Where's org.eclipse.core.runtime.Assert available?

Exception in thread "main" java.lang.NoClassDefFoundError: org/eclipse/core/runtime/Assert

Seems the runtime.jar has no org.eclipse.core.runtime.Assert in it:

Am I using a wrong ver开发者_开发百科sion though it's shipped with my eclipse?

UPDATE

I don't have Plugin Development Perspective:

It's in org.eclipse.equinox.common.

To check out which JAR a class belongs to you can use "Open Type" dialog - just press Ctrl+Shift+T in Plugin Development Perspective and type the class name.