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I have two classes Person and Teacher. In the Person class I check if the two objects passed in are equal using the compareTo method. In the Teacher class, the problem I'm working on states that I need to override the equals method in Person. In this equals method, the only way it would return true is if it's equal in both the equals method in Person and Teacher. My question is, when I check in the Teacher's equals method, do I just call super.equals(other) in order to check if the two objects are equal by the parent class or is there something else I need to do?

Person:

public class Person implements Comparable<Person> {


    public boolean equals(Object other) {
        try {
            return this.compareTo(other) == 0;
        }catch(Exception e) {
            return false;
        }
    }
}

Teacher

public class Teacher extends Person {
    private String facultyID;
    @Override
    public boolean equals(Object other) {
        boolean personEquals = super.equals(other);
        try {
            Teacher teach1 = (Teacher)other;
            boolean idEquals = this.facultyID.equals(teach1.facultyID);
            if(idEquals && personEquals)
                return true;
            return false;
        }catch(Exception e) {
            return false;
        }
    }
}

解决方案

Basically, the contract of Object#equals states:

It is symmetric: for any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true

And the implementation of Teacher#equals doesn't meet this requirement. For cases when implementing equals method in a class that inherits from another that is not Object e.g. Teacher, you should verify if the type of the object to be compared is the same as the class you're comparing. To achieve this, you should use getClass().equals:

public class Teacher extends Person {
    private String facultyID;
    @Override
    public boolean equals(Object other) {
        //this line is nonsense, not all Persons are Teachers
        //boolean personEquals = super.equals(other);

        //avoid using try-catch
        //try {

        //verify that the other object is not null
        if (other == null) {
            return false;
        }

        //verify that the other object is specifically a Teacher, not a super or a subclass of it
        if (this.getClass().equals(other.getClass()) {
            //here comes the real check
            Teacher otherTeacher = (Teacher)other;
            return this.facultyID.equals(otherTeacher.facultyID);
        }
        return false;
    }
}

Do similar for Person in case it should not allow comparing against subclasses of it.