AP CSA Unit 3.6: Object References and Pass by Reference Practice
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Unit 3, Section 3.6
Day 6 Practice • January 12, 2026
🎯 Focus: Object References
Practice Question
Consider the following class and method:
public class Point {
public int x;
public int y;
public Point(int x, int y) {
this.x = x;
this.y = y;
}
}
public static void move(Point p) {
p.x = p.x + 5;
p.y = p.y + 5;
}
// Client code:
Point pt = new Point(2, 3);
move(pt);
System.out.println(pt.x + " " + pt.y);What is printed as a result of executing the client code?
What This Tests: Section 3.6 covers passing object references to methods. When you pass an object to a method, you pass a reference to the same object—changes to the object persist after the method returns.
Key Concept: Reference vs Value
// PRIMITIVES: pass by value (copy)
int x = 5;
change(x); // x is still 5 after
// OBJECTS: pass by reference
Point pt = new Point(2, 3);
move(pt); // pt IS changed after!Step-by-Step Trace
| Step | Action | pt.x | pt.y |
|---|---|---|---|
| 1 | new Point(2, 3) | 2 | 3 |
| 2 | move(pt) - p refers to same object | 2 | 3 |
| 3 | p.x = p.x + 5 | 7 | 3 |
| 4 | p.y = p.y + 5 | 7 | 8 |
| 5 | Print pt.x + " " + pt.y | 7 8 | |
Common Mistakes
Mistake: Answer A (2 3)
This assumes objects work like primitives—that changes in the method don't affect the original. But p and pt reference the SAME object, so changes persist!
Visual Model
Think of References as Addresses
pt holds the address of a Point object
move(pt) copies that address to p
Both pt and p point to the SAME object in memory
Changing p.x changes the object that pt also references
Difficulty: Medium • Time: 3 minutes • AP Skill: 3.B - Object references
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