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Thread: component

  1. #1
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    Default component

     
    import java.awt.FlowLayout;
     
    import javax.swing.Box;
    import javax.swing.BoxLayout;
    import javax.swing.JCheckBox;
    import javax.swing.JComponent;
    import javax.swing.JPanel;
    import javax.swing.JTextField;
     
    public class hyperlikntest extends JComponent{
     
    	public static void main(String [] args){
     
    		Box f = new Box(BoxLayout.Y_AXIS);
    		int NumOfRperP=10;
    		JPanel[] p = new JPanel[NumOfRperP];
    		JCheckBox[] c = new JCheckBox[NumOfRperP];
    		JTextField[] t = new JTextField[NumOfRperP];
     
     
    		for (int i =0; i< NumOfRperP; i++){
    			t[i].setColumns(50);
    			p[i].setLayout(new FlowLayout(FlowLayout.LEFT));
    			p[i].add(c[i]);
    			p[i].add(t[i]);	
    			f.add(p[i]);
    		}
     
    		f.setVisible(true);
     
    	}
     
    }


  2. #2
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    Default Re: component

    noooooooo answer

  3. #3
    Administrator copeg's Avatar
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    Default Re: component

    Quote Originally Posted by nasi View Post
    noooooooo answer
    What is the question?

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    Default Re: component

    when I execute the above code it generates :

    "Exception in thread "main" java.lang.NullPointerException
    at test.hyperlikntest.main(hyperlikntest.java:29)"

    I was wondering what is the reason

  5. #5
    Administrator copeg's Avatar
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    Default Re: component

    The code creates an array, but doesn't instantiate the objects of that array

    JPanel[] panels = new JPanel[1];
    panels[0].add(new JComponent());//throws a null pointer exception because panels[0] was never instantiated
    panels[0] = new JPanel();//instantiate
    panels[0].add( new JComponent() );//now it works like a charm

  6. The Following User Says Thank You to copeg For This Useful Post:

    nasi (April 4th, 2010)

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