The PreTeXt Guide

<program language="java" line-numbers="yes" highlight-lines="2,6-8">
    <title>"hi" in Java</title>
    <code>
    import javax.swing.JFrame;  //Importing class JFrame
    import javax.swing.JLabel;  //Importing class JLabel
    public class HelloWorld {
        public static void main(String[] args) {
            JFrame frame = new JFrame();           //Creating frame
            frame.setTitle("Hi!");                 //Setting title frame
            frame.add(new JLabel("Hello, world!"));//Adding text to frame
            frame.pack();                          //Setting size to smallest
            frame.setLocationRelativeTo(null);     //Centering frame
            frame.setVisible(true);                //Showing frame
        }
    }
    </code>
</program>

<program interactive="activecode" language="python" label="program-activecode-python-ambles">
    <preamble>
    def add(a, b):
    </preamble>
    <code>
        # TODO - complete the add function

    </code>
    <postamble>
    # Use the function
    result = add(2, 3)
    if result == 5:
        print("Test passed")
    else:
        print("Test failed")
    </postamble>
</program>