Chapter 9: Working with Arrays and Strings 📊

This cheat sheet covers arrays and string handling for Chapter 9 of the GSEB Std 12 Computer Studies syllabus.

🎯 Key Concepts

• Array: A fixed-size collection of data of the same type stored in continuous memory.
• String: An immutable object representing a sequence of characters.
• Index: Position of an element (starts from 0).

---

🛠️ Java Arrays (1D & 2D)

1. 1D Array Syntax

• Declaration: int[] marks;
• Creation: marks = new int[5]; (Values initialized to 0 by default).
• Access: marks[0] = 95;

2. 2D Array Syntax (Matrix)

• Declaration: int[][] matrix = new int[2][3]; (2 rows, 3 columns).
• Access: matrix[row][col].

3. The java.util.Arrays Helper Class

Method	Description
Arrays.sort(arr)	Sorts the array in ascending order.
Arrays.fill(arr, val)	Fills the whole array with a single value.
Arrays.equals(arr1, arr2)	Returns true if two arrays have same elements in same order.
Arrays.binarySearch(arr, key)	Finds the index of an element (array must be sorted).

---

📜 Java Strings (Immutable)

1. Key Properties

• Immutability: Once a String is created, its value cannot be changed.
• String Pool: Efficient memory storage for literals.

2. Essential String Methods

Method	Type	Description
length()	Method	Returns the number of characters.
charAt(i)	Method	Returns character at index i.
substring(start, end)	Method	Returns part of string from start to end-1.
equals(other)	Method	Case-sensitive equality check.
equalsIgnoreCase(other)	Method	Case-insensitive equality check.
replace('o', 'a')	Method	Replaces all 'o' with 'a'.

---

💡 Board Focus: High-Weightage Points 👔

• MCQ Alert: length is a property for arrays (arr.length); length() is a method for strings (s.length()).
• MCQ Alert: Index of the last element is always length - 1.
• MCQ Alert: Array size cannot be changed after creation.
• MCQ Alert: Calendar and Date classes are in the java.util package.
• MCQ Alert: System.arraycopy() is used to copy arrays.

---

Board Exam Secret

GSEB often asks about the "Default Values" of arrays. Remember: int = 0, boolean = false, float/double = 0.0, and objects = null.

---

Std 12 Hub | [End of Series]