Question

all
I am interesting learning how to achieve a 2d String [][] array console printout using only native, pure java. The following code prints out a 2d matrix when I run my program, but one particular line was confusing while doing some test runs on converting my string to a 2d array:

rulesTable[i][j] = rulesMatrix[j];

Is there a way I could code this wherein rulesMatrix would be = to a 2d String array instead of the 1d String array I currently have? Any tips would be great. Thank you. The following snippet contains the loop-in-question:

protected void forgeGrammar()
{

    //this verifies that all 5 rules displayed in the console are valid
    grammarRules = new String(startingRule + secondRule + thirdRule + fourthRule + fifthRule);

    rulesArray = new String[grammarRules.length()];

    //remove the commas from the grammar  
    rulesArray = grammarRules.split("[,]");

    //convert the grammar to a 2D String array
    rulesTable = new String[rulesArray.length][5];
    for (int i = 0; i < rulesTable.length; i++)
    {
        String[] rulesMatrix = rulesArray[i].split(blank);

        for(int j = 0; j < rulesMatrix.length; j++)
        {
            rulesTable[i][j] = rulesMatrix[j];
        }
    }

Answer 1

In your code rulesTable Never gets initialized that’s why NullPointer exception is thrown at below line

rulesTable[0][0].contains(rules_input.substring(0, 4));