Cannot make this code work properly

Question

How do I make it show answers randomly on one of 4 lines, without having any duplicates?

My current code:

TextView question;
private int qType = -1;
private int asked = 0;
private void QBegin() {
 /*
 * Gets a random question
 */
 question = (TextView) findViewById(R.id.question);
 String[] types = { "Q1", "Q2", "Q3", "Q4", "Q5"};
 Random random = new Random();
 int qType = random.nextInt(types.length);
 question.setText(types[qType]);
 asked++;
 // StringList.add(types[qType]);
 getAnswers(qType);
 /* if(StringList.contains(types[qType]) && asked >= types.length+1){
 asked = 0;
 answerCounter.setText("THE END");
 } else if (StringList.contains(types[qType]) && asked < types.length+1){
 QBegin();
 } */
}
 public static int random(int range) {
 return (int)(java.lang.Math.random() * (range+1));
}
public void shuffle(String input){
 /*
 * Unused shuffle method
 */
 List<Character> characters = new ArrayList<Character>();
 for(char c:input.toCharArray()){
 characters.add(c);
 }
 StringBuilder output = new StringBuilder(input.length());
 while(characters.size()!=0){
 int randPicker = (int)(Math.random()*characters.size());
 output.append(characters.remove(randPicker));
 }
 System.out.println(output.toString());
}
private void getAnswers(int Type) {
 /* 
 * Getting answers here
 */
 int randomValue = random(4);
 try { 
 String answers_list[][] = {
 {"Answer 1-1", "Answer 2-1", "Answer 3-1", "Answer 4-1"}, 
 {"Answer 1-2", "Answer 2-2", "Answer 3-2", "Answer 4-2"},
 {"Answer 1-3", "Answer 2-3", "Answer 3-3", "Answer 4-3"},
 {"Answer 1-4", "Answer 2-4", "Answer 3-4", "Answer 4-4"},
 {"Answer 1-5", "Answer 2-5", "Answer 3-5", "Answer 4-5"}} ;
 answer1.setText(answers_list[Type][randomValue+1 > 3 ? (randomValue+0)-4 : randomValue+0]); 
 answer2.setText(answers_list[Type][randomValue+2 > 3 ? (randomValue+1)-3 : randomValue+1]); 
 answer3.setText(answers_list[Type][randomValue+3 > 3 ? (randomValue+2)-2 : randomValue+2]); 
 answer4.setText(answers_list[Type][randomValue+0 > 3 ? (randomValue+3)-4 : randomValue+3]);
 /*for (int rows = 0; rows < answer&*list.length; rows++){
 for (int cols = 0; cols < answers_list[rows].length; cols++){ 
 }
 }*/
 } catch(Exception ex){
 answer1.setText("Error "+ex);
 }
}

Code that's responsible for picking & adding questions on one of 4 lines (randomly)

 answer1.setText(answers_list[Type][randomValue+1 > 3 ? (randomValue+0)-4 : randomValue+0]); 
 answer2.setText(answers_list[Type][randomValue+2 > 3 ? (randomValue+1)-3 : randomValue+1]); 
 answer3.setText(answers_list[Type][randomValue+3 > 3 ? (randomValue+2)-2 : randomValue+2]); 
 answer4.setText(answers_list[Type][randomValue+0 > 3 ? (randomValue+3)-4 : randomValue+3]);

At the moment, I'm having duplicates with answer1 and answer4. Please Help.

• Dave Newton: It's... unclear what's happening here, or how you're implementing this. Basically you're trying to get a list of four random numbers with no duplicates?
• Alex: Yes, that's what I'm trying to do.

Answer 1

If I understand your goal correctly, you're trying to randomly shuffle a list of questions. Rossum gave you one way to do this and this is a good introduction to the best known options.

In my opinion, this is the simplest approach:

1. Create a map that sorts by key (e.g. TreeMap <Double,String> or <Double,Question>)
2. Add a random key and the question as the value
3. Loop through and print the results. A foreach loop will use the sort order

Don't worry about duplicate random numbers or normalizing it. Dups are unlikely and if you need a question #, add a counter in the loop.

Answer 2

There is a known standard shuffling method.

1. Pick one of the four at random. If necessary, swap the one you picked with the answer at position four.
2. Pick one of the remaining answers 1 to 3 at random. If necessary, swap the one you picked with the answer at position three.
3. Pick one of the remaining answers 1 to 2 at random. If necessary, swap the one you picked with the answer at position two.

You now have a shuffled list containing the original four answers in random order. This algorithm is called the Fisher-Yates shuffle.

ETA simple sample code:

Random rand = new Random();
String[] answers = { "42",
 "Only on a Tuesday.",
 "4ドル.36",
 "Hieronymous K. Sluggenheimer III" };
// Shuffle answers[]
for (int i = 3; i > 0; --i) {
 // Pick an answer that hasn't yet been chosen.
 int pick = rand.nextInt(i + 1);
 if (pick != i) {
 // Exchange answers[i] and answers[pick].
 String temp = answers[i];
 answers[i] = answers[pick];
 answers[pick] = temp;
 }
}

• Alex: Mhmm, can you modify my code for me, cause your statements are a bit confusing for me.
• Alex: This didn't help me as much, to be honest :/