Collections - Scripting in Java: Integrating with Groovy and JavaScript - page 237

Typed Arrays
Typed arrays in Nashorn are array-like objects. They provide views of raw binary data
called the buffer . You can have multiple typed views of the same buffer. Suppose you have
a buffer of 4 bytes. You can have an 8-bit signed integer typed array view of the buffer that
will represent four 8-bit signed integers. At the same time, you can have a 32-bit unsigned
integer typed array view of the same buffer that can represent one 32-bit unsigned integer.

■ a typed array is an array-like object providing a typed view of raw binary data in
memory. the specification for typed arrays implementation in nashorn can be found at
https://www.khronos.org/registry/typedarray/specs/latest/ .

Tip

The buffer in a typed array is represented by an ArrayBuffer object. Using an
ArrayBuffer object directly or indirectly, you can create a typed array view. Once you
have a typed array view, you can write or read data of the specific type supported by the
typed array view, using the array-like syntax. In the next section, I will discuss how to
work with ArrayBuffer objects. In the subsequent sections, I will discuss different types
of typed array views (or simply called typed arrays).

The ArrayBuffer Object
An ArrayBuffer object represents a fixed-length buffer of raw binary data. The contents
of an ArrayBuffer does not have a type. You cannot directly modify the data in an
ArrayBuffer ; you must create and use one of the typed views on it to do so. It contains
few properties and methods to copy its contents into another ArrayBuffer and to query
its size.
The ArrayBuffer constructor takes one argument that is the length of the buffer in
bytes. The length of an ArrayBuffer object cannot be changed, after it is created. The
object has a read-only property named byteLength that represents the length of the
buffer. The following statement creates a buffer of 32 bytes and prints its length:

// Create a ArrayBuffer of 32 bytes
var buffer = new ArrayBuffer(32);

// Assigns 32 to len
var len = buffer.byteLength;

■ When you create an ArrayBuffer , its contents are initialized to zero. there is no
way to initialize its contents with values other than zero, at the time of creation. each byte in
the ArrayBuffer uses a zero-based index. the first byte has indexed 0, second 1, third 2,
and so on.

Tip