Solved

warning: [unchecked] unchecked cast

Posted on 2013-11-14
8
501 Views
Last Modified: 2013-11-14
Hi,

I get this compile error when I try to compile my class with -Xlint:unchecked

warning: [unchecked] unchecked cast
		E[] newData = (E[]) new Object[capacity];
		                    ^
  required: E[]
  found:    Object[]
  where E is a type-variable:
    E extends Object declared in class ArrayList

Open in new window

If I compile without -Xlint, I get a warning, but no error, and the program works.

But it makes me nervous. Is there some way to 'fix' this to make -Xlint happy?

Thanks.
0
Comment
Question by:Kyle Hamilton
  • 4
  • 4
8 Comments
 
LVL 26

Expert Comment

by:dpearson
ID: 39648768
Have you tried:

E[] newData = new E[capacity] ;

Doug
0
 
LVL 25

Author Comment

by:Kyle Hamilton
ID: 39648792
so, putting this in front of the constructor was supposed to eliminate this message, but it had no effect on the message I'm getting in the console:

@SuppressWarnings("unchecked")

Open in new window


I still get this message:

Note: ArrayList.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.

Open in new window


oh well, apparently this is not a big deal. If anyone has any input, I would appreciate it.

Thanks.
0
 
LVL 25

Author Comment

by:Kyle Hamilton
ID: 39648801
Hi Doug,

according to the book,
E[] newData = new E[capacity] ;

Open in new window

would give ma an "invalid generic type" and won't compile.
0
 
LVL 26

Expert Comment

by:dpearson
ID: 39648851
Ah - didn't know it was generic.

That's certainly harder.  If you have access to the class itself you can do:

E createObject(Class<E> clazz)
{
      return clazz.newInstance();
}

To create a typesafe instance of the class.  (If we can get that working, then need to figure out how to extend it to the whole array).

But to do that you need to pass in E.class at the time of the call to the generic method/class - can't look it up later on inside the method because E will have had its type erased.

Is that an option?

Doug
0
Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

 
LVL 25

Author Comment

by:Kyle Hamilton
ID: 39648934
Ok, so I have this in my class:

private E createObject(Class<E> clazz) throws Exception{
		return clazz.newInstance();
	}

Open in new window


and now this:

E newData = new E[capacity];

Open in new window


now the error is:

error: generic array creation
		E newData = new E[capacity];

Open in new window


Would it be helpful if I posted the whole class code?
0
 
LVL 26

Accepted Solution

by:
dpearson earned 500 total points
ID: 39648973
OK - it looks like the one you really want is
java.lang.reflect.Array.newInstance()

which allows you to create a new array of objects of a specific type, like E.class.

More docs on it here:
http://docs.oracle.com/javase/7/docs/api/java/lang/reflect/Array.html#newInstance(java.lang.Class, int)

And a bit of tutorial on the whole thing here:
http://docs.oracle.com/javase/tutorial/reflect/special/arrayInstance.html

Although I'm not sure this will ultimately clear the warning - as it seems
java.lang.reflect.Array.newInstance()
returns type Object
instead of type E[]
...

which looks wrong to me :)

Doug
0
 
LVL 25

Author Closing Comment

by:Kyle Hamilton
ID: 39649010
Thank you. much appreciated.

I better get outta this rabbit hole, for now.

Once I pass Level 1, I'll revisit this :) I think for now, I'm gonna live with the warning.

Cheers,
Koza
0
 
LVL 26

Expert Comment

by:dpearson
ID: 39649168
Haha - fair enough :)

Doug
0

Featured Post

Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

For customizing the look of your lightweight component and making it look opaque like it was made of plastic.  This tip assumes your component to be of rectangular shape and completely opaque.   (CODE)
An old method to applying the Singleton pattern in your Java code is to check if a static instance, defined in the same class that needs to be instantiated once and only once, is null and then create a new instance; otherwise, the pre-existing insta…
Viewers learn about the third conditional statement “else if” and use it in an example program. Then additional information about conditional statements is provided, covering the topic thoroughly. Viewers learn about the third conditional statement …
Viewers will learn about the different types of variables in Java and how to declare them. Decide the type of variable desired: Put the keyword corresponding to the type of variable in front of the variable name: Use the equal sign to assign a v…

864 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

19 Experts available now in Live!

Get 1:1 Help Now