Why won't my equals method work in this class? It's not functioning correctly

Question

Basically I want it to stop and print a message if they've already added that person to the ArrayList, but it won't do that.

Here's the method:

@Override
    public boolean equals(Object o) {
        if (this.name == ((Student)o).getName() && this.ID == ((Student)o).getID()) {
            return true;
        }
        else {
            return false;
        }
    }

And the code section it's used in:

public void addStudents() {
        Scanner keyboard = new Scanner(System.in);
        String name = "", ID = "";

        System.out.println("Welcome! Please type exit at any point to stop entering students and for the lottery to commence.\n");

        System.out.print("Student name: ");
        name = keyboard.nextLine();

        if (!name.equals("exit")) {
            System.out.print("Student ID: ");
            ID = keyboard.nextLine();
        }

        while (!name.equals("exit") && !ID.equals("exit")) {
            System.out.print("\nStudent name: ");
            name = keyboard.nextLine();

            if (!name.equals("exit")) {
                System.out.print("Student ID: ");
                ID = keyboard.nextLine();

                if (!ID.equals("exit")) {
                    boolean contains = false;

                    for (int i = 0; i < students.size(); i++) {
                        if (students.get(i).equals((new Student(name, ID)))) {
                            contains = true;
                        }
                    }

                    if (!contains) {
                        students.add(new Student(name, ID));
                    }
                    else {
                        System.out.println("You can only enter once.");
                    }
                }
            }
        }
    }

I've toiled over this for quite awhile, but can't put my finger on why it won't work.

See also [this post](http://stackoverflow.com/questions/513832/how-do-i-compare-strings-in-java) for a detailed explanation of how to compare strings in Java. — assylias, Oct 06 '12 at 20:01

score 1 · Accepted Answer · answered Oct 06 '12 at 19:54

1

Use the equals() method to compare strings, not ==

answered Oct 06 '12 at 19:54

Chris Gerken

16,221
6
44
59

score 1 · Answer 2 · answered Oct 06 '12 at 19:54

You should also be using String.equals in your Student.equals method:

if (this.getName().equals(((Student) o).getName()) && 
    this.getID().equals(((Student)o).getID()))

Your Student.equals uses == for String comparison, comparing object references, which will fail if the Strings are lexicographically equal, but not the same String object.

score 0 · Answer 3 · answered Oct 06 '12 at 19:54

There is problem in your equals method..

public boolean equals(Object o) {
    if (this.name == ((Student)o).getName() && this.ID == ((Student)o).getID()) {
            return true;
    }
    else {
           return false;
    }
}

You should compare name using equals() method in this also..

this.name.equals(((Student)o).getName())

And if your ID is also a String, do this for it also..

Fritz · Answer 4 · 2012-10-06T20:00:33.033

Use equals to compare names and ID's. In this case, == comparation boils down to an object comaration that will result in false since both names (each one a different String) are different objects. It will not make a literal comparation.

Just in case, since it's a name comparation you might want to use equalsIgnoreCase because, for example, John Doe is in essence the same name than john doe. Same goes for IDs if they're alphanumeric.

Why won't my equals method work in this class? It's not functioning correctly

4 Answers4