Found Bug but can't understand it

[onemanclapping]

hi,

I have to do a program that generates 'n' different combinations of 7 different numbers between 1 and 49, so I did this:

import java.util.*;
public class Totoloto {
	
	public static void main(String[] args) {
		System.out.print("Quantas apostas?");
		Scanner s = new Scanner(System.in);
		int n=s.nextInt();
		int[][] apostas = geraApostas(n);
		for(int i=0;i<apostas.length;i++)
		{
			System.out.print("[");
			for(int a=0;a<7;a++)
			{
				System.out.print(apostas[i][a]);
				if(a!=6)
					System.out.print(", ");
			}
			System.out.println("]");
		}
	}
	
	private static int[] geraAposta(){
		int[] aposta = new int[7];
		for(int i=0;i<7;i++)
		{
			int num;
			Boolean existe;
			do{
				existe=false;
				num=(int) (Math.random()*49+1);
				for(int a=0;a<7;a++)
					if(aposta[a]==num)
						existe=true;
			}while(existe);
			aposta[i]=num;				
		}
		return aposta;		
	}

	private static int[][] geraApostas(int n){
		int[][] apostas = new int[7][n];
		System.out.println(n + "" + apostas.length);
		for(int i=0;i<n;i++)
		{
			int[] aposta;
			Boolean existe;
			do{
				existe=false;
				aposta=geraAposta();
				for(int a=0;a<n;a++)
					if(apostas[n]==aposta)
						existe=true;
			}while(existe);
			apostas[i]=aposta;
		}
		return apostas;
	}
}

When I run it:

Quantas apostas?9
97
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 9
	at Totoloto.geraApostas(Totoloto.java:54)
	at Totoloto.main(Totoloto.java:12)

This happens cecause, for int[][] apostas = new int[7][n];, apostas.lenght equals 7! how can I obtain 'n' with just the array and the length function?

thanks in advance!

[Ezzaral]

You are very close there: int[][] apostas = new int[n][7];
You want 'n' elements that each contain an array of 7 elements. Your outer loop for(int i=0;i<n;i++) then denotes that first dimension, so aposta[i]=geraAposta();

[onemanclapping]

You are very close there: int[][] apostas = new int[n][7]; You want 'n' elements that each contain an array of 7 elements. Your outer loop for(int i=0;i<n;i++) then denotes that first dimension, so aposta[i]=geraAposta();

thank you very much! problem solved.