Java array: no value

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Java array: no value

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#1 by (3 votes)

1

I'm having a small problem regarding an array that I am trying to develop to get coordinates inside a JFrame and pass them to position the buttons correctly. Here is the code:

public class Coordenadas {

    //coordenadas
     int posicLinha;
     int posicColuna;
    //metodo para atribuir as coordenadas as devidas posições da matriz. 
    public void atribPosic (){
        Coordenadas[][] tabuleiro = new Coordenadas [8][8];//matriz de objetos coordenadas
        for (int l=0;l<8;l++){
            for (int c=0;c<8;c++){
                tabuleiro[l][c].posicLinha = 100+50*l;//primeira coordenada de linha, será igual a 100
                tabuleiro[l][c].posicColuna = 100+50*c;//primeira coordenada de coluna, será igual a 100
                System.out.print(tabuleiro[l][c].posicLinha);//imprime a coordenada da linha 
                System.out.print(tabuleiro[l][c].posicColuna);//imprime a coordenada da coluna
            }
        }
    }
    public static void main (String[]args){
        Coordenadas coordenadas = new Coordenadas ();
        coordenadas.atribPosic();
    }
}

My problem is that it does not print the value because of an error in the coordinate value assignment formula. I would like help, I do not know the cause of this error.

java matriz

asked by anonymous 19.11.2016 / 04:50

1 answer

selector does not work: $ ("div + p") Assign value to a variable in assembly 8086

score 3 · Answer 1

You do not say in the question what the error is. What you're having is NullPointerException . The assignment formulas you use are not the problem and are correct.

The reason for giving error is because the array is created initially containing null in all positions. And when you do tabuleiro[l][c].posicLinha , tabuleiro[l][c] will be null and try to access posicLinha null will NullPointerException .

The simplest and easiest solution to this problem is to add this at the beginning of% internal%:

tabuleiro[l][c] = new Coordenadas();

This will make your code run, but it still will not print what you want because you give for to a number, give another print soon then without adding space, nor line wrapping and nothing by making the numbers stick, and for each coordinate you do this by making all the numbers stick to each other forming a single digit language at the end in a single line with no spaces or commas and nothing in between. By using what is below, this is resolved:

System.out.println(tabuleiro[l][c].posicLinha + ", " + tabuleiro[l][c].posicColuna);

With these two fixes, your code will behave as expected. However, your code still suffers from other structural issues, although it works anyway (but will probably break if you make any changes). Note that to create the array you use an empty, useless instance of print that only exists so that you can call the Coordenadas method. This can be solved by using the atribPosic modifier in the method, thus dispensing with the need for an instance to use it.

Also, not putting visibility modifiers in your fields / attributes is not usually a good idea. You hardly intended to use package visibility. In addition, class names should preferably be nouns in the singular, and therefore static would be a better name than Coordenada .

There is also no need or purpose in "eating" some letters of variable names and methods, and therefore Coordenadas is better than atribuirPosicao . The same goes for atribPosic and posicLinha that could be posicColuna and posicaoLinha , but simply posicaoColuna and linha is simpler.

Your code with these fixes and changes all looks like this:

public class Coordenada {

    private int linha;
    private int coluna;

    public static void atribuirPosicao() {
        Coordenada[][] tabuleiro = new Coordenada[8][8];
        for (int l = 0; l < 8; l++) {
            for (int c = 0; c < 8; c++) {
                tabuleiro[l][c] = new Coordenada();
                tabuleiro[l][c].linha = 100 + 50 * l;
                tabuleiro[l][c].coluna = 100 + 50 * c;
                System.out.println(tabuleiro[l][c].linha + ", " + tabuleiro[l][c].coluna);
            }
        }
    }

    public static void main(String[] args) {
        Coordenada.atribuirPosicao();
    }
}

Finally, I recommend that you see this other answer of mine that I posted see another question to understand what causes a coluna .