選取隨機數

private List pickItemRandomly(List subjectAll,int number){
List<WncSubject> fiveList = new ArrayList<WncSubject>();
int listSize = subjectAll.size();
if(listSize <= number){
fiveList = subjectAll;
}else{
//取隨機number條數據
HashSet<Integer> set = new HashSet<Integer>();
while(set.size() < number){
int num = (int)(Math.random() * listSize);
Boolean isInsert = set.add(num);
if(isInsert){
fiveList.add(subjectAll.get(num));
}
}
}
return fiveList;
}