[RESOLVIDO]Problema com this keyword e static

Programação Java
#1

Ola!

Nesta parte de um programa em que estou a resolver, que consiste numa pequena janela de Log-in com nome e password, estou com um problema com a this keyword e com o static e non static. Eu nunca percebi muito bem para que nem como e que a this keyword funciona e o que se passa e que onde diz “textField.addActionListener(this);” , aparece-me um erro:

“non-static variable this cannot be referenced from a static context”. Como eu resolvo isto?

Obrigado

[code]import javax.swing.;
import javax.swing.;
import javax.swing.text.;
import java.awt.;
import java.awt.event.*;
import java.net.URL;
import java.io.IOException;

public class Livraria implements ActionListener
{
private static void addLabelTextRows(JLabel[] labels,JTextField[] textFields, GridBagLayout gridbag,Container container)
{
GridBagConstraints c = new GridBagConstraints();
c.anchor = GridBagConstraints.EAST;
int numLabels = labels.length;

    for (int i = 0; i < numLabels; i++) 
    {
        c.gridwidth = GridBagConstraints.RELATIVE; //next-to-last
        c.fill = GridBagConstraints.NONE;      //reset to default
        c.weightx = 0.0;                       //reset to default
        container.add(labels[i], c);

        c.gridwidth = GridBagConstraints.REMAINDER;     //end row
        c.fill = GridBagConstraints.HORIZONTAL;
        c.weightx = 1.0;
        container.add(textFields[i], c);
    }
}
	

protected static final String name = "Nombre";
protected static final String password = "Clave";
protected JLabel actionLabel;

public static void main (String[] args)
{	

// Create frame
	JFrame frame = new JFrame("Login");
	frame.setSize(400, 200);
    frame.setLocationRelativeTo(null);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  // What to do when the X button is pressed ( Leave ) .

//Textfields  
    JTextField textField = new JTextField(10); // The ten is the size of the box.
    textField.setActionCommand(name);
    textField.addActionListener(this); // <-----AQUI
    
    JPasswordField passwordField = new JPasswordField(10); // The size of the box will be the same as in TextField.
    passwordField.setActionCommand(password);
    
//Create some labels for the fields.
    
    JLabel textFieldLabel = new JLabel(name + ": ");
    textFieldLabel.setLabelFor(textField);
    JLabel passwordFieldLabel = new JLabel(password + ": ");
    passwordFieldLabel.setLabelFor(passwordField);
    
//Lay out the text controls and the labels.
    
    JPanel textControlsPane = new JPanel();
    GridBagLayout gridbag = new GridBagLayout();
    GridBagConstraints c = new GridBagConstraints();

    textControlsPane.setLayout(gridbag); // Layout of the components of the frame.
    
    JLabel[] labels = {textFieldLabel, passwordFieldLabel};
    JTextField[] textFields = {textField, passwordField};
    addLabelTextRows(labels, textFields, gridbag, textControlsPane);
    
    //c.gridwidth = GridBagConstraints.REMAINDER; //last
    //c.anchor = GridBagConstraints.WEST;
    //c.weightx = 1.0;
    
    textControlsPane.setBorder(BorderFactory.createCompoundBorder( // Create the Lines around the Name and Password.
                            BorderFactory.createTitledBorder("Livraria Ideal Login"), // What it says on the lines
                            BorderFactory.createEmptyBorder(15,15,15,15))); // Size of the lines 

    
    
    JPanel leftPane = new JPanel(new BorderLayout());
    leftPane.add(textControlsPane, BorderLayout.PAGE_START);
    frame.add(leftPane, BorderLayout.LINE_START);
      
      
    // Create and show GUI             
    frame.pack();             
    frame.setVisible(true);
       
}

public void actionPerformed(ActionEvent e) 
{
    String prefix = "You typed \"";
    if (name.equals(e.getActionCommand())) 
    {
        JTextField source = (JTextField)e.getSource();
        //actionLabel.setText(prefix + source.getText() + "\"");
        System.out.println(source.getText());
    } 
    else 
    	if (password.equals(e.getActionCommand())) 
    {
        JPasswordField source = (JPasswordField)e.getSource();
        actionLabel.setText(prefix + new String(source.getPassword())+ "\"");
    } 
    
    /*String username = actionLabel.getText();
    System.out.println(username);*/
}

}
[/code]

