Question

Complete code and answer question in comments:
Package hw4;
import java.util.ArrayList;

public class WordGame {
        /*
         * Returns all strings that appear
         * as a consecutive horizontal or vertical sequence of letters
         * (left-right, right-left, up-down, or down-up)
         * in the array board and also appear in dict.
         * Note that the same word may appear multiple times
         * on the board, and will then be multiple times in 
         * the returned array.
         * 
         * dict is assumed to be in alphabetical order
         * board is assumed to be rectangular
         */
        public static String[] search(String[] dict, char[][] board) {
                /*The following line contains <String>, this means
                 * that the ret is an ArrayList that contains String. It is an 
                 * ArrayList of only Strings. 
                 */
                ArrayList<String> ret = new ArrayList<String>();
                int height = board.length;
                
                // Set width to 0 for an empty board,
                // and to the width for first line otherwise,
                // because we assume the board is a rectangle
                int width = board.length==0 ? 0 : board[0].length;
                
                // TODO Generate substrings of the board
                // and check if they are in the dictionary
                // by calling inDictionary (which you implement).
                // If they are, use ret.add to add them
                // to the array that gets returned.
                // Character.toString, String+char, and String+=char
                // can all be useful here.
                // You may want to see https://docs.oracle.com/javase/8/docs/api/java/lang/String.html
        // and https://docs.oracle.com/javase/8/docs/api/java/lang/Character.html
                //
                // TODO (10% of your grade): if your board
                // has height h and width w, how many strings
                // do you need to check using inDictionary
                // (assume that you do nothing to filter out
                // duplicates or, equivalently, that the board
                // is such that there are no duplicates)
                // ANSWER: 
                // EXPLANATION OF THE ANSWER:

                // This line converts ArrayList<String> to String []
                return ret.toArray(new String[0]);
        }
}

Answer 1

import java.util.ArrayList;

public class WordGame {
  
   public static String[] search(String[] dict, char[][] board) {

       ArrayList<String> ret = new ArrayList<String>();
       int height = board.length;

       int width = board.length == 0 ? 0 : board[0].length;

       for (int r = 0; r < height; r++) { // row

           for (int c = 0; c < width; c++) { // column
              
               String s = Character.toString(board[r][c]);
               if (HW4IO.inDictionary(dict, s))   //checks for one-letter words
                   ret.add(s);

               for (int i = c + 1; i < width; i++) { // checking to the right--row doesn't change
                   s += board[r][i];
                   if (HW4IO.inDictionary(dict, s)) // check if s is in the dictionary
                       ret.add(s);

               }
               s = Character.toString(board[r][c]);

               for (int i = c - 1; i >= 0; i--) { // check to the left
                   s += board[r][i];
                   if (HW4IO.inDictionary(dict, s))
                       ret.add(s);

               }
               s = Character.toString(board[r][c]);
               for (int i = r + 1; i < height; i++) { // checking down
                   s += board[i][c];
                   if (HW4IO.inDictionary(dict, s))
                       ret.add(s);

               }

               // r does change when you check up and down
               s = Character.toString(board[r][c]);
               for (int i = r - 1; i >= 0; i--) { // checking up
                   s += board[i][c];
                   if (HW4IO.inDictionary(dict, s))
                       ret.add(s);

               }

           }
       }

       // This line converts ArrayList<String> to String []
       return ret.toArray(new String[0]);
   }
}