Java Pass-by-Value or Pass-by-Reference?

Java uses pass-by-value. However, the value passed for objects is a reference to the object's location in memory. This leads to confusion.

Primitives: When passing primitive types (int, float, etc.), a copy of the value is passed. Changes within the method don't affect the original variable.

public void modifyInt(int x) { x = 10; }

int y = 5;
modifyInt(y); // y remains 5

Objects: When passing objects, a copy of the reference is passed. Modifying the object's fields within the method will affect the original object.

public void modifyObject(MyClass obj) { obj.value = 10; }

MyClass myObj = new MyClass(5);
modifyObject(myObj); // myObj.value becomes 10

Key takeaway: Changes to the reference itself (e.g., reassigning obj to a new object) within a method won't affect the original reference. Only changes to the object's fields via the reference will persist. This is why it's often described as "pass-by-reference" behavior for objects, but technically, it remains pass-by-value of the reference.

Spring Boot Context: Spring Boot doesn't change this fundamental Java behavior. Dependency injection uses this object reference passing mechanism to manage bean lifecycles.