1.11 Arrays

Learning Objectives

•Declare, allocate, and initialize one-dimensional arrays.
•Access and modify elements by index, and iterate with for/for-each.
•Explain why array size is fixed once created.

Introduction

An array is a fixed-size, ordered collection of elements of the same type, indexed from 0. Arrays are reference types in Java — declaring one creates a reference; the actual storage is allocated separately, either with `new` or an array literal.

Key Concepts

Declaration: `int[] scores;` — the brackets can also follow the variable name (`int scores[]`), but `type[] name` is the conventional style.

Allocation: `new int[5]` creates an array of five ints, each defaulting to 0.

Array literal shorthand: `int[] scores = {90, 85, 77};`.

`array.length` (no parentheses — it's a field, not a method) gives the element count.

Enhanced for-each loop: `for (int s : scores) { ... }` reads every element without manual indexing.

Java Syntax

Code Examples

The indexed loop prints each score with its position. The for-each loop sums every element without needing an index variable.

Common Mistakes

⚠Accessing an index outside `0` to `length - 1`, which throws `ArrayIndexOutOfBoundsException` at runtime.
⚠Confusing `.length` (a field on arrays) with `.length()` (a method on String).
⚠Assuming an array can grow — arrays are fixed-size; a new array must be created (or a resizable structure like `ArrayList` used instead) to hold more elements.

Practice

Practice 1

Programming Exercisemedium

Write a program that finds and prints the largest value in an int array of your choosing.

Summary

Arrays hold a fixed number of same-typed elements, indexed from 0, accessed via `.length` and either indexed or for-each loops. Out-of-bounds access is a common runtime error to guard against.

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