Where is it best to declare swing components?

Hello,
my first post! :D

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:

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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...

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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

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);
    }
}

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