basic work in collections, TOC, Hiearchy, Methods of Collection Interface

study/COLLECTIONS.MD

@@ -2,4 +2,46 @@
 
 Java contains many object based data structures, some sorted, some limited, some simple, some complex.
 
-Not all of them work in familiar ways, and their methods can be confusing without proper usage, study, and a quick explanation over how they're used.
+Not all of them work in familiar ways, and their methods can be confusing without proper usage, study, and a quick explanation over how they're used.
+
+This page will be using [javaTpoint](https://www.javatpoint.com/collections-in-java) for sources regarding all interfaces and classes referenced in this file.
+
+## Table of Contents
+
+<!-- TOC -->
+
+- [Collections](#collections)
+    - [Table of Contents](#table-of-contents)
+    - [Hierarchy of Collection Framework](#hierarchy-of-collection-framework)
+    - [Methods of the Collection Interface](#methods-of-the-collection-interface)
+
+<!-- /TOC -->
+
+## Hierarchy of Collection Framework
+
+All datastructures referenced here can be imported using `import java.util.<structure>;`, or just `import java.util.*;` (I recommend making more direct import statements as a 'good practice' but it does not matter in the end).
+
+[![Hierarchy of Interfaces and Classes from Collection (Iterable)](https://i.imgur.com/fifX1Ek.png)](https://static.javatpoint.com/images/java-collection-hierarchy.png)
+
+## Methods of the Collection Interface
+
+| Method                      | Description                                         |
+|-----------------------------|-----------------------------------------------------|
+| **public boolean add(E e)** | It is used to insert an element in this collection. |
+| **public boolean addAll(Collection<? extends E> c)** | It is used to insert the specified collection elements in the invoking collection. |
+| **public boolean remove(Object element)** | It is used to delete an element from the collection. || **public boolean removeAll(Collection<?> c)** | It is used to delete all the elements of the specified collection from the invoking collection. |
+| **default boolean removeIf(Predicate<? super E> filter)** | It is used to delete all the elements of the collection that satisfy the specified predicate. |
+| **public boolean retainAll(Collection<?> c)** | It is used to delete all the elements of invoking collection except the specified collection. |
+| **public int size()** | It returns the total number of elements in the collection. |
+| **public void clear()** | It removes the total number of elements from the collection. |
+| **public boolean contains(Object element)** | It is used to search an element. |
+| **public boolean containsAll(Collection<?> c)** | It is used to search the specified collection in the collection. |
+| **public Iterator iterator()** | It returns an iterator. |
+| **public Object[] toArray()** | It converts collection into array. |
+| **public <T> T[] toArray(T[] a)** | It converts collection into array. Here, the runtime type of the returned array is that of the specified array. |
+| **public boolean isEmpty()** | It checks if collection is empty. |
+| **default Stream<E> parallelStream()** | It returns a possibly parallel Stream with the collection as its source. |
+| **default Stream<E> stream()** | It returns a sequential Stream with the collection as its source. |
+| **default Spliterator<E> spliterator()** | It generates a Spliterator over the specified elements in the collection. |
+| **public boolean equals(Object element)** | It matches two collections. |
+| **public int hashCode()** | It returns the hash code number of the collection. |

study/STUDY.MD

@@ -443,7 +443,7 @@ For lists, one can use `Collections.sort` to sort any class that implements the
 
 ### !!! char And int Are Interchangeable
 
-```
+```java
 void method(int a, char b)
 method('c', 44)
 // method('g', 78900)