Java Comparison

Abstract

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• 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 → $o1<o2$ Zero → $o1==o2$ Positive → $o1>o2$	int compare(T o1, T o2) Negative → $o1<o2$ Zero → $o1==o2$ Positive → $o1>o2$

Important

Use Integer.compare() to compare integers to avoid overflow. For more information, refer to Java docs.

Code Example

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• 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!