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java reflection element to a list by using reflection

Hi,

I am reading below link
http://tutorials.jenkov.com/java-reflection/index.html

I have not clearly understood about below lines

For instance, when mapping objects to tables in a database at runtime, like Butterfly Persistence does. Or, when mapping the statements in a script language to method calls on real objects at runtime, like Butterfly Container does when parsing its configuration scripts.

Is java reflection only from j2se6 onwards. Where to find which version has which new features at a glance and their simple explanation.

How is propertyutils used in reflection in adding element to a list by using reflection. http://commons.apache.org/proper/commons-beanutils/apidocs/org/apache/commons/beanutils/PropertyUtils.html#getPropertyDescriptor(java.lang.Object

Any detailed example on that.

I also referred below link
http://stackoverflow.com/questions/37628/what-is-reflection-and-why-is-it-useful

I did not understand below statements

va's static typing system isn't really designed to support this unless the object conforms to a known interface, but using reflection, your code can look at the object and find out if it has a method called 'doSomething' and then call it if you want to.

So, to give you a code example of this in Java (imagine the object in question is foo) :

Method method = foo.getClass().getMethod("doSomething", null);
method.invoke(foo, null);One very common use case in Java is the usage with annotations. JUnit 4, for example, will use reflection to look through your classes for methods tagged with the @Test annotation, and will then call them when running the unit test.

please advise
Any links resources ideas highly appreciated. Thanks in advance

ASKER CERTIFIED SOLUTION

CPColin

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gudii9

ASKER

I did not get what it mean by 'knowing object information at runtime' can you please explain what and why and how, when we do it.

CPColin

When you're developing code, you can see all the methods and variables that are available in classes you're using. Like, you know that the method String.trim() is available to you when you're working with an instance of the String class.

Reflection is used when your code does not know what kind of objects it's working with. This happens when the type of object your code has to work with is determined at runtime. This especially happens when writing libraries.

You're usually safer when you design your code in a way that avoids reflection, for the most part. Basically, unless you're forced to use it, try not to.

gudii9

ASKER

Reflection is used when your code does not know what kind of objects it's working with. This happens when the type of object your code has to work with is determined at runtime. This especially happens when writing libraries.

What would be scenario when to use this in practical world. I do not write libraries.

I see code as below

PropertyUtils.getPropertyDescriptor(obj, fieldName).getWriteMethod().invoke(obj, list);

What is the meaning of above code while parsing a text document which has not only primitives but also list kind of objects before sending to one other system.
please advise

CPColin

What would be scenario when to use this in practical world. I do not write libraries.

I mentioned this already in my previous comment. You would use reflection when you don't know what kind of object you're dealing with until your code actually runs. If you have no situations in your code where that applies, then you don't need reflection.

What is the meaning of above code...

You will have to read the Javadocs for that class; I am not very familiar with it. You may also want to take that part of the discussion over to your "PropertyUtils java" question.

gudii9

ASKER

What are these ButerFly Component and ButterFly Persistence mentioned in the link. Please advise

gudii9

ASKER

How the reflection on class, method, field are different. Please advise

gudii9

ASKER

Any practical example to understand this reflection concept end to end better with set up on eclipse. please advise

gudii9

ASKER

Using reflection for debugging and testing, as JUnit does, is a pretty nice benefit, because the code doing the hard work can stay contained in your JUnit tests, instead of polluting your main code.

Can you please elaborate on this.

CPColin

Not really. I made that comment over a month ago and I no longer remember what I was talking about. In general, 99.9% of code does not need reflection. If you're not sure if you need it, you probably don't.

If you have a specific question about reflection, I'll try to answer it.