构建单词列表处理应用程序的初始版本

Question

I have a question in regards to the following questions.
Now in question 1 down below it wants to create a java class.

1. Create a Java class called Words with the following contents:

import javax.swing.JOptionPane;

public class Words {

public static void main(String[] args) {

WordList ws = new WordList();

 String in = JOptionPane.showInputDialog(

 "Click cancel to end or enter a word and click OK");

 while (in != null) {

ws.addWord(in);

in = JOptionPane.showInputDialog(
 "Click cancel to end or enter a word and click OK");
 }

JOptionPane.showMessageDialog(null, "Word list = " + 

ws.toString());

 JOptionPane.showMessageDialog(null, "First word = " + 

ws.getFirst());

JOptionPane.showMessageDialog(null, "Last word = " + 

ws.getLast());

 }

}

In question 2 it asks the following:

2. Create a Java class called WordList in your existing Practical1 project with the following contents:

3. Right-click in the source code window of the class Words and select "Run File". Enter several words, clicking OK after each one and observe how the program behaves.
   Make sure you understand how the application works.

4. In the class WordList, modify the methods getFirs and getLast as described by the associated comments. The associated comments are down below here from the WordList.java class:

import java.util.ArrayList;

public class WordList {

 private ArrayList<String> theWordList = new ArrayList<String>();

public void addWord(String s) {

theWordList.add(s);

    }

 public String getFirst() {

// Replace the return statement below with a statement

 // that returns

 // the first word of theWordList (the word at index 0).

  // Hint: use the ArrayList method "get".

  // If there is no first word (theWordList has no words in it),
         * "-" should be returned.

//

return "junk";

}


public String getLast() {

 // Replace the string "junk" with the

 // last word of theWordList (the word

 // at index size()-1). Hint: use the ArrayList method "get".

 // If there is no last word (theWordList has no words in it),

  // "-" should be returned.

  //

 return "junk";
}

public String toString() {

 return theWordList.toString();
    }
}

The main questions I am more stuck in is with the comments they have left me in steps to completing question 4. How can I do these questions here??

In case you need the other class which is the main class, here it is and its labeled Words.java:

import javax.swing.JOptionPane;

public class Words {

 public static void main(String[] args) {

  WordList ws = new WordList();

 String in = JOptionPane.showInputDialog(

 "Click cancel to end or enter a word and click OK");

while (in != null) {

  ws.addWord(in);

  in = JOptionPane.showInputDialog(

  "Click cancel to end or enter a word and click OK");
        }

JOptionPane.showMessageDialog(null, "Word list = " + 

ws.toString());

 JOptionPane.showMessageDialog(null, "First word = " + 

ws.getFirst());

JOptionPane.showMessageDialog(null, "Last word = " + 

ws.getLast());


}
}

Answer 1

How to get the contents from an ArrayList

For the first element in public String getFirst() {

if (theWordList.isEmpty ()) {
    return "-";
return theWordList.get (0);  // first element of List

For the last element in public String getLast() {

do the same empty check as above and then return

using theWordList.size () -1