1 · Foundations · lesson 3 of 41

Variables & Primitive Types

Eight primitive types, one reference world, and why the difference matters.

Java has 8 primitive types stored directly on the call stack, and reference types whose values live on the heap while a reference to them sits on the stack.

Java
int      age    = 27;          // 32-bit integer
long     views  = 9_000_000L;  // 64-bit integer
double   pi     = 3.14159;     // 64-bit float
float    ratio  = 0.5f;        // 32-bit float
boolean  ready  = true;
char     grade  = 'A';
byte     flag   = 0x1F;
short    port   = 8080;

String   name   = "Ada";       // reference type
TIP
The 3D visualization shows stack frames on the left with primitives inline, and objects on the heap with arrows from stack references.
Loading 3D scene…
Key takeaways
  • ✓8 primitives: byte, short, int, long, float, double, boolean, char.
  • ✓Primitives store the value; references store an address to a heap object.
  • ✓Use _ as a digit separator for readable large numbers.
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