Layout Question

[vittoire]

Hi. im new to the java world. i would like to enquire if it is possible to hav a gridlayout in another gridlayout. for example. i add a grid of 1,2 into the borderlayout. is it possible that i insert another grid into the grid?

example
jp1.add(jp2);

is this possible?

[dlorde]

If you set a grid layout in a panel, you can add that panel to another panel that has a grid layout, effectively nesting them.

[vittoire]

Thanks for the reply & sorry for my late reply. i did the code but i found that there is something wrong with my code. i could compile but the gui does not appear. can someone help me see what is wrong with my code & direct me please. the error happens on jp3.add(jlProcess);. Thanks in advance.

/**
* @(#)CpuGenerate.java
*
*
* @author
* @version 1.00 2010/1/13
*/


import javax.swing.*;
import java.awt.*;

public class CpuGenerate extends JFrame{

JButton jbBack, jbReset, jbGenerate, jbNext;
JLabel jlProcess, jlArrival, jlPriority, jlBurst, jl1, jl2, jl3;
JSpinner jsProcess, jsArrival1, jsArrival2, jsPriority1, jsPriority2, jsBurst1, jsBurst2;
JCheckBox jcbEnable;
JPanel jp1, jp2, jp3, jp4, jp5, jp6;

public CpuGenerate() {

setSize(800,600);

setTitle("CPU Scheduling");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

setLayout(new BorderLayout());

//initialize panels
jp1= new JPanel();
jp2= new JPanel();
jp3= new JPanel();
jp4= new JPanel();
jp5= new JPanel();
jp6= new JPanel();

//set panel layout
jp1.setLayout(new GridLayout(1,2));
jp2.setLayout(new GridLayout(3,1));
jp3.setLayout(new GridLayout(1,2));
jp4.setLayout(new GridLayout(4,4));
jp5.setLayout(new GridLayout(1,3));
jp6.setLayout(new FlowLayout());

//add panels to frame
add(jp1, BorderLayout.CENTER);
/* add(jp2, BorderLayout.NORTH);
add(jp3, BorderLayout.WEST);
add(jp4, BorderLayout.SOUTH);
add(jp5, BorderLayout.EAST);*/
jp1.add(jp2);
jp1.add(jp6);
jp2.add(jp3);
jp2.add(jp4);
jp2.add(jp5);

//add components into panel
jp3.add(jlProcess);
jp3.add(jsProcess);
jp4.add(jlArrival);
jp4.add(jsArrival1);
jp4.add(jl1);
jp4.add(jsArrival2);
jp4.add(jlPriority);
jp4.add(jsPriority1);
jp4.add(jl2);
jp4.add(jsPriority2);
jp4.add(jcbEnable);
jp4.add(jlBurst);
jp4.add(jsBurst1);
jp4.add(jl3);
jp4.add(jsBurst2);
jp5.add(jbBack);
jp5.add(jbReset);
jp5.add(jbNext);
jp6.add(jbNext);

// Create spinner
JSpinner jsProcess = new JSpinner();
JSpinner jsArrival1 = new JSpinner();
JSpinner jsArrival2 = new JSpinner();
JSpinner jsPriority1 = new JSpinner();
JSpinner jsPriority2 = new JSpinner();
JSpinner jsBurst1 = new JSpinner();
JSpinner jsBurst2 = new JSpinner();

//Create Buttons
jbBack = new JButton("Back");
jbReset = new JButton("Reset");
jbGenerate = new JButton("Generate");
jbNext = new JButton("Next");

//Create label
jlProcess = new JLabel("No. Of Process:");
jlArrival = new JLabel("Arrival Time:");
jlPriority = new JLabel("Priority:");
jlBurst = new JLabel("Burst Time:");
jl1 = new JLabel("To");
jl2 = new JLabel("To");
jl3 = new JLabel("To");

//create combobox
jcbEnable = new JCheckBox("Enable");



// Set spinner value
jsProcess.setValue(new Integer(1));
jsArrival1.setValue(new Integer(1));
jsArrival2.setValue(new Integer(2));
jsPriority1.setValue(new Integer(1));
jsPriority2.setValue(new Integer(2));
jsBurst1.setValue(new Integer(1));
jsBurst2.setValue(new Integer(2));



setVisible(true);

}

public static void main(String[] args)
{


JFrame.setDefaultLookAndFeelDecorated(true);
CpuGenerate frame = new CpuGenerate();
}

}

[r035198x]

1.) Use code tags when posting code
2.) Did you check the console for error messages/exceptions? You should be getting a Nullpointer on jp3.add(jlProcess); because jlProcess will be null at that point.

[vittoire]

Hi, sorry im quite new here. so i didnt know that im suppose to use code tags when posting my codes.

im quite confused about the checking console for error messages. Do you mind explaining about the nullpointer?

the error i gt was

Exception in thread "main" java.lang.NullPointerException
at java.awt.Container.addImpl(Container.java:1041)
at java.awt.Container.add(Container.java:365)
at CpuGenerate.<init>(CpuGenerate.java:59)
at CpuGenerate.main(CpuGenerate.java:128)

[dlorde]

Do you mind explaining about the nullpointer?

You can't add the components to the container until you've initialised them. jlProcess is null until you initialise it with a new JLabel. If you try to use it before it has been initialised, for example by adding it to a panel, you'll get a NullPointerException.

[vittoire]

Thanks alot dlorde and r035198x. i realise what my mistakes were.