Java JTextfield 只给我空数据

Question

我制作了一个Mainmenu JFrame，它可以生成4个不同的新框架来代表每个菜单。主菜单框架工作正常。但我发现它无法从新框架文本字段获取文本。这是错误报告和源代码。请让我知道如何修复它。

import java.awt.BorderLayout;
import java.awt.GridLayout;
import java.awt.TextField;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.WindowConstants;
import javax.swing.JTable;


public class PhoneBook extends JFrame implements ActionListener
{

    private String[] colName;


    JPanel panel_main;
    JPanel panel_phbook;
    JPanel panel_numb;
    JPanel panel_grp;

    JButton btn_main_phb;
    JButton btn_main_name;
    JButton btn_main_numb;
    JButton btn_main_grp;


    JTextArea ta_name_serch;
    TextField tf_name_input;

    JButton btn_name_search;
    JButton btn_name_cancel;
    JButton btn_name_modify;
    JButton btn_name_del;
    JButton btn_name_send;

    JTextArea ta_numb_serch;
    TextField tf_numb_input;

    JButton btn_numb_search;
    JButton btn_numb_cancel;
    JButton btn_numb_modify;
    JButton btn_numb_del;
    JButton btn_numb_send;

    JButton btn_grp_search;
    JButton btn_grp_cancel;
    JButton btn_grp_modify;
    JButton btn_grp_del;
    JButton btn_grp_send;
    private JTable table;




    public static void main(String[] args) 
    {
        PhoneBook frame = new PhoneBook();

    }
    public PhoneBook() 
    {

        colName = new String[3];

        panel_main = new JPanel();
        panel_main.setLayout(new GridLayout());

        btn_main_phb = new JButton("phonbook");
        btn_main_name = new JButton("name");
        btn_main_numb = new JButton("number");
        btn_main_grp = new JButton("grp");

        btn_main_phb.addActionListener(this);
        btn_main_name.addActionListener(this);
        btn_main_numb.addActionListener(this);
        btn_main_grp.addActionListener(this);


        panel_main.add(btn_main_phb);
        panel_main.add(btn_main_name);
        panel_main.add(btn_main_numb);
        panel_main.add(btn_main_grp);





//      table = new JTable();
//      table.setColumnSelectionAllowed(true);
//      panel_main.add(table);
//      table.set


        panel_phbook = new JPanel();
        panel_phbook.setLayout(new GridLayout());


        //      panel_phbook.add(btn_main_phb);
//      panel_phbook.add(btn_main_name);
//      panel_phbook.add(btn_main_numb);
//      panel_phbook.add(btn_main_grp);

        btn_name_search = new JButton("Serch");
        btn_name_cancel = new JButton("Serch Cancel");
        btn_name_modify = new JButton("Modi");
        btn_name_del = new JButton("del");
        btn_name_send = new JButton("sms send");

        TextField tf_name_input = new TextField();
        panel_phbook.add(tf_name_input);
        panel_phbook.add(btn_name_search);
        btn_name_search.addActionListener(this);

//      

        panel_numb = new JPanel();
        panel_grp = new JPanel();

        //getContentPane().setLayout(BorderLayout());
        getContentPane().setLayout(new BorderLayout());
        setLocation(500, 400);
        getContentPane().add(panel_main);
        setSize(650,150);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setVisible(true);

    }



    @Override       public void actionPerformed(ActionEvent e) {
        // TODO Auto-generated method stub
        if(e.getSource().equals(btn_main_phb))
        {

            JFrame frame2 = new JFrame();
            frame2.getContentPane().add(panel_phbook);
            frame2.setLocation(400, 300);
            frame2.setSize(500,400);
            setDefaultCloseOperation(EXIT_ON_CLOSE);
            frame2.setVisible(true);

        }
        else if(e.getSource().equals(btn_main_name))
        {

        }
        else if(e.getSource().equals(btn_main_numb))
        {

        }
        else if(e.getSource().equals(btn_main_grp))
        {

        }
        else if(e.getSource().equals(btn_name_search))//this is the problem
        {
            System.out.println(tf_name_input.getText());
        }
    }

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException at PhoneBook.actionPerformed(PhoneBook.java:166) at javax.swing.AbstractButton.fireActionPerformed(Unknown Source) at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source) at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source) at javax.swing.DefaultButtonModel.setPressed(Unknown Source) at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source) at java.awt.Component.processMouseEvent(Unknown Source) at javax.swing.JComponent.processMouseEvent(Unknown Source) at java.awt.Component.processEvent(Unknown Source) at java.awt.Container.processEvent(Unknown Source) at java.awt.Component.dispatchEventImpl(Unknown Source) at java.awt.Container.dispatchEventImpl(Unknown Source) at java.awt.Component.dispatchEvent(Unknown Source) at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source) at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source) at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source) at java.awt.Container.dispatchEventImpl(Unknown Source) at java.awt.Window.dispatchEventImpl(Unknown Source) at java.awt.Component.dispatchEvent(Unknown Source) at java.awt.EventQueue.dispatchEventImpl(Unknown Source) at java.awt.EventQueue.access$200(Unknown Source) at java.awt.EventQueue$3.run(Unknown Source) at java.awt.EventQueue$3.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source) at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source) at java.awt.EventQueue$4.run(Unknown Source) at java.awt.EventQueue$4.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source) at java.awt.EventQueue.dispatchEvent(Unknown Source) at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source) at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source) at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source) at java.awt.EventDispatchThread.pumpEvents(Unknown Source) at java.awt.EventDispatchThread.pumpEvents(Unknown Source)

Answer 1

您遇到此问题的原因是因为您创建了一个与类成员变量之一同名的新局部变量:

TextField tf_name_input = new TextField();

而不是:

tf_name_input = new TextField();