Question

java 画一个文本框，为什么没办法显示出来

package aaa;

import java.awt.TextField;

import javax.swing.ButtonGroup;
import javax.swing.JComboBox;
import javax.swing.JDialog;
import javax.swing.JFormattedTextField;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JRadioButton;
import javax.swing.JTextArea;
import javax.swing.JTextField;

public class hh extends JFrame
{

private JTextField userIDField;
private JTextField nameField;
private JTextField phoneField;
private JFormattedTextField birthdayField;
private JTextField emailField;
private JTextField qqField;
private JTextField majorField;
private JTextField positionField;
private JTextField a;
private ButtonGroup group;
private JRadioButton maleButton;
private JRadioButton femaleButton;
private JTextArea summaryArea;
private JComboBox deptField;
private JComboBox placeField;

private JLabel picLabel ;
private JDialog dialog = null ;
private String nations[] = {"hangzhou"};

public static void main(String[] args)

{

hh h=new hh ();
h.setSize(800, 400);
h.show();

TextField a;

a = null;

a.setText("这里是文本框，显示一些东西");
a.setBounds(40, 110, 100, 20);
h.add(a);
}

private hh buildStudentFromField()
{
String userid = userIDField.getText();
return null;

}

}

Answer 1

原因是你的文本框没有创建一个实例，程序都报错了。
TextField a;
a = null;
改成
TextField a = new TextField ();