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I have just started learning basic Java. I would like to know what I can do to improve my coding habits in Java and how to code more efficiently. In this code example, I took code from Very simple Hangman game and made some edits. Most noticeably, I created a GUI to display the game. I do not think I am too good with Java and I would like to get better. Are there any suggestions on how I can improve my coding ability in Java?

import java.util.ArrayList;
import java.util.List;
import javax.swing.*;
import java.awt.event.*;
//This code will use arrays, lists, and some basic GUI with functionality.
public class Hangman{
    /*This list has asterisks for the letters not found and letters for the letters found. This list will be looped through in order to display
      what is known and unknown about the word so far. */
    static List<String> phrases=new ArrayList<String>(); 
    //This JFrame will be used to create a GUI window.
    static JFrame jFrame=new JFrame(); 
    /*This is the primary label which will display the list phrases. After the player guesses the whole word, this variable 
      will also be used to display a text telling what the final word is and also how many mistakes the player made when guessing the word. */ 
    static JLabel label=new JLabel(""); 
    /*This label will only be used to tell the player if the letter the player guessed is not in the word or if the letter the player guessed
    is already in the world */
    static JLabel complementaryLabel=new JLabel(""); 
    /*This will be the text field where the player inputs the player's answer. If the enter key is pressed in the text field, the text in the 
    text field is then processed.*/
    static JTextField textArea=new JTextField("");
    static char userInput;
    //When this button is clicked, the text in the text field is then processed.
    static JButton button=new JButton("Enter");
    static boolean wordIsGuessed = false;
    //This boolean will determine if text in the text field is being processed.
    static boolean buttonPressed=false;
    public static void main(String[] args) {
        //GUI elements are created.
        jFrame.setResizable(false);
        jFrame.setLayout(null);
        jFrame.setSize(600, 900);
        jFrame.setVisible(true);
        jFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        label.setBounds(150, 225, 400, 400);
        complementaryLabel.setBounds(150, 450, 400, 400);
        textArea.setBounds(150, 600, 25, 25);
        textArea.setFocusable(true);
        button.setBounds(200, 600, 100, 25);
        jFrame.add(label);
        jFrame.add(complementaryLabel);
        jFrame.add(textArea);
        jFrame.add(button);


        String[] words = {"writer", "that", "program", "nervous","clarinet"};

        // Pick random index of words array
        int randomWordNumber = (int) (Math.random() * words.length);
        // Create an array to store already entered letters
        char[] enteredLetters=new char[words[randomWordNumber].length()];
        int triesCount = 0;

        //When this button is clicked, the function CheckString is called.
        button.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                CheckString();
            }
        });
        /*The textArea variable can use the button's action listener. When the enter key is pressed inside the text field, 
        the function CheckString is called. */
        textArea.addActionListener(button.getActionListeners()[0]);
        do {
        // infinitely iterate through cycle as long as enterLetter returns true
        // if enterLetter returns false that means user guessed all the letters
        // in the word e. g. no asterisks were displayed by printWord
        switch (enterLetter(words[randomWordNumber], enteredLetters)) {
            case 0:
                triesCount++;
                break;
            case 1:
                triesCount++;
                break;
            case 2:
                break;
            case 3:
                wordIsGuessed = true;
                //The button and the text field are hidden to prevent further input from the player.
                button.setVisible(false);
                textArea.setVisible(false);
                break;
        }
        } while (! wordIsGuessed);

        label.setText("\nThe word is " + words[randomWordNumber] +
            ". You missed " + (triesCount -findEmptyPosition(enteredLetters)) +
            " time(s).");
      //The complementaryLabel is not needed now, so it is set to an empty string to hide this label.
        complementaryLabel.setText("");
    }

    /* Hint user to enter a guess letter,
    returns 0 if letter entered is not in the word (counts as try),
    returns 1 if letter were entered 1st time (counts as try),
    returns 2 if already guessed letter was REentered,
    returns 3 if all letters were guessed */
    public static int enterLetter(String word, char[] enteredLetters)    {
        //The old text in the list is first cleared before new text is added.
        phrases.clear();
        //Strings are added to the phrases list
        phrases.add("Enter a letter in word ");
        // If-clause is true if no asterisks were displayed so
        // word is successfully guessed
        if (! printWord(word, enteredLetters))
            return 3;

        /*Sentence is a string variable that will be equal to the concatenated version of all the strings inside the phrases list.
         This variable will be used to display the whole sentence that was broken down into individual pieces inside the phrases list.
          */
        String sentence="";
        for (int i=0; i<phrases.size(); i++) {
            sentence+=phrases.get(i);
        }
       label.setText(sentence);
        int emptyPosition = findEmptyPosition(enteredLetters);

