path: root/src/overview.html
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authorjlaskey <none@none>2012-12-21 16:36:24 -0400
committerjlaskey <none@none>2012-12-21 16:36:24 -0400
commitb5b4ea8613543cf553f0b7c0668872769057a081 (patch)
tree7383cfecccd985a21e16d2e5f9756f27c725bbe3 /src/overview.html
parent97e525f8f856419b8922a89308d6ab60f680e846 (diff)
8005403: Open-source Nashorn
Reviewed-by: attila, hannesw, lagergren, sundar Contributed-by: james.laskey@oracle.com, akhil.arora@oracle.com, andreas.woess@jku.at, attila.szegedi@oracle.com, hannes.wallnoefer@oracle.com, henry.jen@oracle.com, marcus.lagergren@oracle.com, pavel.semenov@oracle.com, pavel.stepanov@oracle.com, petr.hejl@oracle.com, petr.pisl@oracle.com, sundararajan.athijegannathan@oracle.com
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+ Copyright (c) 2010, 2012, Oracle and/or its affiliates. All rights reserved.
+ This code is free software; you can redistribute it and/or modify it
+ under the terms of the GNU General Public License version 2 only, as
+ published by the Free Software Foundation. Oracle designates this
+ particular file as subject to the "Classpath" exception as provided
+ by Oracle in the LICENSE file that accompanied this code.
+ This code is distributed in the hope that it will be useful, but WITHOUT
+ ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ version 2 for more details (a copy is included in the LICENSE file that
+ accompanied this code).
+ You should have received a copy of the GNU General Public License version
+ 2 along with this work; if not, write to the Free Software Foundation,
+ Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ or visit www.oracle.com if you need additional information or have any
+ questions.
+Nashorn is a runtime environment for programs written in ECMAScript 5.1.
+The recommended way to use Nashorn is through the <a href="http://jcp.org/en/jsr/detail?id=223" target="_top">JSR-223
+"Scripting for the Java Platform"</a> APIs found in the {@link javax.script} package. Usually, you'll obtain a
+{@link javax.script.ScriptEngine} instance for Nashorn using:
+import javax.script.*;
+ScriptEngine nashornEngine = new ScriptEngineManager().getEngineByName("nashorn");
+and then use it just as you would any other JSR-223 script engine. See
+<a href="jdk/nashorn/api/scripting/package-summary.html">{@code jdk.nashorn.api.scripting}</a> package
+for details.
+Nashorn is 100% compliant with the <a href="http://www.ecma-international.org/publications/standards/Ecma-262.htm"
+target="_top">ECMA-262 Standard, Edition 5.1</a>. It requires a Java Virtual Machine that implements the
+<a href="http://jcp.org/en/jsr/detail?id=292" target="_top">JSR-292 "Supporting Dynamically Typed Languages on the Java
+Platform"</a> specification (often referred to as "invokedynamic"), as well as the already mentioned JSR-223.
+<h1>Interoperability with the Java platform</h1>
+In addition to being a 100% ECMAScript 5.1 runtime, Nashorn provides features for interoperability of the ECMAScript
+programs with the Java platform. In general, any Java object put into the script engine's context will be visible from
+the script. In terms of the standard, such Java objects are not considered "native objects", but rather "host objects",
+as defined in section 4.3.8. This distinction allows certain semantical differences in handling them compared to native
+objects. For most purposes, Java objects behave just as native objects do: you can invoke their methods, get and set
+their properties. In most cases, though, you can't add arbitrary properties to them, nor can you remove existing
+<h2>Java collection handling</h2>
+Native Java arrays and {@link java.util.List}s support indexed access to their elements through the property accessors,
+and {@link java.util.Map}s support both property and element access through both dot and square-bracket property
+accessors, with the difference being that dot operator gives precedence to object properties (its fields and properties
+defined as {@code getXxx} and {@code setXxx} methods) while the square bracket operator gives precedence to map
+elements. Native Java arrays expose the {@code length} property.
+<h2>ECMAScript primitive types</h2>
+ECMAScript primitive types for number, string, and boolean are represented with {@link java.lang.Number},
+{@link java.lang.CharSequence}, and {@link java.lang.Boolean} objects. While the most often used number type is
+{@link java.lang.Double} and the most often used string type is {@link java.lang.String}, don't rely on it as various
+internal optimizations cause other subclasses of {@code Number} and internal implementations of {@code CharSequence} to
+be used.
+<h2>Type conversions</h2>
+When a method on a Java object is invoked, the arguments are converted to the formal parameter types of the Java method
+using all allowed ECMAScript conversions. This can be surprising, as in general, conversions from string to number will
+succeed according to Standard's section 9.3 "ToNumber" and so on; string to boolean, number to boolean, Object to
+number, Object to string all work. Note that if the Java method's declared parameter type is {@code java.lang.Object},
+Nashorn objects are passed without any conversion whatsoever; specifically if the JavaScript value being passed is of
+primitive string type, you can only rely on it being a {@code java.lang.CharSequence}, and if the value is a number, you
+can only rely on it being a {@code java.lang.Number}. If the Java method declared parameter type is more specific (e.g.
+{@code java.lang.String} or {@code java.lang.Double}), then Nashorn will of course ensure the required type is passed.
+<h2>SAM types</h2>
+As a special extension when invoking Java methods, ECMAScript function objects can be passed in place of an argument
+whose Java type is so-called "single abstract method" or "SAM" type. While this name usually covers single-method
+interfaces, Nashorn is a bit more versatile, and it recognizes a type as a SAM type if all its abstract methods are
+overloads of the same name, and it is either an interface, or it is an abstract class with
+a no-arg constructor. The type itself must be public, while the constructor and the methods can be either public or
+protected. If there are multiple abstract overloads of the same name, the single function will serve as the shared
+implementation for all of them, <em>and additionally it will also override any non-abstract methods of the same name</em>.
+This is done to be consistent with the fact that ECMAScript does not have the concept of overloaded methods.
+<h2>The {@code Java} object</h2>
+Nashorn exposes a non-standard global object named {@code Java} that is the primary API entry point into Java
+platform-specific functionality. You can use it to create instances of Java classes, convert from Java arrays to native
+arrays and back, and so on. The methods on the objects are directly implemented by public static methods on the class
+<a href="jdk/nashorn/internal/objects/NativeJava.html">{@code NativeJava}</a>, see that class for details on what
+functionality is available.
+<h2>Representations of Java types</h2>
+The method <a href="jdk/nashorn/internal/objects/NativeJava.html#type(java.lang.Object,%20java.lang.Object)">
+{@code Java.type(typeName)}</a> takes a name of a type, and returns an object representing a Java type. You can
+use that object to both create new instances of Java classes, as well as to access static fields and methods on them.
+The type object is distinct from the {@code java.lang.Class} object, which represents the reflective run-time type
+identity and doesn't carry i.e. static members. Again, see the link for {@code NativeJava} above for details.
+<h2>Other non-standard built-in objects</h2>
+In addition to {@code Java}, Nashorn also exposes some other non-standard built-in objects:
+<a href="jdk/nashorn/internal/objects/NativeJSAdapter.html">{@code JSAdapter}</a>,
+<a href="jdk/nashorn/internal/objects/NativeJavaImporter.html">{@code JavaImporter},
+<a href="jdk/nashorn/internal/runtime/NativeJavaPackage.html">{@code Packages}.</a>
+</body> \ No newline at end of file