摆脱ArrayList中的空元素

Question

I've been working on this question for a while and I'm still stumped.

I'm supposed to write a method stutter that takes an ArrayList<String> as a parameter and that replaces every string with two of that string. For example, if the list stores the values {"how", "are", "you?"} before the method is called, it should store the values {"how", "how", "are", "are", "you?", "you?"} after the method finishes executing.

But despite my best efforts I still can't seem to get rid of the empty elements that are in my code.

Any help would be greatly appreciated.

public static ArrayList<String> stutter(ArrayList<String> lst) {
    ArrayList<String> list = new ArrayList<String>();
    int size    = lst.size();
    int intSize = lst.size();
    int inSize  = lst.size();
    int size4   = list.size();
    if (lst.size() == 0) {
       lst.clear();
    } else {
        for (int x = 0; x < size; x++) {
            for (int i = 0; i < 2; i++) {
                lst.add(lst.get(x));
            }
        }
        for (int x = 0; x < intSize ; x++) {
            lst.set(x,"");
        }
        for (int x = inSize - 1; x < size; x++) {
            String oldInfo = lst.get(x);
            list.add(oldInfo);
        }
        list.removeAll("",null);
    }
    return list; 
}

Answer 1

Try this approach:

public void duplicate(final List<String> inputList) {

        final List<String> temp = new ArrayList<>();
        inputList.forEach(element -> {
            temp.add(element);
            temp.add(element);
        });

        inputList.clear();
        inputList.addAll(temp);

}

Basically what I am doing here: another list called temp is used to store each element from your initial list 2 times. After that I just clean the initial list and add new stuff.

Instead of clear and addAll you can just return temp - it contains data as you need. But don't forget to change method return type from void to List<String> in that case.

Happy Coding :)

Answer 2

Try this

public static ArrayList<String> stutter(ArrayList<String> lst) {
        ArrayList<String> list = new ArrayList<String>();
        if (!lst.isEmpty()) {
            for (String string : lst) {
                list.add(string);
                list.add(string);
            }
        }
        return list;
    }
}

this could do what you need , its basically checks list if not empty and duplicate the strings in the list

Answer 3

Following up on already good answers, here is my example with keeping the original sample method signature:

import java.util.List;
import java.util.ArrayList;
import java.util.Arrays;

public class Stutter {
    public static List<String> stutter(final List<String> words) {
        // Create the response array.
        List<String> response = new ArrayList<>();
        // Check for valid arguments. If not, return empty array of words.
        if (words == null || words.size() <= 0) {
            return response;
        }   
        // Iterate over the words that were passed in.
        for (final String word : words) {
            // Add the words twice to the response.
            response.add(word);
            response.add(word);
        }
        // The stutter response.
        return response;
    }
    public static void main(final String[] args) {
        final String[] myWords = { "hello", "world" };
        final List<String> myStutterWords = stutter(new ArrayList<>(Arrays.asList(myWords)));
        for (final String s : myStutterWords) {
            System.out.println(s);
        }
    }
}