        //The code inside the if statement will only execute if the text inside the text field is being processed.
       if(buttonPressed) {
        if (inEnteredLetters(userInput, enteredLetters)) {
            //The complementaryLabel displays to the player that the letter the player inputed is already in the word.
            complementaryLabel.setText(userInput+" is already in the word");
            //This variable is set to false, which means that the text inside the text field is not being processed any more.
            buttonPressed=false;

            return 2;
        }
        else if (word.contains(String.valueOf(userInput))) {
            enteredLetters[emptyPosition] = userInput;
            //The complementaryLabel is not needed now, so it is set to an empty string to hide this label.
            complementaryLabel.setText("");
            //This variable is set to false, which means that the text inside the text field is not being processed any more.
            buttonPressed=false;

            return 1;
        }
        else {
            //The complementaryLabel displays to the player that the letter the player inputed is not in the word.
            complementaryLabel.setText(userInput + " is not in the word");
             //Button pressed is set to false, which means that the text inside the text field is not being processed any more.
            buttonPressed=false;

            return 0;
            }

       }
       return 2;

    }

    /* Displays word with asterisks for hidden letters, returns true if
    asterisks were printed, otherwise return false */
    public static boolean printWord(String word, char[] enteredLetters) {
        // Iterate through all letters in word
        boolean asteriskPrinted = false;
        for (int i = 0; i < word.length(); i++) {
            char letter = word.charAt(i);
            // Check if letter already have been entered by the user before
            if (inEnteredLetters(letter, enteredLetters)) {
                phrases.add(String.valueOf(letter));// If yes - add it to the phrases list for displaying
            }
            else {
                phrases.add("*"); //Asterisks are added to the phrases lists for letters that are not found by the player yet.
                asteriskPrinted = true;
            }
        }
        return asteriskPrinted;
    }
    /*This function is called when the player presses the Enter key in the text field or when the player clicks on the enter button.
      The main purpose of this function is to get what is needed from the player's input to use for processing.
     */
    public static void CheckString() {
            /* It is possible for the player to input a value that will cause an error in the code. The value that can cause an error in this
               code would be ''. This is because userInput will not find anything in textArea.getText().charAt(0). Therefore, the try and catch
               method is used to avoid errors.
             */
            try {
             userInput=textArea.getText().charAt(0);
            }
            catch(Exception err) {
                return;
            }
            //If the userInput is not empty, it will be readied for processing.
             if(userInput!=' ') {
                 buttonPressed=true;
                 /*After the player inputs text for processing, the string inside the textArea will be deleted. This is not necessarily 
                  * required, but it is a nice feature.
                  */
                textArea.setText(null);
             }
    }
    /* Check if letter is in enteredLetters array */
    public static boolean inEnteredLetters(char letter, char[] enteredLetters) {
        return new String(enteredLetters).contains(String.valueOf(letter));
    }

    /* Find first empty position in array of entered letters (one with code \u0000) */ 
    public static int findEmptyPosition(char[] enteredLetters) {
        int i = 0;

        //This for loop goes through all the elements inside the function and it is used to find the first empty space in the array. 
        for(int iterator=0; iterator<enteredLetters.length; iterator++) { 
            if(enteredLetters[iterator]=='\u0000') break;
            i++;
        }
        return i;
    }



}
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  • Naming conventions: method names should start with lower case letters, since upper case indicates class names (e.g. checkString() instead of CheckString()). For this reason, the code highlighting here in StackExchange highlights your method name in blue, as if it was a class name. This would probably cause confusion, if another developer wanted to collaborate with you on your code. You can find a list of naming conventions here.
  • Magic numbers: you should avoid using hard-coded numbers. For example, yourenterLetter method returns magic numbers. This makes code less readable, harder to understand and harder to maintain.
  • Method length: it is good practice to keep methods as short and simple as possible. A method should ideally only have one single purpose and a name that indicates this purpose. You already split up your code in different methods, which is a good start. Still, your main and enterLetter methods are quite long and for the enterLetter method, it is hard to get a quick overview of what the method actually does.
  • Access modifiers: Java has different access modifiers for methods and variables. Methods should only be declared as public if they are either the main method, or if you need to call them from another class. Since you have only one single class, you can make all methods and fields private except for the main method.
  • Object orientation: Java is an object-oriented language. The main advantage of this is that code becomes more readable and maintainable if you split your program code into different classes. Just think about which data/functionality belongs together and encapsulate it in a separate class.
  • Separation of concerns: in your code, everything is mixed up in a single class. It is good practice to separate GUI from program logic. A common design pattern used to achieve this is the Model-View-Controller pattern (MVC).
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