Gain insights into Java Collections Framework. Delve into lists, sets, and hashmaps. Learn about data modification, sorting, thread-safety, and internal workings for efficient usage.

Collection is one of the most important topics for Java programming. Without the proper knowledge of every collection type in Java, it becomes difficult for you to decide which option to pick in a particular scenario.

This course will give you a great understanding of all collection types available in the Collections Framework like lists, linked lists, sets, and hashmaps. 

After completing this course, you will know how data can be modified within a collection, how to sort a collection, and how it can be made thread-safe. You will also cover the internal working of each Java collection so you can work with them more efficiently.

Collections in Java

# Comparable introduction

`Collections.sort()` method sorts the given List in ascending order. But the question is, how does the `sort()` method decide which element is smaller and which one is larger?

Each wrapper class(Integer, Double, or Long), String class, and Date class implements an interface called **Comparable**. This interface contains a `compareTo(T o)` method which is used by sorting methods to sort the Collection. This method returns a negative integer, zero, or a positive integer if **this** object is less than, equal to, or greater than the object passed as an argument.

> If we use the `Collections.sort(List<T> list)` method to sort an **ArrayList**, then the class whose objects are stored in the **ArrayList** must implement the Comparable interface. If the **ArrayList** stores an Integer, a Long, or a String, then we don’t need to worry as these classes already implement the Comparable interface. But if the **ArrayList** stores a custom class object, then that class must implement the Comparable interface.

In the below example, we have a custom class called `Employee`. We have stored some `Employee` objects in an **ArrayList**, and we need to sort it. The below example will not compile as the `Employee` class does not implement the Comparable interface.

Let's discuss Comparable Interface in Java.

Let's Begin

Lists in Java

LinkedList in Java

CopyOnWriteArrayList in Java

Sets in Java

TreeSet in Java

HashMap In Java

TreeMap in Java

LinkedHashMap in Java

Additional Map Implementations

Arrays Class

Collections Class

Understanding Comparable Interface

Comparable introduction