How to run a java applet code

I have never run a Java code and I want to run the code I am going to post below. So can someone tell me how I can run the code on Ubuntu including what things I should install?

I also want to modify it and put a heart image on the guy's chest and write I LOVE YOU. Can anyone help me with that as well?

import java.awt.*;
import java.applet.*;

public class FunnyClown extends Applet {

    public void init() {
    }

    public void paint(Graphics g) {

        g.drawString("See!  A Funny Clown=)", 30, 30 );

        //Draw a beautiful sky
        setBackground(Color.cyan);

         //Grass
        g.setColor(Color.green);
        g.fillRect(0,580,1500,3000);

        //Draw a round face
        g.setColor(Color.white);
        g.fillArc(555,300,140,150,0,360);

        //Eyes
        g.setColor(Color.black);
        g.fillArc(600,360,15,20,0,360);
        g.fillArc(640,360,15,20,0,360);

        //Smile
        g.setColor(Color.red);
        g.drawArc(615,420,20,8,190,200);

        //Hat
        g.setColor(Color.pink);
        g.fillArc(520,290,205,60,0,360);
        g.fillRect(568,220,115,100);
        g.fillArc(568,200,115,50,0,360);

        //Ribbons
        g.setColor(Color.white);
        g.fillRect(568,285,115,15);

        //Body
        g.setColor(Color.white);
        g.fillRect(543,470,25,70);
        g.fillRect(683,470,25,70);
        g.fillArc(543,535,20,25,0,360);
        g.fillArc(685,535,20,25,0,360);

        //T-shirt
        g.setColor(Color.yellow);
        g.fillRect(570,450,110,200);
        int []x1={570,500,570};
        int []y1={450,475,490};
        g.fillPolygon(x1,y1,3);
        int []x2={680,750,680};
        int []y2={450,475,490};
        g.fillPolygon(x2,y2,3);

        //Pants
        g.setColor(Color.blue);
        g.fillRect(570,580,110,150);
        g.setColor(Color.green);
        int []x3={625,598,638};
        int []y3={600,730,730};
        g.fillPolygon(x3,y3,3);

        //Shoes
        g.setColor(Color.black);
        g.fillArc(570,728,35,30,0,360);
        g.fillArc(642,728,35,30,0,360);

        //Clouds
        g.setColor(Color.white);
        g.fillArc(100,100,60,60,0,360);
        g.fillArc(120,120,70,70,0,360);
        g.fillArc(120,80,70,70,0,360);
        g.fillArc(160,70,80,80,0,360);
        g.fillArc(190,75,90,90,0,360);
        g.fillArc(240,85,60,60,0,360);
        g.fillArc(220,110,70,70,0,360);
        g.fillArc(170,120,70,70,0,360);

        //Sun
        g.setColor(Color.yellow);
        int x[]={900,1080,1180,980,1080,1180,800,900,1000};
        int y[]={100,80,150,80,100,80,110,100,60};
        g.fillPolygon(x,y,9);
        g.setColor(Color.red);
        g.fillArc(1015,50,80,80,0,360);

        //Flower
        g.setColor(Color.magenta);
        g.fillArc(80,500,20,20,0,360);
        g.fillArc(95,485,20,20,0,360);
        g.fillArc(110,500,20,20,0,360);
        g.fillArc(86,515,20,20,0,360);
        g.fillArc(103,515,20,20,0,360);
        g.setColor(Color.yellow);
        g.fillArc(95,503,20,20,0,360);
        g.setColor(Color.darkGray);
        g.fillRect(103,525,5,70);

        g.setColor(Color.magenta);
        g.fillArc(300,500,20,20,0,360);
        g.fillArc(315,485,20,20,0,360);
        g.fillArc(330,500,20,20,0,360);
        g.fillArc(306,515,20,20,0,360);
        g.fillArc(323,515,20,20,0,360);
        g.setColor(Color.yellow);
        g.fillArc(315,503,20,20,0,360);
        g.setColor(Color.darkGray);
        g.fillRect(323,525,5,70);

        g.setColor(Color.magenta);
        g.fillArc(190,500,20,20,0,360);
        g.fillArc(205,485,20,20,0,360);
        g.fillArc(220,500,20,20,0,360);
        g.fillArc(196,515,20,20,0,360);
        g.fillArc(217,515,20,20,0,360);
        g.setColor(Color.yellow);
        g.fillArc(205,503,20,20,0,360);
        g.setColor(Color.darkGray);
        g.fillRect(215,525,5,70);

        //House
        g.setColor(Color.gray);
        int []x4={850,1050,1250};
        int []y4={300,200,300};
        g.fillPolygon(x4,y4,3);
        g.setColor(Color.lightGray);
        g.fillRect(850,300,400,300);


        //Window
        g.setColor(Color.cyan);
        g.drawRect(1100,350,100,100);
        g.drawLine(1100,400,1200,400);
        g.drawLine(1150,350,1150,450);

        //Door
        g.setColor(Color.darkGray);
        g.fillRect(900,400,130,200);
        g.setColor(Color.yellow);
        g.fillArc(930,480,10,10,0,360);





    }
}

Here's what the code supposed to show when you run it:

Solution

To draw the I love you text you can call: g.drawString(...) method and position it over the T-Shirt.

Next to draw a heart shape, you can call the same method using the ASCII's heart shape: ♥

But be sure to use a nice (big enough) font so it can be visualized correctly, for example:

g.setFont(new Font("Verdana", Font.PLAIN, 25));
g.setColor(Color.BLACK);
g.drawString("I love you", 570, 480);

g.setColor(Color.RED);
g.drawString("♥", 620, 510);

But as you've been said, Java Applets are no longer supported by browsers, there are 2 things you can do:

Convert the code into a Swing Application (recommended)
Use AppletViewer (Which I've never used)

We're going to go through the 1st one:

First, we need to change:

// Draw a beautiful sky
setBackground(Color.cyan);

for:

g.setColor(Color.CYAN);
g.fillRect(0, 0, 1500, 1000); //I'm lazy to search the window size... change it accordingly

Next, we need to remove extends Applet from our class and change it to extends JPanel and change

public void paint(Graphics g) {

To:

@Override
public void paintComponent(Graphics g) {

And add another overriden method:

@Override
public Dimension getPreferredSize() {
    return new Dimension(1500, 1000); //Again, change it to the window's correct size.
}

To finish we need to create a main method as follows:

private JFrame frame;

public static void main(String[] args) {
    SwingUtilities.invokeLater(new FunnyClown()::createAndShowGui);
}

private void createAndShowGui() {
    frame = new JFrame(getClass().getSimpleName());

    this.setOpaque(true);
    frame.add(this);
    frame.pack();
    frame.setVisible(true);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}

Now, if you run the application you should see something like this:

For reference, you're going to need:

Java 8+ JDK installed (Oracle preferred): See How to install Java with apt-get on ubuntu
A Java IDE (I recommend you Eclipse) for the next point
How to create a Runnable Jar in Eclipse and Create executable Jar file under Eclipse. This way all you will need is to double-click the file to run it.