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Primitive types, null and type conversion

Primitive types, null and conversion

Apex is statically typed: every variable has a type, and the compiler checks it.

Type	Example	Notes
Integer	42	32-bit
Long	42L	64-bit
Decimal	19.99	Use for money. Currency fields are Decimals
Double	3.14	Floating point
String	'hello'	Single quotes only
Boolean	true
Date, Datetime, Time	Date.today()
Id	'001...'	A validated 15/18-char record Id

Everything can be null

Any variable that isn't assigned is null, including Integers and Booleans. Using null in arithmetic throws a NullPointerException:

Integer bonus;          // null
Integer total = 10 + bonus; // 💥 NullPointerException

Guard with a ternary, or with the null-coalescing operator ??:

Integer safe = bonus == null ? 0 : bonus;
Integer alsoSafe = bonus ?? 0;

Converting

Integer i = Integer.valueOf('42');   // String → Integer
String s = String.valueOf(42);       // Integer → String
String t = 'XP: ' + 42;              // concatenation converts for you
Decimal d = Decimal.valueOf('19.99');

Your mission

The variables xpText and bonus already exist (Quill declared them for you). Follow the four steps in the editor. Variable names matter: Quill checks total, summary and safeBonus.