Before you jump into advanced Data Structures like stacks, queues, or hash tables, there’s one concept you must fully understand Arrays.
If arrays are unclear, everything else in DSA will feel complicated.
Let’s fix that in the simplest way possible.
What is an Array?
Think of an array like a row of lockers.
Each locker:
- Has a fixed position (index)
- Stores one value
- Can be accessed instantly if you know the index
In Java, an array stores elements:
- Of the same type
- In continuous memory locations
Why Arrays Are Fast (O(1) Access)
Arrays allow direct access using index.
Example:
int[] arr = {2, 3, 5, 7};
System.out.println(arr[2]); // 5
- No searching required
- Direct memory access
- That’s why time complexity is O(1)
Key Properties of Arrays
- Fixed Size → cannot change after creation
- Contiguous Memory → stored in a continuous block
- Index-Based Access → starts from 0
- Homogeneous → same data type
Array Declaration in Java
// Declaration
int[] numbers;
// Allocation
numbers = new int[5];
// Initialization
int[] primes = {2, 3, 5, 7};
String[] names = new String[]{"Alice", "Bob"};
Accessing Elements
int first = primes[0]; // 2
primes[2] = 11; // update value
int length = primes.length;
Key Insights
- Arrays are objects in Java
- They come with a .length property
- Default values:
- int → 0
- boolean → false
- object → null
For More: https://www.quipoin.com/tutorial/data-structure-with-java/array-introduction
