Why do I need a brace after my serialVersionUID?

Question

I had a syntax error one the line with the serialVersionUID. to fix this error i had to place a bracket at the end of that line and close it at the end of my code... my question is Why? There was no need for this in the file that contains the Jframe... also what is serialVersionUID? I apologize if my questions seem elementary, I'm new to Programming, newer to java, and this is my 3ed day on GUI's.

import javax.swing.*;


public class HangmanPanel extends JPanel{
    private static final long serialVersionUID = -1767262708330188227L;{

    this.setLayout(null);
    JLabel heading = new JLabel("Welcome to the Hangman App");
    JButton Button = new JButton("Ok");
    //get input

    JLabel tfLable = new JLabel("Please Enter a Letter:");
    JTextField text = new JTextField(10);


    heading.setSize(200, 50);
    tfLable.setSize(150, 50);
    text.setSize(50, 30);
    Button.setSize(60, 20);


    heading.setLocation(300, 10);
    tfLable.setLocation(50, 40);
    text.setLocation(50, 80);
    Button.setLocation(100, 85);

    this.add(heading);
    this.add(tfLable);
    this.add(text);
    this.add(Button);
}}

Answer 1

Your problem has nothing to do with serialVersionUID. Go ahead, delete that entire line; you'll see that you still need the braces.

Your problem is that you're writing code outside of any function. Therefore, Java considers it to be an instance initializer, and instance initializers must be surrounded by braces.

The easiest-to-understand solution is to create a constructor to contain your code:

public class HangmanPanel extends JPanel{
    private static final long serialVersionUID = -1767262708330188227L;

    public HangmanPanel () {

        this.setLayout(null);
        JLabel heading = new JLabel("Welcome to the Hangman App");
        JButton Button = new JButton("Ok");

        // and so on

From a purely behavioral perspective, adding an explicit constructor in this case does nothing: instance initializers are invoked as part of object construction. However, they are confusing (as you've shown by your question). Adding the constructor clears up the confusion.