Differences to Scratch

Probably the most noticeable differences to Scratch are the following:

• The coordinated start in the top left hand side corner and not in the center.
• There is not wait-block on a Sprite-level, you need to use Timers.

If you want to achieve something like this inside a Sprite:

when green flag clicked
forever
next costume
wait (1) seconds

You can use a timer.

public class Cat extends Sprite {
    // executes 60-times a second, if the sprite is added to a stage.
    public void run() {
        if (this.getTimer().everyMillis(1000)) {
            this.nextCostume();
        }
    }
}

• There is no Sprite library, you have to search the internet.
• There is no Sound library, you have to search the internet.
• There are no built-in editors, you have to use external tools like GIMP, Inkscape, Audacity and so on.
• If you want to share your project with others, you have to used external sharing platforms like Nextcloud, iCloud, Dropbox or better a code sharing platform like GitHub.
• You can not use a forever loop. This will halt you program.

If you want to achieve something like this inside a Sprite:

when green flag clicked
forever
move (10) steps

You can use the run-method of the Sprite-class.

public class Cat extends Sprite {
    // executes 60-times a second, if the sprite is added to a stage.
    public void run() {
        this.move(10);
    }
}

• If you want to have a variable for all sprites, you have to use a static attribute. Static attributes are available across all objects.

public class Cat extends Sprite {
    public static int hitCounter = 1;
}
 
public class MyProgram {
    public MyProgram() {
        Cat.hitCounter += 1;
    }
}

• There are no send, broadcast or receive message methods, you need to make use of custom-methods and object-references.

public class Sender extends Sprite {
    private Receiver receiver;
 
    public Sender(Receiver aReceiver) {
        receiver = aReceiver;
    }
 
    public whenClicked() {
        aReceiver.receive("Hello");
    }
 
}
 
public class Receiver extends Sprite {
    public void receive(String text) {
        this.say(text);
    }
}
 
public class MyProgram {
    Stage myStage = new Stage();
    Receiver myReceiver = new Receiver();
    myStage.add(myReceiver);
    Sende mySender = new Sender(myReceiver);
    myStage.add(mySender);
}