#2

this se refere à instância, mas o modificador static faz com que o objeto referenciado não dependa de instância. Você não pode usar ambos no mesmo contexto.

http://guj.com.br/java/249865-metodos-estaticos-e-variaveis-de-instancia

#3

O método main é um método estático. Você não pode chamar “this”, que se refere à uma instância, dentro de um método estático. Para contornar esse problema, você pode inicializar seu JTextField dentro de um construtor:

[code]import javax.swing.;
import javax.swing.;
import javax.swing.text.;
import java.awt.;
import java.awt.event.*;
import java.net.URL;
import java.io.IOException;

public class Livraria implements ActionListener
{
private JTextField textField;

    public Livraria()
    {
          textField = new JTextField(10); // The ten is the size of the box.
          textField.setActionCommand(name);
          textField.addActionListener(this); // <-----AQUI
     }

private static void addLabelTextRows(JLabel[] labels,JTextField[] textFields, GridBagLayout gridbag,Container container) 
{
    GridBagConstraints c = new GridBagConstraints();
    c.anchor = GridBagConstraints.EAST;
    int numLabels = labels.length;

    for (int i = 0; i < numLabels; i++) 
    {
        c.gridwidth = GridBagConstraints.RELATIVE; //next-to-last
        c.fill = GridBagConstraints.NONE;      //reset to default
        c.weightx = 0.0;                       //reset to default
        container.add(labels[i], c);

        c.gridwidth = GridBagConstraints.REMAINDER;     //end row
        c.fill = GridBagConstraints.HORIZONTAL;
        c.weightx = 1.0;
        container.add(textFields[i], c);
    }
}
	

protected static final String name = "Nombre";
protected static final String password = "Clave";
protected JLabel actionLabel;

public static void main (String[] args)
{	

// Create frame
JFrame frame = new JFrame("Login");
frame.setSize(400, 200);
    frame.setLocationRelativeTo(null);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  // What to do when the X button is pressed ( Leave ) .

    
    JPasswordField passwordField = new JPasswordField(10); // The size of the box will be the same as in TextField.
    passwordField.setActionCommand(password);
    
//Create some labels for the fields.
    
    JLabel textFieldLabel = new JLabel(name + ": ");
    textFieldLabel.setLabelFor(textField);
    JLabel passwordFieldLabel = new JLabel(password + ": ");
    passwordFieldLabel.setLabelFor(passwordField);
    
//Lay out the text controls and the labels.
    
    JPanel textControlsPane = new JPanel();
    GridBagLayout gridbag = new GridBagLayout();
    GridBagConstraints c = new GridBagConstraints();

    textControlsPane.setLayout(gridbag); // Layout of the components of the frame.
    
    JLabel[] labels = {textFieldLabel, passwordFieldLabel};
    JTextField[] textFields = {textField, passwordField};
    addLabelTextRows(labels, textFields, gridbag, textControlsPane);
    
    //c.gridwidth = GridBagConstraints.REMAINDER; //last
    //c.anchor = GridBagConstraints.WEST;
    //c.weightx = 1.0;
    
    textControlsPane.setBorder(BorderFactory.createCompoundBorder( // Create the Lines around the Name and Password.
                            BorderFactory.createTitledBorder("Livraria Ideal Login"), // What it says on the lines
                            BorderFactory.createEmptyBorder(15,15,15,15))); // Size of the lines 

    
    
    JPanel leftPane = new JPanel(new BorderLayout());
    leftPane.add(textControlsPane, BorderLayout.PAGE_START);
    frame.add(leftPane, BorderLayout.LINE_START);
      
      
    // Create and show GUI             
    frame.pack();             
    frame.setVisible(true);
       
}

public void actionPerformed(ActionEvent e) 
{
    String prefix = "You typed \"";
    if (name.equals(e.getActionCommand())) 
    {
        JTextField source = (JTextField)e.getSource();
        //actionLabel.setText(prefix + source.getText() + "\"");
        System.out.println(source.getText());
    } 
    else 
    	if (password.equals(e.getActionCommand())) 
    {
        JPasswordField source = (JPasswordField)e.getSource();
        actionLabel.setText(prefix + new String(source.getPassword())+ "\"");
    } 
    
    /*String username = actionLabel.getText();
    System.out.println(username);*/
}

}
[/code]

#4

já resolvi! obrigado!

#5