Java Programming · Week 7
Step 1 of 4
Welcome to our Java Arrays Tutorial! This lesson covers the basics of arrays in Java, including how to create, initialize, and manipulate arrays. Arrays are fundamental data structures that allow you to store multiple values of the same type.
By the end of this lesson, you'll be able to create arrays, use common array methods, and traverse arrays using loops.
An array is a collection of variables that are stored in a contiguous block of memory and can be accessed using an index. Arrays are used to store multiple values of the same type in a single variable.
Think of an array as a row of lockers in a hallway. Each locker is numbered (indexed), and you can store one item (a value) in each locker.
Syntax:
// Declaring an array of integers
int[] numbers = new int[5];
// Initializing an array
int[] numbers = {1, 2, 3, 4, 5};Accessing Array Elements:
Array elements are accessed using their index, which starts at 0. For example, numbers[0] gives the first element, and numbers[4] gives the last element in the example above.
int firstNumber = numbers[0]; // Accessing the first element
int lastNumber = numbers[4]; // Accessing the last elementCreate an array of 5 double values that represent the grades of a student. Assign values to each element in the array and print the first and last grades.
public class StudentGrades {
public static void main(String[] args) {
// Create an array of 5 double values representing grades
// Assign values to each element
// Print the first and last grades
}
}
Java provides an Arrays class in the java.util package, which contains various methods for manipulating arrays, such as sorting, searching, and comparing arrays.
Commonly Used Array Methods:
Arrays.sort(array): Sorts the array in ascending order.Arrays.toString(array): Converts the array to a String for easy printing.Arrays.fill(array, value): Fills the array with the specified value.Arrays.equals(array1, array2): Checks if two arrays are equal.Arrays.binarySearch(array, key): Searches for a specific value within a sorted array. Returns the index of the key if found, otherwise returns a negative value.Arrays.copyOf(array, newLength): Copies the original array into a new array with the specified length.array.length: Returns the length (number of elements) of the array.Example:
import java.util.Arrays;
public class ArrayMethodsExample {
public static void main(String[] args) {
int[] numbers = {5, 3, 8, 1, 2};
// Sorting the array
Arrays.sort(numbers);
System.out.println("Sorted array: " + Arrays.toString(numbers));
// Filling the array with a single value
Arrays.fill(numbers, 7);
System.out.println("Array after fill: " + Arrays.toString(numbers));
// Searching for a value in the sorted array
int index = Arrays.binarySearch(numbers, 7);
System.out.println("Index of 7 in the array: " + index);
// Copying the array
int[] newArray = Arrays.copyOf(numbers, 10);
System.out.println("New array after copy: " + Arrays.toString(newArray));
// Checking if two arrays are equal
int[] otherArray = {7, 7, 7, 7, 7};
boolean isEqual = Arrays.equals(numbers, otherArray);
System.out.println("Are the two arrays equal? " + isEqual);
// Getting the length of the array
System.out.println("Length of the array: " + numbers.length);
}
}Create an array of 6 integers. Use the Arrays.fill() method to initialize all elements with the value 10. Then, sort the array, perform a binary search for the number 10, and print the index. Check the length of the array using the length property and print it. Finally, compare this array to another array with identical elements and print the result.
import java.util.Arrays;
public class ArrayMethodsPractice {
public static void main(String[] args) {
// Create an array of 6 integers
// Use Arrays.fill() to initialize all elements with 10
// Sort the array
// Perform binary search for 10 and print the index
// Print the length of the array
// Compare this array to another identical array and print the result
}
}
Array traversing refers to accessing each element of an array in sequence. This is often done using loops like for or while.
Traversing with a For Loop:
public class ArrayTraversal {
public static void main(String[] args) {
int[] numbers = {10, 20, 30, 40, 50};
// Using a for loop to traverse the array
for (int i = 0; i < numbers.length; i++) {
System.out.println("Element at index " + i + ": " + numbers[i]);
}
}
}Traversing with an Enhanced For Loop:
public class ArrayTraversal {
public static void main(String[] args) {
int[] numbers = {10, 20, 30, 40, 50};
// Using an enhanced for loop to traverse the array
for (int num : numbers) {
System.out.println("Number: " + num);
}
}
}Create an array of 10 integers. Use a loop to fill the array with even numbers. Then, traverse the array and print each element.
public class EvenNumbersArray {
public static void main(String[] args) {
// Create an array of 10 integers
// Use a loop to fill the array with even numbers (2, 4, 6, ...)
// Traverse the array and print each element
}
}