Execute an action when an item on the combobox is selected

Question

I have a jcombobox containing item1 and item2  also I have a jtextfield   when I select item1 on my jcombobox I want 30 to appear on my jtextfield while 40 if Item2 was selected    How do I do that

User · Accepted Answer

this is how you do it with ActionLIstener   import java awt FlowLayout  import java awt event     import javax swing     public class MyWind extends JFrame       public MyWind             initialize               private void initialize             setSize 300  300           setLayout new FlowLayout FlowLayout LEFT            setDefaultCloseOperation JFrame EXIT ON CLOSE           final JTextField field   new JTextField            field setSize 200  50           field setText                             JComboBox comboBox   new JComboBox            comboBox setEditable true           comboBox addItem  item1            comboBox addItem  item2                           Create an ActionListener for the JComboBox component                     comboBox addActionListener new ActionListener                 public void actionPerformed ActionEvent event                                          Get the source of the component  which is our combo                    box                                     JComboBox comboBox    JComboBox  event getSource                     Object selected   comboBox getSelectedItem                    if selected toString   equals  item1                    field setText  30                    else if selected toString   equals  item2                        field setText  40                                       getContentPane   add comboBox           getContentPane   add field              public static void main String   args            SwingUtilities invokeLater new Runnable                 public void run                     new MyWind   setVisible true

User · Answer

The simple solution would be to use a ItemListener   When the state changes  you would simply check the currently selected item and set the text accordingly  import java awt BorderLayout  import java awt EventQueue  import java awt event ItemEvent  import java awt event ItemListener  import javax swing JComboBox  import javax swing JFrame  import javax swing JPanel  import javax swing JTextField  import javax swing UIManager  import javax swing UnsupportedLookAndFeelException   public class TestComboBox06        public static void main String   args            new TestComboBox06               public TestComboBox06             EventQueue invokeLater new Runnable                  Override             public void run                     try                       UIManager setLookAndFeel UIManager getSystemLookAndFeelClassName                       catch  ClassNotFoundException ex                      catch  InstantiationException ex                      catch  IllegalAccessException ex                      catch  UnsupportedLookAndFeelException ex                                       JFrame frame   new JFrame  Test                    frame setDefaultCloseOperation JFrame EXIT ON CLOSE                   frame setLayout new BorderLayout                     frame add new TestPane                     frame pack                    frame setLocationRelativeTo null                   frame setVisible true                                         public class TestPane extends JPanel            private JComboBox cb          private JTextField field           public TestPane                 cb   new JComboBox new String    Item 1    Item 2                 field   new JTextField 12                add cb               add field                cb setSelectedItem null                cb addItemListener new ItemListener                      Override                 public void itemStateChanged ItemEvent e                        Object item   cb getSelectedItem                        if   Item 1  equals item                             field setText  20                          else if   Item 2  equals item                             field setText  30                                                                                  A better solution would be to create a custom object that represents the value to be displayed and the value associated with it     Updated  Now I no longer have a 10 month chewing on my ankles  I updated the example to use a ListCellRenderer which is a more correct approach then been lazy and overriding toString  import java awt BorderLayout  import java awt Component  import java awt EventQueue  import java awt event ItemEvent  import java awt event ItemListener  import javax swing DefaultListCellRenderer  import javax swing JComboBox  import javax swing JFrame  import javax swing JList  import javax swing JPanel  import javax swing JTextField  import javax swing UIManager  import javax swing UnsupportedLookAndFeelException   public class TestComboBox06        public static void main String   args            new TestComboBox06               public TestComboBox06             EventQueue invokeLater new Runnable                  Override             public void run                     try                       UIManager setLookAndFeel UIManager getSystemLookAndFeelClassName                       catch  ClassNotFoundException ex                      catch  InstantiationException ex                      catch  IllegalAccessException ex                      catch  UnsupportedLookAndFeelException ex                                       JFrame frame   new JFrame  Test                    frame setDefaultCloseOperation JFrame EXIT ON CLOSE                   frame setLayout new BorderLayout                     frame add new TestPane                     frame pack                    frame setLocationRelativeTo null                   frame setVisible true                                         public class TestPane extends JPanel            private JComboBox cb          private JTextField field           public TestPane                 cb   new JComboBox new Item                    new Item  Item 1    20                     new Item  Item 2    30                  cb setRenderer new ItemCelLRenderer                 field   new JTextField 12                add cb               add field                cb setSelectedItem null                cb addItemListener new ItemListener                      Override                 public void itemStateChanged ItemEvent e                        Item item    Item cb getSelectedItem                        field setText item getValue                                                             public class Item           private String value          private String text           public Item String text  String value                this text   text              this value   value                     public String getText                 return text                     public String getValue                 return value                        public class ItemCelLRenderer extends DefaultListCellRenderer             Override         public Component getListCellRendererComponent JList lt   gt  list  Object value  int index  boolean isSelected  boolean cellHasFocus                super getListCellRendererComponent list  value  index  isSelected  cellHasFocus     To change body of generated methods  choose Tools   Templates              if  value instanceof Item                    setText   Item value  getText                               return this

User · Answer

Not an answer to the original question  but an example to the how-to-make-reusable and working custom renderers without breaking MVC  -      WRONG public class DataWrapper      final Data data     final String description     public DataWrapper Object data  String description           this data   data         this description   description                   Override    public String toString            return description             usage myModel add new DataWrapper data1  data1 getName       It is wrong in a MVC environment  because it is mixing data and view  now the model doesn t contain the data but a wrapper which is introduced for view reasons  That s breaking separation of concerns and encapsulation  every class interacting with the model needs to be aware of the wrapped data    The driving forces for breaking of rules were    keep functionality of the default KeySelectionManager  which is broken by a custom renderer  reuse of the wrapper class  can be applied to any data type    As in Swing a custom renderer is the small coin designed to accomodate for custom visual representation  a default manager which can t cope is     broken  Tweaking design just to accommodate for such a crappy default is the wrong way round  kind of upside-down  The correct is  to implement a coping manager   While re-use is fine  doing so at the price of breaking the basic architecture is not a good bargin   We have a problem in the presentation realm  let s solve it in the presentation realm with the elements designed to solve exactly that problem  As you might have guessed  SwingX already has such a solution  -    In SwingX  the provider of a string representation is called StringValue  and all default renderers take such a StringValue to configure themselves   StringValue sv   new StringValue           Override      public String getString Object value            if  value instanceof Data                return   Data  value  getSomeProperty                      return TO STRING getString value             DefaultListRenderer renderer   new DefaultListRenderer sv     As the defaultRenderer is-a StringValue  implemented to delegate to the given   a well-behaved implementation of KeySelectionManager now can delegate to the renderer to find the appropriate item   public BetterKeySelectionManager implements KeySelectionManager          Override      public int selectionForKey char ch  ComboBoxModel model                            if  getCellRenderer   instance of StringValue                  String text     StringValue  getCellRenderer    getString model getElementAt row                                               Outlined the approach because it is easily implementable even without using SwingX  simply define implement something similar and use it    some provider of a string representation a custom renderer which is configurable by that provider and guarantees to use it in configuring itself a well-behaved keySelectionManager with queries the renderer for its string represention    All except the string provider is reusable as-is  that is exactly one implemenation of the custom renderer and the keySelectionManager   There can be general implementations of the string provider  f i  those formatting value or using bean properties via reflection  And all without breaking basic rules  -

[java] Execute an action when an item on the combobox is selected

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