I am trying out to code a simple arithmetic game in Java but I faced an error like: Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: For input string. This happens when I clicked on number buttons and cleared them to enter a new number but it seems that the string still contains the previous number I clicked. (For example, I clicked 5 and deleted it so I could enter 9 instead and now the string seems to register it as 59 instead of just 9.) I used .setText('') to clear the text area.

This is my code for when the buttons are pressed:

  public void actionPerformed(ActionEvent e)
    {
        if(e.getActionCommand().equals("one"))
        {
            answerText.append("1");
            userAnswer = userAnswer   "1";  
        }
        // same code for two, three, four... to nine.
        if(e.getActionCommand().equals("enter"))
        {
            int userValue = new Integer(userAnswer);
            if (userValue == rightAnswer)
            {
                score  ;
                userAnswer = "";
                generateRandomProblem();      
            }
            else
            {
                JOptionPane.showMessageDialog(this,"Wrong answer! Please try again.");
            }
        }
    }

The answer variable and delete button is :

        answerText = new JTextArea();
        answerText.setEditable(false);

        clearbtn = new JButton("Clear");
        clearbtn.setActionCommand("clear");
        clearAnswer.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                answerText.setText("");
            }
        }); 

How do I make sure that my answerText is completely clear?

CodePudding user response：

Your error message:

java.lang.NumberFormatException: For input string

This means that you are trying to parse a string into a number, but the string contains something that cannot be parsed into a number. Java prints the content of the string after the text For input string. In this case there's nothing after that text, because the string that you are trying to parse is the empty string - that you set in the text box by calling answerText.setText("");

Solution: Check if the string you are trying to parse is empty before you try to parse it into a number. For example:

if (e.getActionCommand().equals("enter"))
{
    if (!"".equals(userAnswer)) // Check if userAnswer is not empty
    {
        int userValue = new Integer(userAnswer);
        if (userValue == rightAnswer)
        {
            score  ;
            userAnswer = "";
            generateRandomProblem();      
        }
        else
        {
            JOptionPane.showMessageDialog(this,"Wrong answer! Please try again.");
        }
    }
    else
    {
        JOptionPane.showMessageDialog(this, "Please enter a number before pressing Enter.");
    }
}

CodePudding user response：

The variable userAnswer doesn't get cleared when answerText is cleared. This might cause issues.

The exception you are having is probably being cause because int userValue = new Integer(userAnswer); is called at a point where userAnswer is empty (because it can't make a number out of nothing).