Type Casting String to NumberOnlyBuildLabel

[Saurabh Garg]

Hi I need To typecast String to NumberOnlyBuildLabel to provide its value to DataSetBuilder.

What I have done was as below but I failed  during execution i am getting this exception.

Unable to  cast java.lang.String to hudson.util.ChartUtil$NumberOnlyBuildLabel 

What I am doing Is 

String Build ="121"

Object build=(Object)Build;

Label=(NumberOnlyBuildLabel) build;

Is there any other way around