Overriding methods
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To override the equals() method: 1. Do null and type checks 2. Type cast objects and compare individual attributes starting with numeric ones using short-circuit logic 3. Both equals() and hashCode() should be overridden together for collections to work properly 4. Override toString() to print objects in a custom format
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Overriding methods
- 2. Steps to override equals() ● Do this check -- if yes then return true. ● Do null check -- if yes then return false. ● Do the instanceof check, if instanceof return false than return false from equals in Java ,we can use getClass() method for type identification because instanceof check returns true for subclass also. if((obj == null) || (obj.getClass() != this.getClass())) return false; ● Type cast the object; note the sequence instanceof check must be prior to casting object. ● Compare individual attribute starting with numeric attribute because comparing numeric attribute is fast and use short circuit operator for combining checks.
- 3. Sample code
- 4. Cont'd
- 5. Overriding hashCode() ● Both equal() and hashCode() belong to Object class. ● It is not always necessary to override hashcode and equals. ● But if you think you need to override one, then you need to override both of them. ● We must overload hashCode() when equals() is overrided because to access the collection class effectively without violating the rules.
- 6. Example code for overriding hashCode()
- 7. Cont'd
- 8. output
- 9. Overridding toString() Reason to override toString() ● It is useful in printing the object in the format what we need.
- 10. Example code to override toString()
- 11. Sample output