Walk though the execution of the equals() method in class User for a few well-chosen objects as the parameter

Homework Help: Questions and Answers: Walk though the execution of the equals() method in class User for a few well-chosen objects as the parameter. What happens at each point in the execution?

Answer:

To walk through the execution of the equals() method in the User class, let’s first assume what the User class might look like. A common structure for such a class includes fields like username, email, and id, and the equals() method is often overridden to compare these fields to determine if two User objects are equal.

Here’s a simple example of what the User class might look like in Java:

    public class User {
    private String username;
    private String email;
    private int id;

    public User(String username, String email, int id) {
        this.username = username;
        this.email = email;
        this.id = id;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null || getClass() != obj.getClass()) {
            return false;
        }
        User user = (User) obj;
        return id == user.id &&
               username.equals(user.username) &&
               email.equals(user.email);
    }

    // Additional methods like getters, hashCode, etc.
}

Step-by-Step Execution of the equals() Method

Let’s consider three objects and walk through the execution of the equals() method with them:

User user1 = new User("alice", "[email protected]", 1);
User user2 = new User("alice", "[email protected]", 1);
User user3 = new User("bob", "[email protected]", 2);

Now, let’s walk through the execution for user1.equals(user2) and user1.equals(user3).

Case 1: user1.equals(user2)

Method Invocation:
- user1.equals(user2) is called.
Check Reference Equality:
- if (this == obj) checks if user1 and user2 refer to the same object in memory.
- In this case, they are different objects, so the check returns false, and the execution moves to the next condition.
Null Check and Class Check:
- if (obj == null || getClass() != obj.getClass()) checks if user2 is null or if user1 and user2 are instances of different classes.
- user2 is not null, and both user1 and user2 are instances of the User class, so this check returns false, and execution continues.
Cast to User:
- User user = (User) obj; casts user2 to a User object. This cast is safe because the class check passed.
Field Comparisons:
- return id == user.id && username.equals(user.username) && email.equals(user.email); compares the id, username, and email fields of user1 and user2.
- Since both objects have the same id, username, and email, the method returns true.

Case 2: user1.equals(user3)

Method Invocation:
- user1.equals(user3) is called.
Check Reference Equality:
- if (this == obj) checks if user1 and user3 refer to the same object in memory.
- They are different objects, so the check returns false, and execution moves to the next condition.
Null Check and Class Check:
- if (obj == null || getClass() != obj.getClass()) checks if user3 is null or if user1 and user3 are instances of different classes.
- user3 is not null, and both user1 and user3 are instances of the User class, so this check returns false, and execution continues.
Cast to User:
- User user = (User) obj; casts user3 to a User object. This cast is safe because the class check passed.
Field Comparisons:
- return id == user.id && username.equals(user.username) && email.equals(user.email); compares the id, username, and email fields of user1 and user3.
- The id fields are different (1 vs. 2), so the comparison returns false without needing to check the other fields.