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/* package whatever; // don't place package name! */
 
import java.util.*;
import java.lang.*;
import java.io.*;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		List<? super Number> test = new ArrayList<Object>();
        test.add(new Double(1.2));
        test.add(new Integer(1));
        test.add(new Float(2.3));
        test.add(new Object());
        if(test.get(0) instanceof Integer){
        	System.out.println("Integer");
        } else if(test.get(0) instanceof Double){
        	System.out.println("Double");
        }
	}
}

Main.java:16: error: no suitable method found for add(Object)
        test.add(new Object());
            ^
    method Collection.add(CAP#1) is not applicable
      (argument mismatch; Object cannot be converted to CAP#1)
    method List.add(CAP#1) is not applicable
      (argument mismatch; Object cannot be converted to CAP#1)
  where CAP#1 is a fresh type-variable:
    CAP#1 extends Object super: Number from capture of ? super Number
Note: Some messages have been simplified; recompile with -Xdiags:verbose to get full output
1 error

Standard output is empty