Introduction to arrays

Introduction to Java

Jim White

Java Developer

Array is ...

An array is a collection of values stored as a single variable

Array is ... a row of lockers!

An array represented as a row of lockers, where each locker has a numbered label, or index

Declaring and filling arrays

Using square brackets []

// Declare array variable
int[] prices;

// Assign value
prices = {10, 20, 30, 40};

Values of 10, 20, 30, and 40 in the first, second, third, and fourth locker respectively

Accessing elements

Using []:

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

// Accessing first element
int firstElement = prices[0]; // Value is 10

// Accessing second element
int secondElement = prices[1]; // Value is 20

Java starts indexing from 0

Changing value of an element

Change value by assigning new value to specific index

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


// Change value of third element to 95
prices[2] = 95;

Array length is fixed

Array's length is fixed on creation

int[] itemIDs = {10, 20, 30, 40, 50};

// Accessing sixth element that isn't there 
itemIDs[5] = 60; // <- This will cause an error

Check array's length using .length property

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

int pricesLength = prices.length; // Value is 4

.length doesn't use any brackets for arrays

Printing out values

We can print out individual values:

class ArrayElementPrinting {
  public static void main (String[] args){
    int[] prices = {10, 20, 30, 40};

    // Printing element by element
    System.out.println(prices[0]);
    System.out.println(prices[1]);
  }
}

10
20

Trying to print an entire array

Printing whole array returns representation:

class ArrayPrinting {
  public static void main (String[] args){
    int[] prices = {10, 20, 30, 40};

    // Printing whole thing
    System.out.println(prices);
  }
}

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Arrays of other things

// Array of Strings
String[] productNames = {"Organic Honey", 
                         "Cold Brew Coffee", 
                         "Dark Chocolate Bar"};

Values in an array

Not limited to just numbers or Strings

All values in an array must have the same type

Recap

Arrays are useful of storing multiple values of the same type
Arrays are indexed from 0
Arrays have fixed length

// Declare and assign
int[] prices = {10, 20, 30, 40};

// Retrieve
int secondElement = prices[1];

// Update
prices[1] = 25;

// Length
// Value is 4
int pricesLength = prices.length;

Let's practice!

Introduction to Java