Will the above code first wrap the int literal 8 in an Integer and then assign its reference to variable ob? Yes. (Or rather, it will box the int value into an Integer object, and then assign the reference to the variable ob. The fact that the integer value is a literal is irrelevant here, … Read more
There are obviously 3 questions here so lets tackle them one by one: How exactly do I expect that list methods will work when I’m expecting an List of Integer and getting a List of int[] ? Well, List methods will work exactly as expected, a List<T> is a list of types T. Here T … Read more
You can’t do that in a foreach loop. for (int i=0; i<copyArray.length;i++) copyArray[i] /= 2; Else you are not assigning it back into the array. Integer objects are immutable by the way so can’t modify them (creating new ones though). Updated from comment: Beware though that there are a few things going on, autoboxing/unboxing for … Read more
I guess it’s related to bug #6886431, which seems to be fixed in OpenJDK 7 as well. The problem is that JLS 15.12.2.5 Choosing the Most Specific Method says that one method is more specific than another one when types of formal parameters of the former are subtypes of formal parameters of the latter. Since … Read more
The return type of the conditional expression b ? d1.doubleValue : d2 is double. A conditional expression must have a single return type. Following the rules for binary numeric promotion, d2 is autounboxed to a double, which causes a NullPointerException when d2 == null. From the language spec, section §15.25: Otherwise, if the second and … Read more
I first tought your question was a dupe of What code does the compiler generate for autoboxing? However, after your comment on @ElliottFrisch I realized it was different : I know the compiler behaves that way. I’m trying to figure out whether that behavior is guaranteed. For other readers, assume that “behaves that way” means … Read more
Boxing is when you convert a primitive type to a reference type, un-boxing is the reverse. Casting is when you want one type to be treated as another type, between primitive types and reference types this means an implicit or explicit boxing operation. Whether it needs to be explicit is a language feature.
If you don’t mind using a 3rd party library, commons-lang has the ArrayUtils type with various methods for manipulation. Double[] doubles; … double[] d = ArrayUtils.toPrimitive(doubles); There is also the complementary method doubles = ArrayUtils.toObject(d); Edit: To answer the rest of the question. There will be some overhead to doing this, but unless the array … Read more
It is defined in the JLS #15.21.1: If the operands of an equality operator are both of numeric type, or one is of numeric type and the other is convertible (§5.1.8) to numeric type, binary numeric promotion is performed on the operands (§5.6.2). And JLS #5.6.2: When an operator applies binary numeric promotion to a … Read more
Ternary expressions, like any expression, have a type that is determined by the compiler. If the two sides of the ternary expression have what looks like different types, then the compiler will try and find a common base type using the least ambiguous of the two options. In your case, the -1 is least ambiguous, … Read more