I am able to reproduce the issue using following sample code: 

TestEnum.java 
-------------------------------------------- 
import java.util.Enumeration; 
import java.util.Hashtable; 
public class TestEnum { 
        public static void main(String[] args) { 
                Hashtable hTable = new Hashtable(); 
                hTable.put("hello", "value"); 
                for (Enumeration enum = hTable.keys();;){ 
                        if(!enum.hasMoreElements()) 
                                break; 
                        enum.nextElement(); 
                } 
        } 
} 
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Compile using "-source 1.4" option 
This code compiles fine with jdk6 but fails with error with jdk8