Javascript [Electronic resources] : The Definitive Guide (4th Edition) نسخه متنی

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Synopsis

javaarray.length // The length of the array
javaarray[index] // Read or write an array element

Properties

length

A read-only integer that specifies the number of elements in the Java
array represented by the JavaArray object.

Description

The JavaArray object is a JavaScript representation of a Java array
that allows JavaScript code to read and write the elements of the
array using familiar JavaScript array syntax. In addition, the
JavaArray object has a length field that specifies
the number of elements in the Java array.

When reading and writing values from array elements, data conversion
between JavaScript and Java representations is automatically handled
by the system. See Chapter 22 for full details.

Usage

Note that Java arrays differ from JavaScript arrays in a couple of
important aspects. First, Java arrays have a fixed length that is
specified when they are created. For this reason, the JavaArray
length field is read-only. The second difference
is that Java arrays are

typed (i.e., their
elements must all be of the same type of data). Attempting to set an
array element to a value of the wrong type results in a JavaScript
error or exception.

Example

java.awt.Polygon is a JavaClass object. We can
create a JavaObject representing an instance of the class like this:

p = new java.awt.Polygon(  ); 

The object p has properties
xpoints and ypoints, which are
JavaArray objects representing Java arrays of integers. We can
initialize the contents of these arrays with JavaScript code like the
following:

for(int i = 0; i < p.xpoints.length; i++)
p.xpoints[i] = Math.round(Math.random(  )*100);
for(int i = 0; i < p.ypoints.length; i++)
p.ypoints[i] = Math.round(Math.random(  )*100); 

See Also

getClass( ), JavaClass, JavaObject, JavaPackage, the
java property of the Window object; Chapter 22