Fixed

package stackoverflowtests;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingConstants;
import java.awt.Font;
import javax.swing.JTextField;
import java.awt.Color;
import java.awt.Dimension;

import javax.swing.JButton;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class GuessingGame extends JFrame {
    private static final long serialVersionUID = 1L;
    private JLabel lblOutput;
    private int theNumber;


    private JTextField txtGuess;


    public void checkGuess() {
        String guessText = txtGuess.getText();
        txtGuess.setText("");//Empties the contents of the text field.
        String message = "";
        int guess = Integer.parseInt(guessText);
        if (guess < theNumber)
            message = guess + " is too low. Try again.";
        else if (guess > theNumber)
            message = guess + " is too high. Try again.";
        else {
            message = guess + " is correct. Let's play again!";
            newGame();
        }
        lblOutput.setText(message);
    }

    public void newGame() {
        theNumber = (int) (Math.random() * 100 + 1);
    }

    public GuessingGame() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setTitle("Tim's Hi-Lo Guessing Game");
        getContentPane().setLayout(null);

        JLabel lblNewLabel = new JLabel("Tim's Hi-Lo Guessing Game");
        lblNewLabel.setFont(new Font("Tahoma", Font.BOLD, 15));
        lblNewLabel.setHorizontalAlignment(SwingConstants.CENTER);
        lblNewLabel.setBounds(0, 10, 436, 32);
        getContentPane().add(lblNewLabel);

        JLabel lblNewLabel_1 = new JLabel("Guess a number between 1 and 100:");
        lblNewLabel_1.setBackground(new Color(240, 240, 240));
        lblNewLabel_1.setHorizontalAlignment(SwingConstants.RIGHT);
        lblNewLabel_1.setBounds(147, 54, 215, 13);
        getContentPane().add(lblNewLabel_1);

        txtGuess = new JTextField();
        txtGuess.addActionListener((ActionEvent e) -> {
            checkGuess();
        });
        txtGuess.setHorizontalAlignment(SwingConstants.RIGHT);
        txtGuess.setBounds(260, 122, 27, 19);
        getContentPane().add(txtGuess);
        txtGuess.setColumns(10);

        JButton btnGuess = new JButton("Guess!");
        btnGuess.addActionListener((ActionEvent e) -> {
            checkGuess();
        });
        btnGuess.setBounds(172, 121, 85, 21);
        getContentPane().add(btnGuess);

        lblOutput = new JLabel("Enter a number above and click Guess!");
        lblOutput.setHorizontalAlignment(SwingConstants.CENTER);
        lblOutput.setBounds(58, 196, 350, 13);
        getContentPane().add(lblOutput);
    }

    public static void main(String[] args) {
        GuessingGame theGame = new GuessingGame();
        theGame.newGame();
        theGame.setSize(new Dimension(450, 300));
        theGame.setVisible(true);

    }

}