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  1. /* package whatever; // don't place package name! */
  2.  
  3. import java.util.*;
  4. import java.lang.*;
  5. import java.io.*;
  6.  
  7. /* Name of the class has to be "Main" only if the class is public. */
  8. class Ideone
  9. {
  10. public static void main (String[] args) throws java.lang.Exception
  11. {
  12. Hashtable<String, Integer> tab = new Hashtable<>();
  13. tab.put("A", new Integer(42));
  14.  
  15. // Unchecked conversion ... gives a compiler warning, but you can
  16. // ignore it, or suppress it.
  17. Hashtable<String, String> bad = (Hashtable<String, String>) tab;
  18.  
  19. // String res = tab.bad("A"); // Ooops!
  20. System.out.println("abc");
  21. }
  22. }
Compilation error #stdin compilation error #stdout 0s 0KB
stdin
Standard input is empty
compilation info
Main.java:17: error: incompatible types: Hashtable<String,Integer> cannot be converted to Hashtable<String,String>
	 Hashtable<String, String> bad = (Hashtable<String, String>) tab;
	                                                             ^
1 error
stdout
Standard output is empty