-snippets/run.xml:53: Java returned: 1 BUILD FAILED (total time: 3 seconds)
I have tried to make changes and initialization of variables in the methods that appear in the error message but until now I have not found the problem.