Arrays

Array Basics

Arrays are a special type of object that consists of a numbered sequence of memory boxes.

Arrays consist of:

• A fixed integer length, N
• A sequence of N memory boxes (N = length) where all boxes are of the same type, and are numbered 0 through N - 1.

Array Creation

Three notations for array creation are just the same.

• int[] x = new int[3];
• int[] y = new int[]{1, 2, 3, 4, 5};
• int[] z = {9, 10, 11, 12, 13};

Array Access and Modification

int[] z = null; // Null pointer
int[] x, y; // Uninitialized pointer

x = new int[]{1, 2, 3, 4, 5};
y = x; // Point to the same address
x = new int[]{-1, 2, 5, 4, 99};
y = new int[3];
z = new int[0]; // Empty array
int xL = x.length;

String[] s = new String[6];
s[4] = "ketchup";
s[x[3] - x[1]] = "muffins";

Java arrays only perform bounds checking at runtime.

Array Copying

System.arraycopy(src, src_beg, dst, dst_beg, len);

System.arraycopy takes five parameters:

• The array to use as a source
• Where to start in the source array
• The array to use as a destination
• Where to start in the destination array
• How many items to copy

2D Arrays

A 2D array in Java is actually just an array of arrays.

Consider the code int[][] bamboozle = new int[4][]. This creates an array of integer arrays called bamboozle. Specifically, this creates exactly four memory boxes, each of which can point to an array of integers (of unspecified length).