Question

I want to override “public boolean equals(Object obj)” function, for name and age, in my class named MyObject whose structure is given below

public class MyObject{
       private String name;
       private int age;
}

How can i ?

@balusC :

What about this ?

vo  = new MyObject() {
                    public boolean equals(Object obj) {
                        return ((MyObject)obj).name().equals(this.getName());

                    }


vo  = new MyObject() {
                    public boolean equals(Object obj) {
                        return ((MyObject)obj).age() == (this.getAge());

Answer 1

Your question is a bit vague, but if the sole purpose is to have different sorting algorithms depending on what property you’d like to use, then rather use a Comparator.

public class Person {
    private String name;
    private int age;

    public static Comparator COMPARE_BY_NAME = new Comparator<Person>() {
        public int compare(Person one, Person other) {
            return one.name.compareTo(other.name);
        }
    }

    public static Comparator COMPARE_BY_AGE = new Comparator<Person>() {
        public int compare(Person one, Person other) {
            return one.age > other.age ? 1
                 : one.age < other.age ? -1
                 : 0; // Maybe compare by name here? I.e. if same age, then order by name instead.
        }
    }

    // Add/generate getters/setters/equals()/hashCode()/toString()
}

which you can use as follows:

List<Person> persons = createItSomehow();

Collections.sort(persons, Person.COMPARE_BY_NAME);
System.out.println(persons); // Ordered by name.

Collections.sort(persons, Person.COMPARE_BY_AGE);
System.out.println(persons); // Ordered by age.

As to the actual equals() implementation, I’d rather let it return true when the both Person objects are techically or naturally identical. You can use either a DB-generated PK for this to compare on technical identity:

public class Person {
    private Long id;

    public boolean equals(Object object) {
        return (object instanceof Person) && (id != null) 
             ? id.equals(((Person) object).id) 
             : (object == this);
    }
}

or just compare every property to compare on natural identity:

public class Person {
    private String name;
    private int age;

    public boolean equals(Object object) {
        // Basic checks.
        if (object == this) return true;
        if (object == null || getClass() != object.getClass()) return false;

        // Property checks.
        Person other = (Person) object;
        if (name == null ? other.name != null : !name.equals(other.name)) return false;
        if (age != other.age) return false;

        // All passed.
        return true;
    }
}

Don’t forget to override hashCode() as well when you override equals().

See also:

• Object ordering
• Sorting an ArrayList of objects
• Overriding equals() and hashCode()