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Tip of the Day
Language: Java
Expertise: Advanced
Mar 6, 2003

The Beans Class


The standard Java library contains a host of valuable methods. Many of these are hidden away, such as Beans.isInstanceOf.

This method belongs to the java.beans.Beans class. However, it's an object version of the instanceof keyword and is far more generic than the simple Java Bean standard.

The instanceof keyword is used to determine an object type. It takes inheritance into account, so the following is true:
 
ArrayList list = new ArrayList();
boolean example = (list instanceof ArrayList);

So is:
 
ArrayList list = new ArrayList();
boolean example = (list instanceof List);

However, what if the type is dynamic? The following will not compile:
 
ArrayList list = new ArrayList();
Class dynamicClass = java.util.List.class;
boolean example = (list instanceof dynamicClass);

One place you will use this type of code is in a Collection class that only allows a developer-definable type of element to be added to it:
 
TypedList tlist = new TypedList(java.lang.Integer.class);
tlist.add("Test"); // throws runtime IllegalTypeException

The code in TypedList uses the Beans.isInstanceOf method similar to this example:
 
ArrayList list = new ArrayList();
Class dynamicClass = java.util.List.class;
boolean example = Beans.isInstanceOf(list, dynamicClass);

Beans.isInstanceOf takes two arguments: an Object and a Class. It checks to see if the Object is either an instance of Class or that the Object extends or implements the supplied Class. While this type of functionality is relatively easy to create on your own, it is far easier to rely on Sun's own implementation. It saves time, decreases the likelihood of bugs, and reduces the amount of code you need to maintain.
Ramneek Handa
 
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