随机生成char数组，没有重复的索引

Question

想要在char数组中生成没有重复索引的随机字符，并将它们存储在新的ArrayList中。ArrayList<Character> al = new ArrayList<>();char letters[ ] = {'a', 'b', 'c', 'd', 'e'};for(int i =0; i<letters.length; i++){    al.add(letters[ i ]);}ArrayList<Character> al2 = new ArrayList<>();Random random = new Random ();while (al.size() > 0) {    int randomizedNumber = random.nextInt(al.size());    al2.add(letters[ randomizedNumber ]; //adding randomized charterer in the new ArrayList.    al.remove(letters[ randomizedNumber ];}