BeanShell用户手册：简单JavaScripting in Java

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"BeanShell用户手册是一份详细指南，涵盖了BeanShell 2.0b4版本的使用，它是一个小型、轻量级的Java脚本环境，支持简单的JavaScript语法，并且能够与Java语言无缝集成。这份手册包含了从快速入门到高级特性的全方位介绍，如下载与运行BeanShell、使用Java语句和表达式、实现接口、调用BeanShell从应用程序内部等。手册还详细解释了BeanShell的基本语法，包括标准Java语法、松散类型的Java语法、异常处理、变量的作用域以及自动装箱和拆箱等。此外，还介绍了如何导入类和包、创建文档友好的实体、编写脚本方法以及如何在脚本中实现接口。" BeanShell是一个基于Java的脚本语言，它的设计目标是提供一个轻量级的环境，让用户能够在类似JavaScript的语法下执行Java代码。BeanShell的用户手册首先介绍了Scripting vs. Application Languages的概念，探讨了脚本语言与应用语言的区别，以及BeanShell是如何打破这两者之间的屏障。接着，手册简述了BeanShell的历史和发展。快速入门部分，手册详细说明了如何下载和运行BeanShell，以及如何启动BeanShell的图形用户界面（GUI）。对于熟悉Java的开发者来说，可以很快上手，因为BeanShell支持标准的Java语句和表达式。同时，手册还列举了一些有用的BeanShell命令，帮助用户更高效地进行脚本编写。在基本语法部分，BeanShell允许使用标准的Java语法，但也有自己的松散类型系统，使得变量的声明更加灵活。异常处理机制与Java类似，但变量的作用域有其特殊性，包括变量修饰符、自动装箱和拆箱等特性。BeanShell支持导入Java的类和包，以及创建文档友好的实体，使得脚本更具可读性。 BeanShell的脚本方法和脚本对象章节，讲解了如何在脚本中定义和调用方法，以及如何通过实现接口来扩展BeanShell的功能。手册特别提到了使用'super'关键字来访问父类的方法，以及'this'引用在不同上下文中的用法。同时，还介绍了如何通过'scripted objects'和匿名内部类风格来实现接口。最后，手册还涵盖了同步方法的重访，讲解了在脚本中如何使用'synchronized'关键字，以及'this', 'super'和'global'的作用域修饰符的使用细节。总而言之，BeanShell用户手册是一份全面的指南，适合任何想要利用Java语法进行脚本编程的开发者。通过学习和实践手册中的内容，用户能够充分利用BeanShell的强大功能，将脚本与Java应用程序深度集成，实现更灵活和高效的编程。

BeanShell User's Manual

http://www.beanshell.org/manual/bshmanual.html[2013/3/25 16:03:56]

Convenience Syntax

In BeanShell you may access JavaBean properties as if they were fields:

button = new java.awt.Button();

button.label = "my button"; // Equivalent to: b.setLabel("my button");

print( button.label ); // Equivalent to print( b.getLabel() );

JavaBean properties are simply pairs of "setter" and "getter" methods that adhere to a naming convention. In the

above example BeanShell located a "setter" method with the name "setLabel()" and used it to assign the string

value. It then found the method named getLabel() to retrieve the value.

Boolean properties may optionally use the syntax "is" for their "getter". e.g.

Float f = new Float(42f);

print( f.infinite ); // Equivalent to print( f.isInfinite() ); // false

If there is any ambiguity with an actual Java field name of the object (e.g. label in the above example) then the

actual field name takes precedence. If you wish to avoid any ambiguity BeanShell provides an additional, uniform

syntax for accessing both Java Bean properties and Hashtable or Map entries. You may use the "{}" curly brace

construct with a String identifier as a qualifier on any variable of the appropriate type:

b = new java.awt.Button();

b{"label"} = "my button"; // Equivalent to: b.setLabel("my button");

h = new Hashtable();

h{"foo"} = "bar"; // Equivalent to: h.put("foo", "bar");

Where the java.util.Collections API is available, Maps are also supported.

Enhanced 'for' Loop

BeanShell supports the Java 1.5 style enhanced for-loop for iterating over collections and array types. (Note that

you do not have to be running Java 1.5 to use this feature).

List foo = getSomeList();

for ( untypedElement : foo )

print( untypedElement );

for ( Object typedElement: foo )

print( typedElement );

int [] array = new int [] { 1, 2, 3 };

for( i : array )

print(i);

for( char c : "a string" )

print( c );

Supported iterable types include all the obvious things.

JDK 1.1+ - (no collections): Enumeration, arrays, Vector, String, StringBuffer

JDK 1.2+ - (w/collections): Collections, Iterator

See also the BshIterator API which supports the ehanced for-loop and allows iteration over these types using the

dynamically loaded BeanShell Collection manager.

Switch Statements

In BeanShell, the switch statement may be used not only with numeric types but with objects. For example, you

BeanShell User's Manual

http://www.beanshell.org/manual/bshmanual.html[2013/3/25 16:03:56]

may switch on Dates and Strings which are compared for equality with their equals() methods:

dateobj = new Date();

switch( dateobj )

{

case newYears:

break;

case christmas:

break;

default:

}

Auto Boxing and Unboxing

"Boxing" and "Unboxing" are the terms used to describe automatically wrapping a primitive type in a wrapper

class and unwrapping it as necessary. Boxing is a feature of Java (SDK1.5) and has been supported in BeanShell

for many years.

BeanShell supports boxing and unboxing of primitive types. For example:

int i=5;

Integer iw = new Integer(5);

print( i * iw ); // 25

Vector v = new Vector();

v.put(1);

int x = v.getFirstElement();

Importing Classes and Packages

In BeanShell as in Java, you can either refer to classes by their fully qualified names, or you can import one or

more classes from a Java package.

// Standard Java

import javax.xml.parsers.*;

import mypackage.MyClass;

In BeanShell import statements may appear anywhere, even inside a method, not just at the top of a file. In the

event of a conflict, later imports take precedence over earlier ones.

A somewhat experimental feature is the "super import". With it you may automatically import the entire classpath,

like so:

import *;

The first time you do this BeanShell will map out your entire classpath; so this is primarily intended for interactive

use. Note that importing every class in your classpath can be time consuming. It can also result in a lot of

ambiguities. Currently BeanShell will report an error when resolving an an ambiguous import from mapping the

entire classpath. You may disambiguate it by importing the class you intend.

Tip:

The BeanShell which() command will use the classpath mapping capability to tell you where exactly in your

classpath a specified class is located:

bsh % which( java.lang.String );

Jar: file:/usr/java/j2sdk1.4.0/jre/lib/rt.jar

See "Class Path Management" for information about modifying the BeanShell classpath at run-time with the

addClassPath() or setClassPath() commands.

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