Getting the names of all classes

Hi,
I want to write a Java editor with code completion. Is there a way to get all the class names available in the installed Java run time environment.
Does the reflection API provides a way to do it.
Thanks a lot,
Chamal.

You can also look at JPDA (should be documented as part of your JDK under 'Tool Support' of the documents index), and the JDI api VirtualMachine.allClasses() method.
That will return the name of all loaded classes, which will not be the same as all classes on the path, as it includes any dynamically created classes, and excludes any classes on the path not loaded.
Pete

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Message was edited by:
johnminkjan

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SYS                            DBMS_OUTPUT                    GET_LINE
SYS                            DBMS_OUTPUT                    NEW_LINE
SYS                            DBMS_OUTPUT                    PUT_LINE
SYS                            DBMS_OUTPUT                    PUT_LINE
SYS                            DBMS_OUTPUT                    PUT
SYS                            DBMS_OUTPUT                    PUT
SYS                            DBMS_OUTPUT                    DISABLE
SYS                            DBMS_OUTPUT                    ENABLE
9 rows selected.
"or"
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Hi Alexandr,
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AS

How to get the name of a field without specifying it as a string (somehow v

Is it possible to get the name of a field (or method) somehow via the class in which it is declared?
The reason why I ask is, that quite often the name of a field is important, because the name is the anchor for further processing, like for example when using reflection (e.g. Class.getfield(NameOfTheField)).
Assume you have class FooSimple with the field String firstName.
Now you would do something like this:
Class<FooSimple> cls = FooSimple.class;
Field f = cls.getField("firstName");
The problem is, that the string firstName is kind of hard coded. When the name of the field in class FooSimple changes (e.g. to theFirstName), the invocation will not work anymore when you forget to change the string too.
I think it would be very helpful to have access to the name of the field directly via the class by doing something like this.
Class<FooSimple> cls = FooSimple.class;
Field f = cls.getField(FooSimple.firstName.fieldName);
The Java Compiler would then resolve FooSimple.firstName.fieldName to the string firstName. When later the name of the field is changed, the IDE would change the name everywhere where it is used. So if the name of the field would be changed to theFirstName the IDE would also change the statement to
Class<FooSimple> cls = FooSimple.class;
Field f = cls.getField(FooSimple.theFirstName.fieldName);
A technique like this would be in my opinion much more safety and more generic.
Any ideas?
Best Regards.

Well, I think the discussion is going in a wrong direction because the original issue was not to discuss if it is worth coding some helper classes or a framework or that like. Let me bring it back to my original point.
Basically you can reduce my original question to this:
Currently it is possible to use the reflection API on a class level without specifying the name of the class with a string constant.
My issue is, that I think it would be a nice extension for Java, if the same would be possible for field variables of a Java class. Currently the only way you can do this is by specifying the field variable with a string constant.
Let me bring some motivations which brought me to this issue.
Assume you have an entity bean which represents a DB table and you use Java Persistence (either JPA or something like Hibernate). Then you would have a class looking like this (very simple sample to make this reply shorter).
@Entity
@Table(name = "PERSON")
public class Person implements Serializable {
@Column(name = "NAME")
private String name;
// constructor, getter, setter, etc. not listed here
}The whole issue of the design of JPA is, that such entity beans represent the mapping between the object model and the DB model, the mapping is expressed with annotations.
Okay, now lets assume you write a query in Query Language, e.g.
String sql = select p from Person p where name = :name;name is the name of the field variable, :name is the parameter you later set with Query.setParameter method.
What is not so nice is the fact, that you use the name of the class and the name of the field variables hardcoded to construct the query. Now you could think that basically this information is part of your entity class. First you start with the name of the class (i.e. the table name) to decouple this hardcoding.
You could write instead:
String sql = select p from + Person.class.getSimpleName() + p where name = :name;This is really nice, because whenever you change the name of your Person class, this change happens automatically for the sql statement as well.
I think the next thoughts are obvious, now, since you have decoupled the hardcoded part of the name of the class, you would like to do the same for the names of the field variables. But now you are stuck, there is no way to do this using a similar technique like for the name of the class. Either you stay with the query as it is now, or, to make it a little bit better, you code string constants for the field variables and use them. This issue brought me to the point that I think it would be nice to have the possibility to get the name of a field variable in a similar way as you can get it for the name of the class.
Conceptually it is just to go one level deeper, i.e.
first level is to get the name of a class
second level is to get the name of the field variable of a class.
Another sample would be, if you want to code something by using reflection. You have perfectly access to the reflection API starting at the class level like Person.class.allTheNiceReflectionMethods. There is no need to specify the class first with a string constant first, you directly start with the class, you can even be generic and just work on the Class.class level and still have access to all these nice methods to get out the information you need.
But if you need to start with a very specific field variable (like in the sample above), you must go by using a string constant like Person.class.getDeclaredField(name).
So basically I think that there exist already millions of lines of Java code where a field variable is specified for further processing, especially in combination with the reflection functionality and everywhere the field variables are specified by these string constants in double quotes. I would assume, that everyone has the same problem, once changing the name of the field variable means to take care that also the content of the string which specifies the name of the field variable is changed.
I am wondering why one of the replies commented, why the name of a field variable is changed, it sounds to me that this is something which basically never happens. I dont know, I think that this happens actually quite often and thanks to all these nice IDEs and their rename feature this is usually no problem. From time to time names of classes change, name of field change, yes, they are often even completely rewritten, new field variables come in some are deleted, whatever it is. The way I currently can access the name of a class makes the code safer, because when I consequently go with Class.class.getSimpleName I always know, that when I rename the class all these statements are changed too If I delete such a class, I at least get a compile error.
My very simple issues is, that I think it would be nice to have the same comfort not only on a class level but also on the level of field variables, nothing more, nothing less.
To be honest, I have not browsed the forum yet if such an issue was already raised by other people (I will do this now), but somehow it is hard to imagine, that I am the first one.
Best regards.

Getting the names of all classes

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