Java while loop to draw lines
<p>Hello everyone i am trying to do a exercise from a Java book and what i need to do is draw lines and within a textfield i have to say how far the distance between the lines have to be. All of this has to be in a loop so no hardcoded lines. </p>

<p>i have made everything like i thought it should be done but i get some weird error in my console that is keep coming. the error code is as followed:</p>

<blockquote>
  <p>Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: For input string: ""
      at java.lang.NumberFormatException.forInputString(NumberFormatException.java:48)
      at java.lang.Integer.parseInt(Integer.java:470)
      at java.lang.Integer.parseInt(Integer.java:499)
      at h03.LinePanel.paintComponent(LinePanel.java:30)
      at javax.swing.JComponent.paint(JComponent.java:1037)
      at javax.swing.JComponent._paintImmediately(JComponent.java:5106)
      at javax.swing.JComponent.paintImmediately(JComponent.java:4890)
      at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:812)
      at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:714)
      at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:694)
      at javax.swing.RepaintManager.access$700(RepaintManager.java:41)
      at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1672)
      at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
      at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:702)
      at java.awt.EventQueue.access$400(EventQueue.java:82)
      at java.awt.EventQueue$2.run(EventQueue.java:663)
      at java.awt.EventQueue$2.run(EventQueue.java:661)
      at java.security.AccessController.doPrivileged(Native Method)
      at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
      at java.awt.EventQueue.dispatchEvent(EventQueue.java:672)
      at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:296)
      at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:211)
      at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:201)
      at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:196)
      at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:188)
      at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)</p>
</blockquote>

<p>since i am new to Java i don't know what i did wrong and how to troubleshoot this error so i would appreciate any help! the code in my panel that i use for this is</p>

<pre><code>DrawLines lines = new DrawLines();

public void paintComponent(Graphics g) {

    super.paintComponent(g);
    int positionY = getHeight() - Integer.parseInt(afstand.getText()); // absolut positioning

    int yPos = 0;

    while(yPos &lt;= positionY) {

        lines.drawLines(g, 0, yPos, getWidth(), yPos);
        yPos = yPos + Integer.parseInt(afstand.getText());
    }

}

public void actionPerformed(ActionEvent e) {

    try {

        repaint();


    }
    catch(NumberFormatException err) {

        JOptionPane.showMessageDialog(null, "something went wrong! heeft u wel    een waarde opgegeven?");

    }

}
</code></pre>
