Select the correct output.

class Person {
String name;
int age;

public static void main(String[] args) {
Person p = new Person();
p.name = "Trina";
updatePerson(p);
System.out.printf("%s, %d", p.name, p.age);

}

private static void updatePerson(Person p){
p = new Person();
p.age = 1;
}
}

Question

Select the correct output.

class Person {
    String name;
    int age;
    
    public static void main(String[] args) {
        Person p = new Person();
        p.name = "Trina";
        updatePerson(p);
        System.out.printf("%s, %d", p.name, p.age);
        
    }
    
    private static void updatePerson(Person p){
        p = new Person();
        p.age = 1;
    }
}

BlackTom AI · Accepted Answer

Java passes object references by value, so reassigning the parameter inside the method does not affect the caller's reference.

Relevant concepts:
- In Java, object variables hold references; when passed to a method, the reference is copied (pass-by-value of the reference).
- Reassigning the parameter inside the method changes only the local copy of the reference.
- Instance fields of a newly created object have default values: int defaults to 0, Object/String defaults to null.

Step-by-step execution and state:
1. Person p = new Person();
   - A new Person object is created on the heap. Its fields: name = null, age = 0 (default).
   - Local variable p (in main) holds a reference to this object.
2. p.name = "Trina";
   - The Person object referenced by main's p now has name = "Trina", age = 0.
3. updatePerson(p);
   - The reference in main is copied and passed into updatePerson. Call it p_param; it initially points to the same Person object (name="Trina", age=0).
4. Inside updatePerson:
   - p = new Person();
     - The local parameter p now refers to a brand-new Person object whose fields are name = null, age = 0 (defaults).
     - This reassignment does not change main's p; main's p still refers to the original Person.
   - p.age = 1;
     - This sets age = 1 on the new Person object (local only). The original Person object (main's p) remains age = 0.
5. updatePerson returns.
   - The new Person object created inside updatePerson becomes eligible for garbage collection (no references from main).
   - main's p still refers to the original Person with name = "Trina" and age = 0.
6. System.out.printf("%s, %d", p.name, p.age);
   - Prints the original object's fields: "Trina, 0".

Why the correct answer is correct:
- Because only the local copy of the reference was reassigned, the original object’s age was never modified. Its age stayed at the default 0 while name was set to "Trina".

Why other outputs would be incorrect:
- "Trina, 1" would require the method to set age on the original object (e.g., without reassigning p), which it does not.
- Any output showing a null name or different age contradicts the assignments described above.

Final confirmation: The correct output is "Trina, 0", matching the provided answer.

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