How to Use Java’s SuppressWarnings Annotation

import java.awt.FlowLayout;

import javax.swing.JFrame;

import javax.swing.JButton;

@SuppressWarnings("serial")

public class SimpleFrame extends JFrame {

public SimpleFrame() {

setTitle("Don't click the button!");

setLayout(new FlowLayout());

setDefaultCloseOperation(EXIT_ON_CLOSE);

add(new JButton("Panic"));

setSize(300, 100);

setVisible(true);

}

}

When you use a SuppressWarnings annotation, you tell Java not to remind you that your program contains certain questionable code. The line @SuppressWarnings("serial") tells Java not to remind you that you've omitted something called a serialVersionUID field. In other words, the SuppressWarnings annotation tells Java not to display a warning.

Without a SuppressWarnings annotation, Java warns you about a missing serialVersionUID field.

“And what,” you ask, “is a serialVersionUID field?” It’s something having to do with extending the JFrame class — something that you don’t care about. Not having a serialVersionUID field generates a warning, not an error. So live dangerously! Just suppress the warning and don’t worry about serialVersionUID fields.

• In JShell, type the following sequence of declarations and statements. What happens? Why?

jshell> JFrame frame

jshell> frame.setSize(100, 100)

jshell> frame = new JFrame()

jshell> frame.setSize(100, 100)

jshell> frame.setVisible(true)

Change the statement

setLayout(new FlowLayout());

• to

What difference does this change make when you run the program?