Primitive parameters

Learn to pass primitive parameters.

Primitive type parameters

When you pass primitive types (int, double, boolean...) as method parameters, a copy of the value goes into the method. This is called pass by value.

static void doubleIt(int x) {
  x = x * 2;
}
int n = 5;
doubleIt(n);
// n is still 5

Even if you change x inside the method, the original n is not affected. Because x is a separate copy of n. This behavior prevents unexpected side effects.

Consequence of pass by value

A method with a primitive parameter cannot change the caller's variable. This makes code easier to follow: knowing what the method does is enough; it will not break the outside.

static void zero(int v) {
  v = 0;
}
int n = 9;
zero(n);
System.out.println(n);
// prints 9

If you want a method to change an outside value, you must either pass an array or object, or use the return value. With a primitive, this is not possible.

Exercise Square root approximation

Define a static double method called approxSqrt; parameter int n, body return Math.sqrt(n);. Call approxSqrt(16) from main and print the result.

Show example solution

static double approxSqrt(int n) {
  return Math.sqrt(n);
}
// inside main:
System.out.println(approxSqrt(16));

Test yourself

Match type to example

int

42
double

3.14
boolean

true
char

'A'

Fill in the blank: primitive parameter

static void half(____ x) {
  System.out.println(x / 2);
}

Show answer

static void half(int x) {
  System.out.println(x / 2);
}

What is the value of n after calling doubleIt(n)?
```
static void doubleIt(int x) {
  x = x * 2;
}
int n = 5;
doubleIt(n);
```
- It doubles
- It stays the same (pass by value)
- It is zeroed
- It throws an error
Show answer

It stays the same (pass by value) — The copy of the primitive parameter changes; the original is untouched.

Next lesson: Object parameters

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