Passing parameters (pass‑by‑value)

Java is strictly pass‑by‑value. This means a copy of the argument’s value is passed to the method.

With primitive types

The method receives a copy of the value. Changes to the parameter do not affect the original.

void increment(int x) {
    x++;
}
int a = 5;
increment(a);
System.out.println(a); // still 5

With reference types

The method receives a copy of the reference (the memory address). The reference copy points to the same object.

• Changing the object’s fields affects the original object.
• Reassigning the parameter to a new object does NOT affect the original reference.

class Person { String name; }

void changeName(Person p) {
    p.name = "Bob";   // modifies original object
}

void reassign(Person p) {
    p = new Person(); // local copy now points to new object
    p.name = "Charlie";
}

Person alice = new Person();
alice.name = "Alice";
changeName(alice);
System.out.println(alice.name); // Bob

reassign(alice);
System.out.println(alice.name); // still Bob (original reference unchanged)

Key takeaway: You cannot swap two objects using a method because Java copies references, not the objects themselves.