1

I have almost managed to get my program working, but there is still one last bit I am having trouble with. I do not believe anybody has asked this question yet, because I am trying to select a JButton according to an array value which has been randomly selected. I generated one hundred JButtons on a grid, and I want to randomly select twenty for changing their text. Problem is, the text is not changing! So I am thinking I have not really selected any buttons. My problem code is as follows:

for (int i = 0; i < 20; i++)
{
    Random randomRow = new Random(10);
    Random randomColumn = new Random(10);
    if (button == buttons[randomRow.nextInt(10)+1][randomColumn.nextInt(10)+1])
    {
        button.setText("treasure");
    }
}
Ari Seyhun
  • 11,506
  • 16
  • 62
  • 109
Orion
  • 13
  • 2
  • Your attempt at selecting 20 buttons is not correct. – Ari Seyhun Dec 10 '17 at 23:23
  • 1
    You might want to initialise your Random outside the for loop, as random is not actually really random. and it seems to be a duplicate for: https://stackoverflow.com/questions/363681/how-do-i-generate-random-integers-within-a-specific-range-in-java – Ivonet Dec 10 '17 at 23:24

1 Answers1

0

Your attempt at selecting exactly 20 buttons randomly is incorrect.

You have a multidimensional array in Java containing 100 JButtons, in a 10x10 grid like so:

buttons = [
    [JButton0, JButton1, ..., JButton9],
    ...
    [JButton89, JButton90, ..., JButton99]
]

And you want to select 20 buttons randomly. But in the code you provided, you are iterating over all the buttons, and inside the loop you are generating a random number and checking if this iteration matches the random number.

This is wrong, you should randomly select 20 unique indexes, and individually change the buttons at those random indexes.

Here's some code that will will selected 20 buttons by random from a multidimensional array.

JButton[][] buttons = new JButton[10][10]; // Array of 100 JButtons
int totalButtons = 0;                      // Length of total buttons
for (int i = 0; i < buttons.length; ++i) { // Count the length of total buttons
    if (i == 0) {
        totalButtons = buttons[i].length;
    } else {
        totalButtons += buttons[i].length;
    }
}
int[] randomIndex = new int[20];            // 20 random button indexes

// Fill random indexes
Random random = new Random();                         // Generate a random
for (int i = 0; i < randomIndex.length; ++i) {        // Iterate over randomIndex array
    int randomInt = random.nextInt(totalButtons);     // Get a random integer from the random

    for (int j = 0; j < i; ++j) {                     // Iterate over randomIndex array but no further than i
        if (randomInt == randomIndex[j]) {            // Check if random index already exists
            randomInt = random.nextInt(totalButtons); // If random index already exists, select a different index
            --j;                                      // Do not iterate, check same index again
        }
    }

    randomIndex[i] = randomInt; // Set random index
}

// Change button texts
for (int i : randomIndex) {                // Iterate over random indexes
    int row = i / 10;                      // Get row from index
    int col = i % 10;                      // Get column from index

    buttons[row][col].setText("treasure"); // Modify randomly selected button
}
Ari Seyhun
  • 11,506
  • 16
  • 62
  • 109