How to use KeyListener

Question

I am currently trying to implement a keylistener in my program so that it does an action when I pressed an arrow key  the object in my program either moves left or right   Here is the moving method in my program  public void moveDirection KeyEvent e                int move   0          int r   K getRow            int c   K getCol            if  e getKeyCode      39  move   1    KeyEvent VK RIGHT         if  e getKeyCode      37  move   2    KeyEvent VK LEFT           if  e getKeyCode      KeyEvent VK DOWN  move   3           switch  move                        case 1  if  inBound r  c 1                           K setLocation r  c 1                        if  inBound r  c-1   amp  amp  frame2 r  c-1     K                          frame2 K getRow    K getCol  -1    null                       break    move right 39             case 2  K setLocation K getRow    K getCol  -1   break    move left 37               case 3  b setLocation b getRow   1  b getCol     break    move down             default  return                            processBlockList            I am wondering how the program is supposed to read in  KeyEvent  e  I cannot really type in an arrowkey      Please help    edit  I also need to know what I need to add to my code so that my program waits about 700 milliseconds for a keyinput before moving on to another method

User · Answer

In addition to using KeyListener  as shown by others  answers   sometimes you have to ensure that the JComponent you are using is Focusable  This can be set by adding this to your component if you are subclassing     Override public void setFocusable boolean b        super setFocusable b       And by adding this to your constructor   setFocusable true     Or  if you are calling the function from a parent class container   JComponent childComponent   new JComponent    childComponent setFocusable true     And then doing all the KeyListener stuff mentioned by others

User · Answer

http   docs oracle com javase tutorial uiswing events keylistener html Check this tutorial  If it s a UI based application   then   I also need to know what I need to add to my code so that my program waits about 700 milliseconds for a keyinput before moving on to another method  you can use GlassPane or Timer class to fulfill the requirement   For key Event   public void keyPressed KeyEvent e         int key   e getKeyCode         if  key    KeyEvent VK LEFT            dx   -1             if  key    KeyEvent VK RIGHT            dx   1             if  key    KeyEvent VK UP            dy   -1             if  key    KeyEvent VK DOWN            dy   1            check this game example http   zetcode com tutorials javagamestutorial movingsprites

User · Answer

The class which implements KeyListener interface becomes our custom key event listener  This listener can not directly listen the key events  It can only listen the key events through intermediate objects such as JFrame  So    Make one Key listener class as  class MyListener implements KeyListener         override all the methods of KeyListener interface     Now our class MyKeyListener is ready to listen the key events  But it can not directly do so  Create any object like JFrame object through which MyListener can listen the key events  for that you need to add MyListener object to the JFrame object   JFrame f new JFrame    f addKeyListener new MyKeyListener

User · Answer

Here is an SSCCE    package experiment   import java awt event KeyEvent  import java awt event KeyListener  import javax swing JFrame  import javax swing JLabel  import javax swing JPanel   public class KeyListenerTester extends JFrame implements KeyListener        JLabel label       public KeyListenerTester String s            super s           JPanel p   new JPanel            label   new JLabel  Key Listener             p add label           add p           addKeyListener this           setSize 200  100           setVisible true                Override     public void keyTyped KeyEvent e             if  e getKeyCode      KeyEvent VK RIGHT                System out println  Right key typed                      if  e getKeyCode      KeyEvent VK LEFT                System out println  Left key typed                           Override     public void keyPressed KeyEvent e             if  e getKeyCode      KeyEvent VK RIGHT                System out println  Right key pressed                      if  e getKeyCode      KeyEvent VK LEFT                System out println  Left key pressed                           Override     public void keyReleased KeyEvent e            if  e getKeyCode      KeyEvent VK RIGHT                System out println  Right key Released                      if  e getKeyCode      KeyEvent VK LEFT                System out println  Left key Released                         public static void main String   args            new KeyListenerTester  Key Listener Tester                Additionally read upon these links   How to Write a Key Listener and How to Use Key Bindings

[java] How to use KeyListener

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