Java Comparison

Abstract

There are two interfaces provided by Java to implement object comparison logic - java.lang.Comparable<T> and java.util.Comparator<T>

	`java.lang.Comparable<T>`	`java.util.Comparator<T>`
Purpose	Insert the comparison logic into object.	Insert comparison logic into objects that don’t implement `java.lang.Comparable<T>`. Overwrite objects that do implement `java.lang.Comparable<T>` with custom comparison logic. A OOP, so we can use AWS Lambda to insert the comparison logic as first-class citizen.
Comparison Method	`int compareTo(T o1, T o2)` Negative → $o 1 < o 2$ Zero → $o 1 == o 2$ Positive → $o 1 > o 2$	`int compare(T o1, T o2)` Negative → $o 1 < o 2$ Zero → $o 1 == o 2$ Positive → $o 1 > o 2$

Important

Use Integer.compare() to compare integers to avoid overflow.

Code Example

First, we created a class Student that implements Comparable<T> that compares the Student objects based on their id
Second, we created a class AgeComparator that implements Comparator<T> that compares Student objects based on their age
Lastly, we show how Collections.Sort() uses the default comparison implemented with Comparable<T>, and how we can override it with comparison logic implemented with Comparator<T>

Important

Since Comparator<T> is a Functional Interface, we can make use of Java Lambda to create a custom comparator in one line, as shown in the code editor above!