ArrayLists and Collection Framework

Fixed-Size Arrays

• Arrays have a fixed length that cannot be changed after creation.
• Memory is allocated during creation, before elements are added.
• Adding extra elements after creation is not possible.
• Resizing requires creating a new array and copying elements.

ArrayList Class

• ArrayList is a built-in class in Java Collections Framework.
• Supports dynamic arrays that can increase/decrease in size.
• Elements can be inserted/deleted at specific positions.
• ArrayList has many methods to manipulate stored objects.
• Without Generics, ArrayList can hold any type of object.

Collection Framework

• A framework offers a ready-made architecture with classes and interfaces.
• A collection represents a group of objects.
• All classes/interfaces are in the java.utli package.

How to use ArrayList

• Step 01: Import ArrayList class
• Step 02: Create/Declare an object from ArrayList class
• Step 03: Add elements (objects) to the created arraylist object
• Step 04: Modifying Elements
• Step 05: Accessing Elements
• Step 06: Removing Elements
• Step 07: Retrieve Size & Emptiness
• Step 08: Iteration - Classic For Loop
• Step 09: Iteration - Enhanced For Loop

Generics

• Generics mean parameterized types.
• Allows types (Integer, String, etc.) to be parameters for methods, classes, & interfaces.
• Before Generics, Java used Object to store any type of data (lacked type safety).
• Generics add type safety by restricting the types of values an ArrayList can hold.

Limitations of Generics

• Generics work only with Reference Types, not primitive data types (int, char).
• Compile-time errors occur when using primitive types directly.
• Use wrapper classes to encapsulate primitive types.

Wrapper Classes

• Wrapper classes convert primitive datatypes into objects and vice versa.
• Each primitive datatype has a corresponding wrapper class in the java.lang package.