Olá a todos!
Veja o código:
//TextFieldFrame.java
//Demonstrating the class JTextField
import java.awt.FlowLayout;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.JPasswordField;
import javax.swing.JOptionPane;
public class TextFieldFrame extends JFrame {
private JTextField textField1; //field of text with size set
private JTextField textField2; //field of text built with text
private JTextField textField3; //field of text with text and size
private JPasswordField passwordField; //field of password with text
//builder TextFieldFrame add JTextFields the JFrame
public TextFieldFrame()
{
super("Testing JTextField and JPasswordField");
setLayout(new FlowLayout()); //sets the layout of frame
//builds textField with 10 columns
textField1 = new JTextField(10);
add(textField2); //add tectField1 to JFrame
//builds field with the text default and 21 columns
textField3 = new JTextField("Uneditable text field",21);
textField3.setEditable(false); //off the edition
add(textField3); //add textField3 to JFrame
//builds passwordField with the text default
passwordField = new JPasswordField("Hidden text");
add(passwordField); //add passwordField to JFrame
//handles of event registers
TextFieldHandler handler = new TextFieldHandler();
textField1.addActionListener(handler);
textField2.addActionListener(handler);
textField3.addActionListener(handler);
passwordField.addActionListener(handler);
}//end construction
//class internal private for treatment of event
private class TextFieldHandler implements ActionListener
{
//process events of field of text
public void actionPerformed(ActionEvent event)
{
String string = ""; //states string the be displayed
//user pressed Enter on JTextField textField1
if(event.getSource() == textField1)
string = String.format("textField1: %s",event.getActionCommand());
//user pressed Enter on JTextField textField2
else if (event.getSource() == textField2)
string = String.format("textField2: %s",event.getActionCommand());
//user pressed Enter on JTextField textField3
else if (event.getSource() == textField3)
string = String.format("textField3: %s",event.getActionCommand());
//user pressed Enter on JTextField passwordField
else if (event.getSource() == passwordField)
string = String.format("passwordField: %s",new String (passwordField.getPassword()));
//display the content of JTextField
JOptionPane.showMessageDialog(null, string);
}
}
}
//TextFieldTest.java
//Testing TextFieldFrame.
import javax.swing.JFrame;
public class TextFieldTest {
public static void main(String args[])
{
TextFieldFrame textFieldFrame = new TextFieldFrame();
textFieldFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
textFieldFrame.setSize(325,100); //sets the size of frame
textFieldFrame.setVisible(true); //display the frame
}
}
Veja o error ao executar:
Exception in thread "main" java.lang.NullPointerException
at java.awt.Container.addImpl(Container.java:1066)
at java.awt.Container.add(Container.java:974)
at javax.swing.JFrame.addImpl(JFrame.java:556)
at java.awt.Container.add(Container.java:377)
at TextFieldFrame.<init>(TextFieldFrame.java:26)
at TextFieldTest.main(TextFieldTest.java:10)
O que está acontecendo ? Não há nenhum error aparente no código. Mas ao executar dá erro.
