Question

How do I take a random char element from an existing array and assign it to a new array? I have this code with a testing method but my code only returns an empty array instead of the chars expected.

public static char[] generateHiddenCode(Random rand, int numPositions, char[] symbols) {

char[] arrCode = new char[numPositions];

for (int i=0; i<arrCode.length; ++i) {

arrCode[i] = (char) rand.nextInt(symbols.length); }

return arrCode; }

Test:

   private static void testGenerateHiddenCode() {

boolean error = false;

{ //"randomly" chooses 3 symbols from the list

//We know which 3 will be chosen since we set the seed

Random rand = new Random(123);

int numPositions = 3;

char [] symbols = {'A', 'B', 'C', 'D'};

char [] expected = {'C', 'A', 'D'};

char [] result = MasterMind.generateHiddenCode( rand, numPositions, symbols);

if ( !Arrays.equals( expected, result)) {

System.out.println("1) testGenerateHiddenCode expected: " + Arrays.toString(expected) + " result: " + Arrays.toString(result));

error = true;

}

}

if (error) {

System.out.println("testGenerateHiddenCode failed");

} else {

System.out.println("testGenerateHiddenCode passed");

}

}

Answer 1

There is only one change in generateHiddenCode() method everything else is correct, you were generating a number using rand and casting to char but you are supposed to generate a number from rand and get the character in symbol array present at generated index -

public static char[] generateHiddenCode(Random rand, int numPositions, char[] symbols) {

       char[] arrCode = new char[numPositions];

       for (int i = 0; i < arrCode.length; ++i) {
           // get char from symbol array and assign to arrCode array
           arrCode[i] = symbols[ rand.nextInt(symbols.length)];
       }
       return arrCode;
   }