Java Swing - How to get the value of text in a Tex

问题:

Okay, beginner Java coder here. I'm trying to make a multi-purpose math utility application with Java Swing. One of the things I want it to do is be able to solve basic logarithms. I have the logic all down, but I'm having trouble with the outputting itself. I have a class (named "LogTab") and within it is a nested static class (named "LogPanel") for the actual input area. The button is outside the LogPanel class, and when I press it I want it to be able to take the values of the TextFields inside the LogTab (named "logBase" and "logNum"), calculate them, and send them to an output class. I have everything fine and working except for the part where I take the values from the TextFields.

Here's my code.

public class LogTab extends JPanel {

@SuppressWarnings("serial")
static class LogInput extends JComponent {

    public LogInput() {
        JComponent logInputPanel = new JPanel();
        setLayout(new GridBagLayout());

        JTextField logLbl = new JTextField();
        logLbl.setText("Log");
        logLbl.setEditable(false);
        JTextField logBase = new JTextField(1);
        JTextField logNum = new JTextField(5);

        GridBagConstraints lgc = new GridBagConstraints();

        lgc.weightx = 0.5;
        lgc.weighty = 0.5;

        lgc.gridx = 0;
        lgc.gridy = 0;
        add(logLbl,lgc);

        lgc.gridx = 1;
        lgc.gridy = 1;
        add(logBase,lgc);

        lgc.gridx = 2;
        lgc.gridy = 0;
        add(logNum,lgc);
    }
}

public LogTab() {
    // Set Layout
    setLayout(new GridBagLayout());

    // Create components
    JLabel promptLabel = new JLabel("Enter Logarithm: ");
    JButton solveButton = new JButton("Solve");
    final LogInput logInput = new LogInput();
    solveButton.addActionListener(new ActionListener() {

        @Override
        public void actionPerformed(ActionEvent e) {
            try {
                double base = Double.valueOf(logInput.logBase.getText());
                double num = Double.valueOf(logInput.logNum.getText());
                OutputPanel.outputField.setText(String.valueOf(solve(base,num)));
            } finally {
            }

        }

    });



    // Code that adds the components, bla bla bla




}

public double solve(double base, double num) {
    return (Math.log(base)/Math.log(num));
}
}

When I try to compile this (through Eclipse, by the way), I get an error saying that "logBase/logNum can not be resolved or is not a field". How would I change this so that my ActionListener can get the text from the TextFields?

Thanks

P.S. This is my first question on Stack Overflow, so if I messed something up, tell me :)

回答1:

Make logBase and logNum instance fields...

static class LogInput extends JComponent {

    private JTextField logBase;
    private JTextField logNum;

    public LogInput() {
        JComponent logInputPanel = new JPanel();
        setLayout(new GridBagLayout());

        JLabel logLbl = new JLabel("Log");
        logBase = new JTextField(1);
        logNum = new JTextField(5);

Now add some getters...

public double getBase() {
    String text = logBase.getText();
    if (text.trim().isEmpty()) {
        text = "0";
    }
    return Double.parseDouble(text);
}

public double getNumber() {
    String text = logNum.getText();
    if (text.trim().isEmpty()) {
        text = "0";
    }
    return Double.parseDouble(text);
}

Now you can access the values of logBase and logNum from any instance of LogInput

About this point, I'm thinking that either a JSpinner or JTextField would be a better idea, as they have the ability to validate the input themselves. See How to Use Spinners and How to Use Formatted Text Fields for more details

回答2:

The issue is that the scope of logBase and logNum is limited only to the constructor, and therefore is not accessible by other methods.

Make logBase and logNum fields of LogInput:

static class LogInput extends JComponent {
    JTextField logBase, logNum;

And in the constructor, remove the JTextField identifier:

logBase = new JTextField(1);
logNum = new JTextField(5);