Strong Types

In constrast to Stringly typed

Instead of String username, String password, use Username username, Password password.

Switch from:

public class Profile {
    private String username;
    private String password;

    public Profile(String username, String password) { .. }
    // ..
}

to:

public class Profile {
    private Username username;
    private Password password;

    public Profile(Username username, Password password) { .. }
    // ..
}

public class Username {
    private String value;
    public boolean equals(..) { .. }
    // ..
}

public class Password {
    private String value;
    public void toString() { return "******"; }
    // ..
}

Bug Variants Addressed

• 1: Avoids argument swap by producing a compiler error.
• 5: Password.toString() never returns the true value, so a wrapping class that calls toString() on all of its member fields will not inadvertently log the password.