HashMap if containsValue infinite loop issue

Question

I am trying to create a fixture list for a group of 6 teams using hashmaps and arrays. I have an array of 6 teams. Each team must play each other twice. I am removing each team at random from the original list of teams and adding them to a new list. This new list is added to a hashmap. In order to avoid the same list of fixtures occuring more than once i am trying to check this new list before adding it to the hashmap, if it already exists then i dont add it. here is my code so far:

List<String> testList = new ArrayList<String>();
List<String> tempList = new ArrayList<String>();
Random myRandomizer = new Random();
String random1,random2;
tempOrder = new ArrayList<ArrayList<String>>();
HashMap<Integer, ArrayList<String>> map = new HashMap<Integer, ArrayList<String>>();

testList.add("team1");
testList.add("team2");
testList.add("team3");
testList.add("team4");
testList.add("team5");
testList.add("team6");


int x = (testList.size()-1) * 2;
int y = 0;

while(map.size() < 10){
    System.out.println("Match Day " + (y+1));
    //while(tempOrder.size()<10){
    //  System.out.println("Match Day " + (tempOrder.size()+1));
    while(testList.size()>0){
        random1 = testList.get(myRandomizer.nextInt(testList.size()));
        testList.remove(random1);
        tempList.add(random1);
        random2 = testList.get(myRandomizer.nextInt(testList.size()));
        testList.remove(random2);
        tempList.add(random2);

        System.out.println( random1 + " V " + random2 + "\n");
    }

    //tempOrder.add((ArrayList<String>) tempList);

    // add to hashmap
    // check value exists
    // if true add
    // if not dont
    if(!(map.containsValue(tempList))){

        y++;
        map.put(y, (ArrayList<String>) tempList);
        for(String s: tempList){
            testList.add(s);
        }
        tempList.clear();
    //tempOrder.clear();

    }

    else if((map.containsValue(tempList))){
        //System.out.println("issue");
        //tempOrder.clear();
        for(String s: tempList){
            testList.add(s);
        }
        tempList.clear();


    }

I am getting an infinite loop at the moment when i run this code, can someone please help? i think its the right idea but maybe the wrong execution, Is this the correct way to do this?

Thanks in advance

Please format your code - it's much harder to read without indentation. Ideally, you should then convert it to a short but complete program demonstrating the problem. I suspect you can shorten what you've already got, and you can definitely remove the randomness and wrap it up in a complete program — Jon Skeet
– Jon Skeet, Commented Dec 12, 2014 at 14:51

Florent Bayle · Accepted Answer · 2014-12-12 15:12:10Z

2

The problem is that you are creating tempList at the beginning, so tempList will always be the same, and map.containsValue(tempList) will always return true.

Move tempList creation/declaration at the beginning of your while loop:

while (map.size() < 10) {
    List<String> tempList = new ArrayList<String>();
    //...
}

answered Dec 12, 2014 at 15:12

Florent Bayle

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Comments

mpage · Accepted Answer · 2014-12-12 15:37:56Z

You add tempList to your map each time it's unique, but then you call tempList.clear() and wipe it out.

Try this:

    String random1,random2;
    HashMap<Integer, ArrayList<String>> map = new HashMap<Integer, ArrayList<String>>();
    Random myRandomizer = new Random();

    List<String> testList = new ArrayList<String>();
    testList.add("team1");
    testList.add("team2");
    testList.add("team3");
    testList.add("team4");
    testList.add("team5");
    testList.add("team6");

    int y = 0;

    while(map.size() < 10) {
        System.out.println("Match Day " + (y + 1));

        List<String> tempList = new ArrayList<String>();

        while (testList.size() > 0) {
            random1 = testList.get(myRandomizer.nextInt(testList.size()));
            testList.remove(random1);
            tempList.add(random1);
            random2 = testList.get(myRandomizer.nextInt(testList.size()));
            testList.remove(random2);
            tempList.add(random2);

            System.out.println(random1 + " V " + random2 + "\n");
        }

        if (!(map.containsValue(tempList))) {

            y++;
            map.put(y, (ArrayList<String>) tempList);
            for (String s : tempList) {
                testList.add(s);
            }

        } else if ((map.containsValue(tempList))) {
            for (String s : tempList) {
                testList.add(s);
            }
        }
    }

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