Types and operators

Prereqs: fundamentals-02

Objectives 0 / 3

Name the four primitive types used most in robot code and give an example value for each
Evaluate arithmetic and comparison expressions without running them
Explain why dividing two integers in Java can silently discard the decimal

Hook

You write code to run a motor at half speed:

int speed = 1 / 2;
motor.set(speed);

The motor doesn’t move. 1 / 2 in Java is 0, not 0.5. Integer division throws away the decimal. The robot does exactly what you wrote — not what you meant.

Core concept

Key Concept

Every value in Java has a type — a declaration of what kind of data it is and what operations make sense on it. Using the wrong type produces wrong answers silently.

The four types you’ll use constantly

Type	What it holds	Example	Robot use
`int`	Whole numbers	`42`, `-7`, `0`	Loop counters, game-piece counts
`double`	Decimal numbers	`0.5`, `-1.0`, `90.3`	Motor power, angles, speeds
`boolean`	True or false	`true`, `false`	Sensor flags, mode switches
`String`	Text	`"hello"`, `"arm"`	Log messages, names

int gamePieces = 3;
double motorPower = -0.75;
boolean hasPiece = true;
String subsystemName = "intake";

Arithmetic operators

These work on int and double:

Operator	Meaning	Example	Result
`+`	Add	`3 + 2`	`5`
`-`	Subtract	`90.0 - 45.0`	`45.0`
`*`	Multiply	`0.5 * 2`	`1.0`
`/`	Divide	`10.0 / 4`	`2.5`
`%`	Remainder	`10 % 3`	`1`

⚠ Heads up

Integer division truncates. When both operands are int, Java discards the decimal: 7 / 2 → 3, not 3.5. Use 7.0 / 2 or (double) 7 / 2 when you need the fraction.

Comparison operators

These always produce a boolean:

Operator	Meaning	Example	Result
`==`	Equal	`angle == 90`	`true` or `false`
`!=`	Not equal	`count != 0`	`true` or `false`
`<`	Less than	`power < 0.5`	`true` or `false`
`>`	Greater than	`angle > 88`	`true` or `false`
`<=`	Less or equal	`speed <= 1.0`	`true` or `false`
`>=`	Greater or equal	`angle >= 0`	`true` or `false`

Logical operators

These combine boolean values:

Operator	Meaning	Example	Result
`&&`	AND (both true)	`hasPiece && armUp`	`true` only if both
`\|\|`	OR (either true)	`atMin \|\| atMax`	`true` if either
`!`	NOT (flip it)	`!hasPiece`	opposite of `hasPiece`

Robot example:

boolean readyToShoot = hasPiece && armAtTarget && driverPressed;
boolean limitHit = atTopLimit || atBottomLimit;

Interactive demo

Trace through this code. Notice how integer division and comparisons interact:

Code Tracer

1int pieces = 7;

2int slots = 2;

3int perSlot = pieces / slots;

4double exact = pieces / (double) slots;

5boolean full = pieces >= 5;

6boolean needMore = !full;

State

pieces7

slots2

perSlot–

exact–

full–

needMore–

Step through to see values update.

Press Start to begin stepping through the code.

Initial state

Try it yourself

⚡ Try it yourself

Before stepping through, predict each value:

double power = 3.0 / 4;
int count = 10 % 3;
boolean inRange = (power > 0.5) && (count < 5);

Code Tracer

1double power = 3.0 / 4;

2int count = 10 % 3;

3boolean inRange = (power > 0.5) && (count < 5);

State

power–

count–

inRange–

Step through to see values update.

Press Start to begin stepping through the code.

Initial state

⚡ Check your understanding

What does int result = 9 / 2 evaluate to?

Key takeaways

Use double for anything that can have a decimal (motor power, angles, distances).
Use int for counts and loop indices where fractions don’t make sense.
int / int always truncates — add .0 to one operand when you need precision.
Comparison operators return boolean, which is what if statements require.

Common confusions

“Why does 1 / 2 equal 0?” Java doesn’t know you want a fraction — you gave it two integers. It treats / as “how many whole times does 2 go into 1?” The answer is 0.

“When do I use = vs ==?” Single = assigns a value (angle = 90). Double == compares two values (angle == 90). Using = inside an if is a common bug Java will usually catch.

Challenge

⚡ Try it yourself

An encoder reads 1500 ticks. The maximum is 4000 ticks. Compute the position as a percentage (0.0 to 1.0) and print it. Also check: is the position past the halfway point? Print true or false.

Watch out for integer division — both values start as int.

Code EditorJavaCtrl+Enter to run

Stuck? Show hint

Use (double) ticks / maxTicks to avoid integer division. pastHalf is just position > 0.5.

What’s next

In Lesson 04, we’ll use these comparisons inside if/else chains to make the robot choose different behavior depending on sensor values.