up vote 1 down vote favorite 
java.lang.ClassCastException: java.lang.Float cannot be cast to java.lang.String

I am getting this exception in follwing code: 

String colValue= (String)data_ForSave.elementAt(r).get(ColValindex);

Where ForSave is a vector of String containing table values, I can not understant why this exception is thrown.

Below is the full Stack Trace of the excption.

Stack Trace Of Exception 

java.lang.ClassCastException: java.lang.Float cannot be cast to java.lang.String
at Utilities.Utility.DataHeaderMapping(Utility.java:1122)
at jewelleryerpapplication.GUI.ProductsInformation.jbtnSaveActionPerformed(ProductsInformation.java:4222)
at jewelleryerpapplication.GUI.ProductsInformation.access$1500(ProductsInformation.java:40)
at jewelleryerpapplication.GUI.ProductsInformation$37.actionPerformed(ProductsInformation.java:3292)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6505)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at java.awt.Component.processEvent(Component.java:6270)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4861)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2713)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:707)
at java.awt.EventQueue.access$000(EventQueue.java:101)
at java.awt.EventQueue$3.run(EventQueue.java:666)
at java.awt.EventQueue$3.run(EventQueue.java:664)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:680)
at java.awt.EventQueue$4.run(EventQueue.java:678)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:677)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:211)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:128)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:117)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:113)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:90)
Row   : 0

Lots of thanks in advance for providing an answer as i am stuck with that.

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up vote 4 down vote accepted

From your comment it appears you are using an incorrect generic type.

e.g.

Vector g = new Vector();
List list = new ArrayList();
list.add(1.0f);
g.add(list);

Vector<List<String>> grid = g; // incorrect cast, but only a warning.
String s = g.elementAt(0).get(0); // throws a class cast exception.

BTW: I have no idea why you would use a combination of elementAt(index) and get(index) as these are the old (pre Java 1.2) and newer styles (post Java 1.2) unless Swing requires it. ;)

I would use this to reverse an incorrect generic type, although fixing the type would be better.

List list = (List) data_ForSave.elementAt(r);
String colValue= String.valueOf(list.get(ColValindex));

as you cannot cast a Float to a String. You can instead turn it into a String.

share|improve this answer
    
Your solution generating the same error. Thanks – Syed Muhammad Mubashir Mar 21 '12 at 12:47
    
In that case, the cast is redundant and the generic type for your collection is incorrect. I have edited my solution. – Peter Lawrey Mar 21 '12 at 12:50
    
Vector<Vector<String>> data_ForSave = new Vector<Vector<String>>(); is my declaration – Syed Muhammad Mubashir Mar 21 '12 at 12:55
    
So in this collection you have added a Float using an unchecked operation. When you try to retrieve it, there is an exception. I have added a workaround if you cannot find where the Float is being added, but its better to fix it so this doesn't happen. – Peter Lawrey Mar 21 '12 at 12:59
    
Great thanks to you for taking the time as your new answer solve my problem.(:- – Syed Muhammad Mubashir Mar 21 '12 at 13:12
up vote 4 down vote

The problem is that data_ForSave.elementAt(r).get(ColValindex) is returning a Float, not a String. If you want to format it as a string — e.g., you want 3.45 to be converted to "3.45", then you can write:

String colValue= data_ForSave.elementAt(r).get(ColValindex).toString();
share|improve this answer
    
Your solution generating the same error when i applied. Thanks – Syed Muhammad Mubashir Mar 21 '12 at 12:52
    
Even if it's specified as a Vector<String>, you might be doing some evil unsafe casting somewhere to make it contain a Float. The exception you're getting proves the vector contains a Float, whether or not it's supposed to; if it's not supposed to contain floats, then that's what you need to debug. – Louis Wasserman Mar 21 '12 at 12:59
    
I find it hard to believe that this solution did not work. The answer is correct in that Java will not allow you to directly cast a Float object to a String. Try the following statement: String s = new Float(1.23).toString(); This should work fine, and is basically what the answer is telling you to do. However, the statement String s = (String) new Float(1.23) will result in a CastClass exception. – Howard Schutzman Mar 21 '12 at 18:22
    
@HowardSchutzman: The reason it didn't work is that generics in Java use "type erasure", whereby type parameters don't exist at runtime. The OP had inserted a Float into an object of runtime type Vector, and was trying to retrieve the element via a reference with compile-time type Vector<String> (thereby triggering an implicit cast to String). The explicit String cast was a red herring. – ruakh Mar 21 '12 at 18:29
up vote 1 down vote

Change the declaration of data_ForSave to

Vector<String> data_ForSave = new Vector<String>();

and your IDE should guide you to the source of this problem through errors or warnings.

share|improve this answer
    
When the OP wrote, "ForSave is a vector of String containing table values", that meant, "ForSave is a vector of table values that contain Strings". – ruakh Mar 21 '12 at 12:52
    
Yes obviously Vector<Vector<String>> data_ForSave = new Vector<Vector<String>>(); is my declaration – Syed Muhammad Mubashir Mar 21 '12 at 12:54
    
Yikes - "string containing table values" - I (mis)understood "string(s) containing table values". Anyway - Vector should be parametized. – Andreas_D Mar 21 '12 at 14:11
up vote 0 down vote

As per your comment, what I see is ForSave vector is not generic. So, when you trying to cast it without instanceof validation, it will give you a error. What I suggest is:

String colValue = "";
if(data_ForSave.elementAt(r).get(ColValindex) instaceof Float)
   colValue = String.valueOf(data_ForSave.elementAt(r).get(ColValindex));
else
   colValue = data_ForSave.elementAt(r).get(ColValindex);
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