Arrays: every key term you need

Arrays: Basics

Fixed-size collection of same type. Declaration: int[] arr = new int[5];. Index 0 to length-1.

Array Indexing

Access element: arr[i]. Range 0 to length-1. ArrayIndexOutOfBoundsException if invalid index.

Array Initialization

int[] arr = {1, 2, 3, 4, 5}; or int[] arr = new int[5]; (defaults to 0). Size set at creation.

Array Length

arr.length gives size (not method, property). Used in loops: for (int i=0; i<arr.length; i++).

Arrays as Parameters

Method receives array reference; modifications affect original array. Pass by reference (objects), not value.

Array Algorithms: Search

Linear search: loop through checking each element. Fastest when small. Binary search: requires sorted array; O(log n).

Array Algorithms: Sort

Arrays.sort(arr) built-in. Custom sort needs comparison logic (Comparable interface).

2D Arrays

int[][] matrix = new int[rows][cols];. Jagged arrays: each row different length. Access: matrix[i][j].

2D Array Traversal

Nested loops: for each row, for each column. Standard: row-major (right-to-left, top-to-bottom).

Arrays vs ArrayList

Array: fixed size, primitives allowed, faster. ArrayList: dynamic, objects only, slower. ArrayList wraps primitives (Integer, Double).

Unit 6 Summary

Arrays fixed-size collections; indexed 0 to length-1. 2D arrays for tables/matrices. Algorithms: search, sort. ArrayList more flexible.

More AP Computer Science A guides

• Primitives
• Using Objects
• Boolean Expressions
• Loops
• Writing Classes