Given a dictionary consisting of many roots and a sentence consisting of words separated by spaces, replace all the derivatives in the sentence with the root forming it. If a derivative can be replaced by more than one root, replace it with the root that has the shortest length.

I want get output [a a b c].

Why is my code exceeding its time limit and showing no output? I think logic is right.

import java.util.*;

public class Main {
    public static void main(String[] args) {
        List<String> dictionary = new ArrayList();
        dictionary.add("a");
        dictionary.add("b");
        dictionary.add("c");

        String sentence = new String("aadsfasf absbs bbab cadsfafs");
        int i = 0;
        int x = 0;
        String t = new String();
        String h = new String();

        while (i < dictionary.size()) {
            t = dictionary.get(i);
            h = sentence.substring(x);

            x = h.indexOf(t);
            int g = x;

            String ij = new String();
            if (x != -1)
                while (g < h.length() && h.charAt(g) != ' ') {
                    ij = ij.concat(Character.toString(h.charAt(g)));
                    g++;
                } else {
                    i++;
                    continue;
                    x = 0;
                }
            x = x + t.length();
            sentence = sentence.replace(ij, t);
        }

        System.out.println(sentence);
    }
}