what is the difference between == operator and equals()? (with hashcode() ???)

by

the == operator determines if 2 references point to the same object.

So

 Object o1 = new Object();
 Object o2 = o1;

 o1 == o2; //true

 o2 = new Object();

 o1 == o2 // false

the Object.equals() method is “how do I determine if 2 references to objects, that are not the same object, are equal?”

If two references point to the same object, both 

o1 == o2 
o1.equals(o2)

should be true.

But if o1 and o2 are not the same object, they still might be equal logically. For any given class, equals depends on the semantics behind the object. For example, consider a class where field1 and field2 are set by the user, but field3 is computed and has a random element to its computation. It might make sense to define equals in this case to only depend on field1 and field2, and not field3. Thats why equals is necessary.

More Related Contents:

  1. What issues should be considered when overriding equals and hashCode in Java?
  2. Why do I need to override the equals and hashCode methods in Java?
  3. Best implementation for hashCode method for a collection
  4. Understanding the workings of equals and hashCode in a HashMap
  5. How should equals and hashcode be implemented when using JPA and Hibernate
  6. How to ensure hashCode() is consistent with equals()?
  7. Apache Commons equals/hashCode builder [closed]
  8. Hashcode and Equals for Hashset [duplicate]
  9. Why should I override hashCode() when I override equals() method?
  10. Should I write equals() and hashCode() methods in JPA entities?
  11. How to implement hashCode and equals method
  12. Is it possible in java make something like Comparator but for implementing custom equals() and hashCode()
  13. How default .equals and .hashCode will work for my classes?
  14. Java: Use hashCode() inside of equals() for convenience?
  15. What is x after “x = x++”?
  16. Overriding the java equals() method – not working?
  17. What is the difference between & and && in Java?
  18. How do hashCode() and identityHashCode() work at the back end?
  19. why equals() method when we have == operator? [duplicate]
  20. Is it possible to pass arithmetic operators to a method in java?
  21. Creating a “logical exclusive or” operator in Java
  22. Java Array HashCode implementation
  23. Difference between & and && in Java? [duplicate]
  24. Consistency of hashCode() on a Java string
  25. Java: What does ~ mean
  26. Why does String.hashCode() in Java have many conflicts? [closed]
  27. What does comparison being consistent with equals mean ? What can possibly happen if my class doesn’t follow this principle?
  28. Are two Java objects with same hashcodes not necessarily equal?
  29. Why are two AtomicIntegers never equal?
  30. What is the difference between += and =+?

Leave a Comment