How to override compareTo method in Java - Example Tutorial

What is compareTo() method in Java

compareTo() method is defined in interface java.lang.Comparable and it is used to implement natural sorting on java classes. natural sorting means the the sort order which naturally applies on object e.g. lexical order for String, numeric order for Integer or Sorting employee by there ID etc. most of the java core classes including String and Integer implements CompareTo() method and provide natural sorting.

Why do you need CompareTo()

Sorting is an essential part of application development, which you often required to implement in your system. in Java sorting is implemented using Comparator and Comparable in Java. Since we store java objects in Collection there are also certain Set and Map which provides automating sorting when you insert element on that e.g. TreeSet and TreeMap. to implement sorting you need to override either compareTo(Object o) method or Comparable class or compare(Object o1, Object o2) method of Comparator class. Most of the classes implement Comparable to implement natural order. for example if you are writing Employee object you probably want to implement Comparable interface and override compareTo() method to compare current employee with other employee based on ID. So essentially you need to override compareTo() because you need to sort elements in ArrayList or any other Collection.

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