A DESCRIPTION OF THE PROBLEM :
For the conditional statement, there seems to be some sort of bug that is only showing up in Java 11 for some reason.


For this source code:


  public static Object returnObject(Object n) {
    return n instanceof Number ? ((Number) n).longValue() : Double.NaN;
  }

  public static Object returnObject2(Object n) {
    if (n instanceof Number) {
      return ((Number) n).longValue();
    } else {
      return Double.NaN;
    }
  }


We can see that the bytecode is different:


  public static java.lang.Object returnObject(java.lang.Object);
    Code:
       0: aload_0
       1: instanceof #15 // class java/lang/Number
       4: ifeq 18
       7: aload_0
       8: checkcast #15 // class java/lang/Number
      11: invokevirtual #16 // Method java/lang/Number.longValue:()J
      14: l2d
      15: goto 21
      18: ldc2_w #17 // double NaNd
      21: invokestatic #10 // Method java/lang/Double.valueOf:(D)Ljava/lang/Double;
      24: areturn

  public static java.lang.Object returnObject2(java.lang.Object);
    Code:
       0: aload_0
       1: instanceof #15 // class java/lang/Number
       4: ifeq 18
       7: aload_0
       8: checkcast #15 // class java/lang/Number
      11: invokevirtual #16 // Method java/lang/Number.longValue:()J
      14: invokestatic #4 // Method java/lang/Long.valueOf:(J)Ljava/lang/Long;
      17: areturn
      18: ldc2_w #17 // double NaNd
      21: invokestatic #10 // Method java/lang/Double.valueOf:(D)Ljava/lang/Double;
      24: areturn


Note that in instruction 14 of returnObject, there is a cast from long to double. This shows up in the tests where we are expecting a long but it is actually a double that is returned. I do not expect this cast to be there at all as I think Long is a valid return type for returnObject.

I've reproduced this problem with 11.0.5 and 1.8.0_172.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
12
false
true
false
ACTUAL -
12.0
true
false
true


---------- BEGIN SOURCE ----------
public class Test {

  public static void main (String[] args) {
    Object o = returnObject(Long.valueOf(12));
    System.out.println(o);
    System.out.println(o.equals(Double.valueOf(12.0)));
    System.out.println(o instanceof Long);
    System.out.println(o instanceof Double);
  }

  public static Object returnObject(Object n) {
    return n instanceof Number ? Long.valueOf(((Number) n).longValue()) : Double.NaN;
  }

  public static Object returnObject2(Object n) {
    if (n instanceof Number) {
      return ((Number) n).longValue();
    } else {
      return Double.NaN;
    }
  }

}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
The workaround is to split this up into an explicit if statement as shown in the source code and related bytecode.