Android随机化字符串而无需重复

Question

I'm doing a simple random quiz app in Android. So basically I have string array of words. I need to display the string without repetition. This is what I've tried so far:

String[] words = { "Welcome", "Different", "Teenager", "Transfer", "Italian", 
                   "Timber", "Toxic", "Illiterate", "Irate", "Moderate", "Transportation", "Attention" };


ArrayList<String> wordlist = new ArrayList<String>();
for (String i : words) 
    wordlist.add(i);
Collections.shuffle(wordlist);

randomStr = words[new Random().nextInt(words.length)];

tvWord.setText("");
tvWord.setText(randomStr);

But I still get the random word repeating. What am I doing wrong in here? Any ideas? I would gladly appreciate your help. Thanks.

Update:

First on a button click the word should then display. And many times I click the button I keep getting the same word again.

 switch(v.getId()){
    case R.id.btPlay:
        randomWordList();
        break;
 }

Where randomWordList(); is the method I posted above.

Answer 1

You don't keep track of what was already used. I also don't understand why you define wordlist and then don't use it. Just a small modification of your code will do the trick.

Edit : You also need to initialize values in different scope than where you use it. For example like this:

public class MyClass{

LinkedList<String> wordlist;

public MyClass(){
    String[] words = { "Welcome", "Different", "Teenager", "Transfer", "Italian", 
               "Timber", "Toxic", "Illiterate", "Irate", "Moderate", "Transportation", "Attention" };
    wordlist = new LinkedList<String>();
    for (String i : words) 
        wordlist.add(i);
    Collections.shuffle(wordlist);
}

public void useNextWord(){
    tvWord.setText("");
    tvWord.setText(wordlist.pollLast());
}

Answer 2

Create a new list of Strings and shuffle it. Then simply iterate over the shuffled list from the beginning.

ArrayList<String> copyOfWords= new ArrayList<String>(words);
Collections.shuffle(copyOfWords);

This is taken from here . Time complexity is O(n).

To iterate over the List you can either get the first element and remove it (with the same method) or keep track which was the last used element.

First solution:

String randomWord = copyOfWords.remove(0);
tvWord.setText(randomWord);

PS do not use this line in your code randomStr = words[new Random().nextInt(words.length)];

Answer 3

You will need to either keep track of the Strings you have already used in another array or list and check the value has not already been used or alternatively remove any used Strings from the pool. You can do that with String next = List.remove(index) .

Answer 4

You first shuffle your list with Collections.shuffle(wordlist); and then access the list with a random index. There's no need to use a random index if the list is already shuffled. Just get one item after another. You could use wordlist.remove(0) until your list is empty.

Display the next string as follows:

if (!wordlist.isEmpty()) {
    randomStr = wordlist.remove(0);
    tvWord.setText(randomStr);
}