This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
The "==" operator should be used for primitive types only. If it's used with objects the value compared is the reference to the object which can give you results that your not expecting. I find this a hard oncept to understand but there are numerous references that have info about it. Check RHE, examcram or the JLS. Mock exam ques. about the difference between the two are numerous and can be quite tricky.
== does plain reference comparison. It is an operator. equals() is a method defined in java.lang.Object class. Subclasses can override this method to provide a meaningful content comparison. The default behaviour implemented by the Object class does nothing but reference comparison. So, if a class doesnot override equals() method, the result of calling this method will be consistent with the results obtained when you use the == operator. CompareTo() is a method defined by the java.lang.Comparable interface. Unlike the equals() method, this method is designed to be used for determining the natural order of objects while sorting. Java provides various sorting helper classes and method and some of them call the compareTo() method( if implemented by your class ) to findout the natural sorting order of each object that is an instance of your class. So, compareTo() does not check equality, but checks which object comes first when they need to be sorted in a specific order. Ajith
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