Chapter 7 – Arrays & the ArrayList

7.1 Introduction to Arrays

• Definition: An array is a collection of elements of the same data type, stored in contiguous memory locations.

• Purpose: Used to store multiple values efficiently.

Syntax

int[] arrayName = new int[size];

Example

int[] numbers = new int[5];

• Declaration and Initialization

int[] numbers = {1, 2, 3, 4, 5};

7.2 Accessing Array Elements

• Indexing: Use zero-based index to access elements.

System.out.println(numbers[0]); // Output: 1

• Modify Elements

numbers[2] = 10; // Updates the third element to 10

• Array Length

System.out.println(numbers.length); // Output: 5

7.3 Types of Arrays

1D Arrays

• Stores data in a linear format.

• Example

• double[] prices = new double[3];

• prices[0] = 10.5;

• prices[1] = 20.0;

prices[2] = 30.5;

2D Arrays

• Stores data in rows and columns (matrix).

• Syntax

int[][] matrix = new int[rows][cols];

• Example

• int[][] matrix = {

• {1, 2, 3},

• {4, 5, 6},

• {7, 8, 9}

• };

System.out.println(matrix[1][2]); // Output: 6

Jagged Arrays

• Arrays with rows of varying lengths.

• Example

• int[][] jaggedArray = new int[3][];

• jaggedArray[0] = new int[2];

• jaggedArray[1] = new int[3];

jaggedArray[2] = new int[1];

7.4 Looping Through Arrays

Using For Loop

for (int i = 0; i < numbers.length; i++) {

    System.out.println(numbers[i]);

}

Using Enhanced For Loop

for (int num : numbers) {

    System.out.println(num);

}

7.5 Common Array Operations

1. Finding Maximum/Minimum

2. int max = numbers[0];

3. for (int num : numbers) {

4. if (num > max) {

5. max = num;

6. }

}

1. Summing Elements

8. int sum = 0;

9. for (int num : numbers) {

10. sum += num;

}

1. Reversing an Array

• for (int i = 0, j = numbers.length – 1; i < j; i++, j–) {

13. int temp = numbers[i];

14. numbers[i] = numbers[j];

15. numbers[j] = temp;

}

7.6 Multidimensional Arrays

• Initialization

int[][] matrix = new int[3][3];

• Nested Loops for Traversal

• for (int i = 0; i < matrix.length; i++) {

• for (int j = 0; j < matrix[i].length; j++) {

• out.println(matrix[i][j]);

• }

}

7.7 Array Methods in Java

1. Sorting an Array

Arrays.sort(numbers);

1. Copying Arrays

int[] copy = Arrays.copyOf(numbers, numbers.length);

1. Comparing Arrays

boolean isEqual = Arrays.equals(arr1, arr2);

1. Filling Arrays

Arrays.fill(numbers, 5); // Fills array with 5

7.8 Limitations of Arrays

1. Fixed Size: Cannot dynamically resize after creation.

2. Homogeneous: Can store only one type of data.

3. No Built-in Methods for Complex Operations: Use libraries like ArrayList for dynamic arrays.

7.9 Best Practices for Using Arrays

1. Always validate array indices to avoid ArrayIndexOutOfBoundsException.

2. Use enhanced for-loops for readability when modification isn’t required.

3. Prefer using Java’s Arrays class for common operations.

Summary

• Arrays provide an efficient way to store and access multiple values of the same type.

• Mastering array operations is essential for solving problems involving data manipulation.

• Use multidimensional arrays for matrix-like structures and jagged arrays for irregular data layouts.