Scratch → Java cheat sheet

Which Java line replaces which block. Inside a sprite or stage class, every method is called on this: move (10) steps becomes this.move(10);. Each line ends with a semicolon. Look a method up in the documentation to see the block, an explanation and an example you can run.

Events

Scratch	Java
when green flag clicked (setting up)	the constructor: public Cat() { ... }
when green flag clicked + forever	public void run() { ... }
when [space] key pressed	public void whenKeyPressed(KeyCode key) { if (key == KeyCode.SPACE) { ... } }
when this sprite clicked	public void whenClicked() { ... }
when stage clicked	in the stage: public void whenMouseClicked(MouseCode button) { ... }
when backdrop switches to [night]	public void whenBackdropSwitches(String name) { if (name.equals("night")) { ... } }
broadcast [start]	this.broadcast("start");
when I receive [start]	public void whenIReceive(String message) { if (message.equals("start")) { ... } }

Motion

Scratch	Java
move (10) steps	this.move(10);
turn ↻ (15) degrees	this.turnRight(15);
turn ↺ (15) degrees	this.turnLeft(15);
go to x: (0) y: (0)	this.setPosition(0, 0);
go to [random position]	this.goToRandomPosition();
go to [mouse-pointer]	this.goToMousePointer();
glide (1) secs to x: (100) y: (0)	this.glide(1, 100, 0);
point in direction (90)	this.setDirection(90);
point towards [mouse-pointer]	this.pointTowardsMousePointer();
change x by (10)	this.changeX(10);
set x to (0)	this.setX(0);
change y by (10)	this.changeY(10);
set y to (0)	this.setY(0);
if on edge, bounce	this.ifOnEdgeBounce();
set rotation style [left-right]	this.setRotationStyle(RotationStyle.LEFT_RIGHT);
(x position), (y position), (direction)	this.getX(), this.getY(), this.getDirection()

Looks

Scratch	Java
say [Hello!] for (2) seconds	this.say("Hello!", 2000);
say [Hello!]	this.say("Hello!");
think [Hmm...]	this.think("Hmm...");
(adding a costume)	in the constructor: this.addCostume("bunny1_stand");
switch costume to [bunny1_jump]	this.switchCostume("bunny1_jump");
next costume	this.nextCostume();
(adding a backdrop)	in the stage's constructor: this.addBackdrop("background");
switch backdrop to [night]	in the stage: this.switchBackdrop("night");
next backdrop	in the stage: this.nextBackdrop();
change size by (10)	this.changeSize(10);
set size to (50) %	this.setSize(50);
change [color] effect by (25)	this.changeTint(25);
set [ghost] effect to (50)	this.setTransparency(50);
show / hide	this.show(); / this.hide();
go to [front] layer	this.goToFrontLayer();
(costume [name]), (size)	this.getCurrentCostumeName(), this.getSize()

Sound

Scratch	Java
(adding a sound)	in the constructor: this.addSound("handleCoins");
start sound [handleCoins]	this.playSound("handleCoins");
stop all sounds	this.stopAllSounds();
set volume to (50) %	this.setVolume(50);
change volume by (-10)	this.changeVolume(-10);

Control

Scratch	Java
forever	run() is already repeated, see Differences to Scratch
wait (1) seconds	if (this.getTimer().everyMillis(1000)) { ... } inside run()
repeat (10)	for (int i = 0; i < 10; i++) { ... }
if <> then	if (...) { ... }
if <> then … else	if (...) { ... } else { ... }
wait until <>	if (...) { ... } inside run(): it is checked again every frame
repeat until <>	while (!...) { ... }, but never inside run(). Usually an if in run() is what you want.
stop [all]	Window.getInstance().exit();
create clone of [myself]	this.clone();
when I start as a clone	public void whenStartsAsClone() { ... }
delete this clone	this.deleteThisClone();

Sensing

Scratch	Java
<touching [Coin]?>	this.isTouchingSprite(Coin.class)
<touching [mouse-pointer]?>	this.isTouchingMousePointer()
<touching [edge]?>	this.isTouchingEdge()
(distance to [mouse-pointer])	this.distanceToMousePointer()
ask [What's your name?] and wait	this.ask("What's your name?"); and wait for this.isAsking() to become false
(answer)	this.getAnswer()
<key [space] pressed?>	this.isKeyPressed(KeyCode.SPACE)
<mouse down?>	this.isMouseDown()
(mouse x), (mouse y)	this.getMouseX(), this.getMouseY()
(timer)	Timer.millis()
reset timer	this.getTimer().reset();, then this.getTimer().afterMillis(30000) is true after 30 seconds

Operators

Scratch	Java
(a + b), (a - b), (a * b), (a / b)	a + b, a - b, a * b, a / b (careful: 7 / 2 is 3, but 7.0 / 2 is 3.5)
(pick random (1) to (10))	this.pickRandom(1, 10)
b>, <a < b>	a > b, a < b
<a = b> for numbers	a == b
<a = b> for text	a.equals(b)
<<> and <>>, <<> or <>>, <not <>>	... && ..., ... || ..., !...
(join [Hello ] [world])	"Hello " + "world"
(letter (1) of [apple])	"apple".charAt(0): Java counts from 0
(length of [apple])	"apple".length()
<[apple] contains [a]?>	"apple".contains("a")
(a mod b)	a % b
(round (2.6))	Operators.round(2.6)
([sqrt] of (9))	Operators.sqrtOf(9)

Variables

A variable for one sprite goes at the top of its class. A variable for all sprites goes into the stage. Differences to Scratch shows both.

Scratch	Java
make a variable [score]	private int score = 0; at the top of the class (int for whole numbers, double for decimals, String for text, boolean for true/false)
set [score] to (0)	this.score = 0;
change [score] by (1)	this.score = this.score + 1;
show variable [score]	this.showVariable("score", () -> this.score);
make a list [names]	private ArrayList<String> names = new ArrayList<>(); with import java.util.ArrayList;
add [Ada] to [names]	this.names.add("Ada");
(item (1) of [names])	this.names.get(0): counting starts at 0
(length of [names])	this.names.size()

Pen

Every sprite has a pen of its own, which draws wherever the sprite goes.

Scratch	Java
pen down / pen up	this.getPen().down(); / this.getPen().up();
set pen size to (5)	this.getPen().setSize(5);
erase all	in the stage: this.eraseAll();
stamp	this.stamp();