JAVA ARRAY NOTES_day-1

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🔷 JAVA ARRAY NOTES 🔷

1) WHY ARRAY?

Before Array:
int a = 10;
int b = 20;
int c = 30;

Problem:

• Too many variables
• No sequential memory
• Difficult to manage
• Hard to use loops

Solution → ARRAY

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2) WHAT IS AAN RRAY?

An array is a data structure that stores
multiple values of the same data type
in contiguous (sequential) memory location.

Syntax:

datatype[] arrayName;

Example:
int[] arr;

Memory Allocation:
arr = new int[5];

OR

int[] arr = new int[5];

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3) MEMORY REPRESENTATION

int[] arr = {10,20,30,40};

Index Value

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0 10
1 20
2 30
3 40

✔ Index starts from 0
✔ Last index = length - 1
✔ Stored in Heap memory
✔ Continuous memory allocation

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4) CHARACTERISTICS OF ARRAY

1. Homogeneous
   -> Same data type only.

2. Fixed Size
   -> Size cannot be changed after creation.

3. Indexed-Based
   -> arr[0], arr[1], arr[2] ...

4. Contiguous Memory
   -> Elements stored next to each other.

5. Default Values
   int -> 0
   double -> 0.0
   boolean -> false
   object -> null

6. Fast Access
   -> O(1) time complexity.

7. Length Property
   -> arr. length (variable, not method)

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5) TYPES OF ARRAYS

1)Single-Dimensionall Array
2) Multi-Dimensional Array

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6) WAYS TO CREATE AN ARRAY

Method 1:
int[] arr = new int[5];

Method 2:
int[] arr = {10,20,30,40};

Method 3 (Anonymous Array):
int[] arr = new int[]{100,200,300};

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7) PROGRAMS

1) SUM OF ARRAY

public class SumArray {
public static void main(String[] args) {

    int[] arr = {10,20,30,40};
    int sum = 0;

    for(int num : arr){
        sum = sum + num;
    }

    System.out.println("Sum = " + sum);
}

}

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2) REVERSE ARRAY

public class ReverseArray {
public static void main(String[] args) {

    int[] arr = {10,20,30,40};

    for(int i = arr.length - 1; i >= 0; i--){
        System.out.print(arr[i] + " ");
    }
}

}

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3) MINIMUM ELEMENT

public class MinArray {
public static void main(String[] args) {

    int[] arr = {12,5,78,3,9};
    int min = arr[0];

    for(int num : arr){
        if(num < min){
            min = num;
        }
    }

    System.out.println("Minimum = " + min);
}

}

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8) DRAWBACKS OF ARRAY

1) Fixed Size
2) Insertion is costly
3) Deletion is costly
4) No built-in methods
5) Only the same type of elements

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9) IMPORTANT EXAM POINTS

✔ Array is an object in Java.
✔ Stored in Heap memory.
✔ Size is fixed.
✔ Index starts from 0.
✔ Access time is O(1).
✔ Out of range → ArrayIndexOutOfBoundsException.

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🔥 FINAL SUMMARY 🔥

ARRAY =

• Same type elements
• Continuous memory
• Fixed size
• Index-based
• Fast access

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If you want next:
1) 2D Array Notes (console style)
2) 20 Array Practice Programs
3) Array Interview Questions
4) Internal Working Diagram Explanation