Array Initialization in AP CSA

Arrays in Java are fixed-size, zero-indexed collections of a single type. Knowing how to declare, initialize, and access them correctly is the foundation of the entire Unit 4 exam weight.

Three Ways to Initialize an Array

// 1. Declare with size -- fills with default values
int[] scores = new int[5];     // [0, 0, 0, 0, 0]
double[] vals = new double[3]; // [0.0, 0.0, 0.0]
String[] names = new String[4];// [null, null, null, null]

// 2. Initializer list -- size inferred
int[] primes = {2, 3, 5, 7, 11};

// 3. Declare then assign
int[] data;
data = new int[10];

Default Values

Accessing Elements

int[] arr = {10, 20, 30, 40, 50};
System.out.println(arr[0]);             // 10 -- first element
System.out.println(arr[arr.length-1]);  // 50 -- last element
System.out.println(arr.length);         // 5 -- number of elements