Array list in java

Question

I am trying to do this problem but can't get around with it. Please tell me what i did wrong and any tips on how to solving it? Thanks.

here is the problem:

Write a method stutter that takes an ArrayList of Strings and an integer k as parameters and that replaces every string with k copies of that string. For example, if the list stores the values ["how", "are", "you?"] before the method is called and k is 4, it should store the values ["how", "how", "how", "how", "are", "are", "are", "are", "you?", "you?", "you?", "you?"] after the method finishes executing. If k is 0 or negative, the list should be empty after the call.

my code:

 public static void stutter(ArrayList<String> list,int k) {
 String s = "";
 for(int i = 0; i<list.size(); i++) {
 s = list.get(i);
 }
 for(int j = 0; j < k; j++) {
 list.add(j,s);
 }
}

• Paul Lo: Welcome to stackoverflow, you can try to improve the formatting of your code :)

Answer 1

Well...two things are wrong here:

• You're not returning anything, which is a bit of a problem if you want to get back the modified list without changing/destroying your original data.
• Your loops aren't doing anything meaningful. The first loop is only going to give you the last element in your list, and then you only add that k times. Most definitely not what you want.

I won't give the entire thing away, as this is an exercise for you, but here's some suggestions:

• Create your own ArrayList<String> to return instead of that String variable. You'll also be declaring the method to return ArrayList<String>. May as well initialize it, too.

• Read each word in the list passed in. Add that to the local list k times (hint: nested loops). If there's no words to be read, then the loop to add the elements isn't fired.

• user3256022: well as far as i know, i just need to write the method and work it out without return anything. since this is an online assignment so it will tell me if my method is right or wrong when i run it. But thanks, i'll try your tips. Thanks again.
• Makoto: It's pretty bad form to just mutate data passed into a method like that, since something else may be using it. It could be done in-place, but I wouldn't recommend it (or you will get very accustomed to the phrase ConcurrentModificationException if you're not careful).

Answer 2

Here is the code

public static List<String> stutter(ArrayList<String> list,int k) {
 List<String> resultList=new ArrayList<String>(); // creating new list
 if(k<=0) {
 return resultList; //return empty list. Return null if necessary
 } else {
 for(String s : list) { //looping the list input
 for(int i=0;i<k;i++) { 
 resultList.add(s); // adding the same string k times 
 }
 }
 return resultList;
 }
 }

Answer 3

1. Second for loop should be nested in first for loop
2. And strings should be added to a newlist instead of adding them to the samelist

Done modifications to your code.

 public static void stutter(List<String> list,int k) {
 String s = "";
 List<String> newList=new ArrayList<String>();
 if(k>0) {
 for(int i = 0; i<list.size(); i++) {
 s = list.get(i);
 for(int j = 0; j < k; j++) {
 newList.add(s);
 }
 }
 }
 list=newList; // Assigning it your input list since you want to change the actual list
 System.out.println(list.toString()); //Since not returning anything, printing the data
 }