Where is it best to declare swing components?

[MacNstuff]

Hello,
my first post!

Can someone please explain to me the implications of declaring components inside the class constructor verses outside it?

For example, declaring the components outside the constructor seems to be common:

Code:

import javax.swing.*;
class mytest {
JLabel alabel;
JCheckBox acheckbox;

mytest() {
JFrame myf = new JFrame("Hello World");
myf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
alabel = new JLabel("Just some text");
acheckbox = new JCheckBox("Some random option");
myf.add(alabel); myf.add(acheckbox);
myf.setVisible(true);
}
// ... create frame etc...

but I've also seen the components created inside the constructor too:

Code:

import javax.swing.*;
class mytest {

mytest() {
JFrame myf = new JFrame("Hello World");
myf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JLabel alabel = new JLabel("Just some text");
JCheckBox acheckbox = new JCheckBox("Some random option");
myf.add(alabel); myf.add(acheckbox);
myf.setVisible(true);

Now I'm guessing the reason is something to do with the scope of the component - ie making it accessible from another class (in another file), but thats just my guess. Can someone explain this to me please?

Thx
M

[hardwired]

Code:

import javax.swing.*;

class MyTest {
    // If another method (outside the constructor) needs to
    // see/access these then they will need to be declared
    // here as member variables in class scope.
    // Otherwise it is considered good practive to hide them
    // as local variables. The less you expose the better.
    JLabel alabel;
    JCheckBox acheckbox;

    MyTest() {
        // initialize components
        alabel = new JLabel("Just some text");
        acheckbox = new JCheckBox("Some random option");
        // ... create frame etc...
        JFrame myf = new JFrame("Hello World");
        myf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        System.out.println("JFrame default layout manager = " +
                            myf.getLayout().getClass().getName());
        // Use constraints to add components. No constraint adds
        // the component to the center section by default: so
        // you'll only see the last component added.
        myf.add(alabel, BorderLayout.NORTH);
        myf.add(acheckbox, BorderLayout.SOUTH);
/*
        // Or, you can add both components to a JPanel
        // (FlowLayout default) and add it to a section
        // in the BorderLayout. Many options like this...
        JPanel panel = new JPanel();
        panel.add(alabel);
        panel.add(acheckbox);
        myf.add(panel, BorderLayout.NORTH);
*/
        myf.setVisible(true);
    }
}