Array
Lab Objective
The goal of this lab is to provide you with hands-on experience working with Java arrays and iterating over an Array using loops.
Instructions
Example 1: Access Array Elements
Create a class named arraydemoOne and write the below code.
public class arraydemoOne {
public static void main(String[] args) {
// create an array
int[] age = {12, 4, 5, 2, 5};
// access each array elements
System.out.println("Accessing Elements of an Array:");
System.out.println("First Element: " + age[0]);
System.out.println("Second Element: " + age[1]);
System.out.println("Third Element: " + age[2]);
System.out.println("Fourth Element: " + age[3]);
System.out.println("Fifth Element: " + age[4]);
}
}
Output:
Accessing Elements of an Array:
First Element: 12
Second Element: 4
Third Element: 5
Fourth Element: 2
Fifth Element: 5
In the above example, notice that we are using the index number to access each element of the array.
We can use loops to access all the array elements at once.
Example 2: Using for Loop
Create a class named arraydemoTwo and write the code below in it
public class arraydemoTwo {
public static void main(String[] args) {
// create an array
int[] age = {12, 4, 5};
// loop through the array
// using for loop
System.out.println("Using for Loop:");
for(int i = 0; i < age.length; i++) {
System.out.println(age[i]);
}
}
}
Output:
Using for Loop:
12
4
5
In the above example, we are using the for Loop in Java to iterate through each element of the array. Notice the expression inside the loop, age.length.
Example 3: Iterating Over an Array using EnhancedForLoop
Create a class named EnhancedForLoop and write the code below.
public class EnhancedForLoop {
public static void main(String[] args) {
String[] names = { "New York", "Dallas", "Las Vegas", "Florida" };
for (String name : names) {
System.out.println(name);
}
}
}
Output:
New York
Dallas
Las Vegas
Florida
Example 4: Compute the Sum and Average of Array Elements
Create a class named arraydemothree and write the code below.
public class arraydemothree {
public static void main(String[] args) {
int[] numbers = {2, -9, 0, 5, 12, -25, 22, 9, 8, 12};
int sum = 0;
Double average;
// access all elements using for each loop
// add each element in sum
for (int number: numbers) {
sum += number;
}
// get the total number of elements
int arrayLength = numbers.length;
// calculate the average
// convert the average from int to double
average = ((double)sum / (double)arrayLength);
System.out.println("Sum = " + sum);
System.out.println("Average = " + average);
}
}
Output:
Sum = 36
Average = 3.6
In the above example, we have created an array of named numbers. We have used them for...each loop to access each array element. Inside the loop, we calculate the sum of each element. Notice the line: int arrayLength = numbers.length; Here, we are using the length attribute of the array to calculate the size of the array. We then calculate the average using: average = ((double)sum / (double)arrayLength); As you can see, we are converting the int value into a double. This is called "type casting” in Java.
Example 5: Mean and Standard Deviation
Find the mean and standard deviation of the numbers kept in an array.
Create a class named MeanSDArray and write the code below.
public class MeanSDArray {
public static void main(String[] args) {
// Declare variable
int[] marks = {74, 43, 58, 60, 90, 64, 70};
int sum = 0;
int sumSq = 0;
double mean, stdDev;
// Compute sum and square-sum using loop
for (int i = 0; i < marks.length; ++i) {
sum += marks[i];
sumSq += marks[i] * marks[i];
}
mean = (double)sum / marks.length;
stdDev = Math.sqrt((double)sumSq / marks.length - mean * mean);
// Print results
System.out.printf("Mean is: %.2f%n", mean);
System.out.printf("Standard deviation is: %.2f%n", stdDev);
}
}
Output:
Mean is: 65.57
Standard deviation is: 13.56
Example 6: Insert an Element at the end of an Array in Java
Create a class named insertElements and write the code below.
import java.util.Scanner;
public class insertElements {
public static void main(String[] args) {
int i, element;
int[] arr = new int[11];
Scanner scan = new Scanner(System.in);
System.out.print("Enter 10 Elements: ");
for(i=0; i<10; i++)
arr[i] = scan.nextInt();
System.out.print("Enter an Element to Insert: ");
element = scan.nextInt();
arr[i] = element;
System.out.println("\\\\nNow the new array is: ");
for(i=0; i<11; i++)
System.out.print(arr[i]+ " ");
}
}
The snapshot given below shows the sample run of the above program, with user input 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 as ten elements and 500 as the new element to insert at the end of array:
Enter 10 Elements: 10
20
30
40
50
60
70
80
90
100
Enter an Element to Insert: 500
Now the new array is:
10 20 30 40 50 60 70 80 90 100 500Last updated