在Java中我如何将数组随机化和整型

Question

Hi i am just learning java and want to write a sort of vocabulary trainer. It is working but i want to give the questions in a random order. The trainer pics a list from an external file and splits the file in two parts. It is asking as long the next line isn't null.

for (int i = 0; (zeile = br.readLine()) != null; i++) { 
        splitted = zeile.split(";");                     
        eng[i] = splitted[0];                          
        ger[i] = splitted[1];

then i am asking for the vocabulary. But as you can see its always in the same order. I don't know how i can correctly randomize the list before the asking part.

for (int j = 0; j < eng.length; j++) {

        correct = false;
        while (!correct) {

            System.out.print(eng[j] + " bedeutet: ");

            gerEingabe = vokabel.nextLine(); 

            if (gerEingabe.equals(ger[j])) {
                System.out.println("Das ist Korrekt. Auf zur nächsten Aufgabe.");
                correct = true;
            } else {
                System.out.println("Das war leider Falsch. Bitte versuche es noch ein mal.");

It would be nice if someone can help me with this.

Answer 1

To randomize a List , call Collections.shuffle(List<?> list) .

To get random integers in a defined range, use Random.nextInt(int n) :

Random rnd = new Random();
int val = rnd.nextInt(11) + 5; // Random number 5-15 (inclusive)

Answer 2

Create a small class that holds your translated object. Eg something like below

public class Translation {

     public final String originalWord;
     public final String translatedWord;

     public Translation(String original, String translated) {
         this.originalWord = original;
         this.translatedWord = translated;
     }
}

Then add your translations to an ArrayList<Translation> and leverage Collections.shuffle to randomize the ordering.

List<Translation> list = new ArrayList<>();
while((zeile = br.readLine()) != null) {
    splitted = zeile.split(";");                     
    list.add(new Translation(splitted[0], splitted[1]));
}

Then at the beginning, do the shuffle.

Collections.shuffle(list);

Iteration can be done by index as well via list.get() , you will just need to adapt the rest of the code to work with a Translation object:

   for (int j = 0; j < list.size(); j++) {
     Translation t = list.get(j);
     System.out.print(t.originalWord + " bedeutet: " + t.translatedWord);
   }