[JAVA100 example]014, Drop-down list

Import java.awt.*;


import java.awt.event.*;


import javax.swing.*;


import javax.swing.event.*;


/**


* <p>title: list box </p>


* <p>description: Add elements through the input box and click the "Delete" button to delete the list elements </p>


* <p>copyright:copyright (c) 2003</p>


* <p>Filename:ListDemo.java</p>


* @version 1.0


*/


public class Listdemo extends JPanel


implements Listselectionlistener {


private JList list;


private Defaultlistmodel Listmodel;


private static final String hirestring = "Add";


private static final String firestring = "delete";


private JButton Firebutton;


private JTextField EmployeeName;


public Listdemo () {


Super (New BorderLayout ());


Building list elements for lists


Listmodel = new Defaultlistmodel ();


listmodel.addelement ("Alan sommerer");


listmodel.addelement ("Alison huml");


listmodel.addelement ("Kathy walrath");


listmodel.addelement ("Lisa friendly");


listmodel.addelement ("Mary Campione");


listmodel.addelement ("Sharon zakhour");


//Create a list widget and add the element to the list


list = new JList (Listmodel);


//Set selection mode to Radio


List.setselectionmode (listselectionmodel.single_selection);


//Initializes the location of the selected index at 0, that is, the first element


list.setselectedindex (0);


List.addlistselectionlistener (this);


//Set list can look at 5 elements at the same time


List.setvisiblerowcount (5);


//Add a slider to the list


JScrollPane Listscrollpane = new JScrollPane (list);


JButton Hirebutton = new JButton (hirestring);


Hirelistener Hirelistener = new Hirelistener (Hirebutton);


Hirebutton.setactioncommand (hirestring);


Hirebutton.addactionlistener (Hirelistener);


hirebutton.setenabled (FALSE);


Firebutton = new JButton (firestring);


Firebutton.setactioncommand (firestring);


Firebutton.addactionlistener (New Firelistener ());


EmployeeName = new JTextField (10);


Employeename.addactionlistener (Hirelistener);


employeename.getdocument (). Adddocumentlistener (Hirelistener);


String name = Listmodel.getelementat (


List.getselectedindex ()). ToString ();


//Create a panel


JPanel buttonpane = new JPanel ();


buttonpane.setlayout (New BoxLayout (Buttonpane,


Boxlayout.line_axis));


Buttonpane.add (Firebutton);


Buttonpane.add (Box.createhorizontalstrut (5));


Buttonpane.add (New Jseparator (swingconstants.vertical));


Buttonpane.add (Box.createhorizontalstrut (5));


Buttonpane.add (EmployeeName);


Buttonpane.add (Hirebutton);


Buttonpane.setborder (Borderfactory.createemptyborder (5,5,5,5));


Add (Listscrollpane, borderlayout.center);


Add (Buttonpane, borderlayout.page_end);


　　}


/**


*<br> Class Description: "Add" button to monitor


*<br> class Description: When the "Add" button is clicked, the implementation adds the element to the list box


*/


class Firelistener implements ActionListener {


public void actionperformed (ActionEvent e) {


　　　　


int index = List.getselectedindex ();


Listmodel.remove (index);


int size = Listmodel.getsize ();


if (size = = 0) {//If there is no selection, then the delete button results


firebutton.setenabled (FALSE);


} else {//Select a


if (index = = listmodel.getsize ()) {


//Removal options


index--;


　　　　　　　　}


List.setselectedindex (index);


list.ensureindexisvisible (index);


　　　　　　}


　　　　}


　　}


/**


*<br> class Description: "Delete" button listener event


*<br> Class Description: Implementing Delete list elements


*/


class Hirelistener implements ActionListener, Documentlistener {


Private Boolean alreadyenabled = false;


private JButton button;


Public Hirelistener (JButton button) {


This.button = button;


　　　　}


ActionListener must be implemented.


public void actionperformed (ActionEvent e) {


String name = Employeename.gettext ();


//If input is empty or has the same name


if (Name.equals ("") | | Alreadyinlist (name)) {


Toolkit.getdefaulttoolkit (). Beep ();


Employeename.requestfocusinwindow ();


Employeename.selectall ();


return;


　　　　　　}


int index = List.getselectedindex (); Get the selection


if (index = = 1) {//If there is no selection, insert it into the first


index = 0;


} else {//If there is a selection, then insert to the back of the selection


index++;


　　　　　　}


Listmodel.insertelementat (Employeename.gettext (), index);





//Reset Text


Employeename.requestfocusinwindow ();


Employeename.settext ("");


//select new element and show it


List.setselectedindex (index);


list.ensureindexisvisible (index);


　　　　}


/**


*<br> Method Description: Detect whether there are duplicate elements in the list


*<br> input parameter: String name Detection name


*<br> return Type: Boolean Boolean value, if present returns True


*/


protected Boolean alreadyinlist (String name) {


return Listmodel.contains (name);


　　　　}


/**


*<br> Method Description: Implement the Documentlistener interface, the method that must be implemented


*<br> input Parameters:


*<br> return type:


*/


public void Insertupdate (Documentevent e) {


Enablebutton ();


　　　　}


/**


*<br> Method Description: Implement the Documentlistener interface, the method that must be implemented


*<br> input Parameters:


*<br> return type:


*/


public void Removeupdate (Documentevent e) {


Handleemptytextfield (e);


　　　　}


/**


*<br> Method Description: Implement the Documentlistener interface, the method that must be implemented


*<br> input Parameters:


*<br> return type:


*/


public void Changedupdate (Documentevent e) {


if (!handleemptytextfield (e)) {


Enablebutton ();


　　　　　　}


　　　　}


/**


*<br> Method Description: button to enable


*<br> input Parameters:


*<br> return type:


*/


private void Enablebutton () {


if (!alreadyenabled) {


button.setenabled (TRUE);


　　　　　　}


　　　　}


/**


*<br> Method Description: Implement the Documentlistener interface, must implement the method, modify the state of the button


*<br> input Parameters:


*<br> return type:


*/


Private Boolean Handleemptytextfield (Documentevent e) {


if (E.getdocument (). GetLength () <= 0) {


button.setenabled (FALSE);


alreadyenabled = false;


return true;


　　　　　　}


return false;


　　　　}


　　}


/**


*<br> Method Description: Implement the Listselectionlistener interface, the method that must be implemented


*<br> input Parameters:


*<br> return type:


*/


public void valuechanged (Listselectionevent e) {


if (e.getvalueisadjusting () = False) {


if (list.getselectedindex () = = 1) {


firebutton.setenabled (FALSE);


} else {


firebutton.setenabled (TRUE);


　　　　　　}


　　　　}


　　}


/**


*<br> Method Description: Main method


*<br> Input Parameters:


*<br> return type:


*/


public static void Main (string[] args) {


jframe.setdefaultlookandfeeldecorated (TRUE);


//Create a form


JFrame frame = new JFrame ("Listdemo");


frame.setdefaultcloseoperation (jframe.exit_on_close);


//Create a face version


jcomponent Newcontentpane = new Listdemo ();


Newcontentpane.setopaque (TRUE);


Frame.setcontentpane (Newcontentpane);


//Display form


Frame.pack ();


frame.setvisible (TRUE);


　　}


}