Collection Framework

What is Framework?

• A framework is a pre-written set of classes, libraries, and rules that help developers build applications faster.

Why Collection Framework?

• Java arrays are used to store multiple values of the same data type in a single variable. However, arrays have several limitations, which is why the Java Collection Framework was introduced.

Disadvantages of Array :

Fixed Size (Static Memory Allocation) :

• The size of an array must be defined when it is created, and it cannot be changed later.

Arrays Store Only Similar Data Types(Homowgeneous) :

• An array can store only one type of data.

No Built-in Methods :

• Arrays do not provide built-in functions for common operations.

For example:
Sorting
Searching
Adding elements
Removing elements
You must write extra code manually.

Memory Wastage

• If you declare a large array but use only a few elements, unused memory is wasted.

Advantages of Collection :

Dynamic Size (Resizable):

• Collections can grow or shrink automatically as elements are added or removed.

Built-in Methods:

• Collections provide many built-in methods that simplify programming.

Reduces Programming Effort :

• Because collections provide ready-made functionality. Less code,Faster development, and Easier maintenance.

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ArrayList :

• ArrayList is one of the most commonly used classes in the Java Collections Framework.
• arraylist is a class that implements interface List.
• It is a class in java.util package.
• Default initial capacity of ArrayList is 10.

Features:

• Maintains insertion order.
• Allows duplicates.
• Dynamic size (can grow automatically).
• Can store null values.

Methods of ArrayList :

add() – Add elements :

ArrayList al = new ArrayList();
//Adds an element to the list

al.add("Pen");
al.add(10);
al.add("Pencil");
al.add(1);
System.out.println(al);

Output :
[Pen, 10, Pencil, 1]

//Add element at specific index

al.add(0,"NoteBook");
System.out.println(al);

Output :
[NoteBook, Pen, 10, Pencil, 1]

set() – Access element :

• Replace element at a specific index.

al.set(2,"Book");
System.out.println(al);
Output :
[NoteBook, Pen, Book, Pencil, 1]

get() – Access element :

Retrieve element using index.

System.out.println(al.get(0));
Output : NoteBook

remove() – Delete element :

• Remove by index :

al.remove(2);
System.out.println(al);

Output: 
[NoteBook, Pen, Pencil, 1]

• Remove by object :

al.remove("Pen");
System.out.println(al);

Output:
[NoteBook, Pencil, 1]

size() – Get number of elements:

System.out.println(al.size());
Output : 3

contains() – Check element existence:

System.out.println(al.contains(1));
Output : true

indexOf() – Find element index :

System.out.println(al.indexOf("Pencil"));
output: true

clear() – Remove all elements :

isEmpty() – Check if list is empty:

al.clear();
System.out.println(al.isEmpty());
System.out.println(al);

output: []

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What is HashSet?

• Hashet is a class that implements the set interface.
• It doesn't allow duplicate values.
• Objects are not sorted in insertion order.
• Only one null value is allowed.

Example :
        HashSet hst = new HashSet();
        hst.add("abi");
        hst.add("baby");
        hst.add("cat");
        hst.add("cat");
        hst.add(null);
        hst.add(null);
        System.out.println(hst);

Output:

[null, cat, baby, abi]

HashSet vs ArrayList: