The problem is that Arrays.asList takes a parameter of T… array. The only applicable T when you pass the int[] is int[], as arrays of primitives will not be autoboxed to arrays of the corresponding object type (in this case Integer[]). So you can do Arrays.asList(new Integer[] {1, 2, 3});.
Yes. JLS §5.6.2 specifies the rules for binary numeric promotion. In part: When an operator applies binary numeric promotion to a pair of operands, each of which must denote a value that is convertible to a numeric type, the following rules apply, in order, using widening conversion (§5.1.2) to convert operands as necessary: If any … Read more
TL;DR Java caches boxed Integer instances from -128 to 127. Since you are using == to compare objects references instead of values, only cached objects will match. Either work with long unboxed primitive values or use .equals() to compare your Long objects. Long (pun intended) version Why there is problem in comparing Long variable with … Read more
You can use the javap tool to see for yourself. Compile the following code: public class AutoboxingTest { public static void main(String []args) { Integer a = 3; int b = a; } } To compile and disassemble: javac AutoboxingTest.java javap -c AutoboxingTest The output is: Compiled from “AutoboxingTest.java” public class AutoboxingTest extends java.lang.Object{ public … Read more
It should be very clear that caching has an unacceptable performance hit — an extra if statement and memory lookup every time you create an Integer. That alone overshadows any other reason and the rest of the agonizing on this thread. As far as responding “correctly” to ==, the OP is mistaken in his assumption … Read more
When you cast the first argument to Object yourself, the compiler will match the method without using autoboxing (JLS3 15.12.2): The first phase (§15.12.2.2) performs overload resolution without permitting boxing or unboxing conversion, or the use of variable arity method invocation. If no applicable method is found during this phase then processing continues to the … Read more
In short, no. There’s no way to get that to compile. Java only defines a limited set of pre-defined boxing conversions. From the JLS, section 5.1.7: Boxing conversion converts expressions of primitive type to corresponding expressions of reference type. Specifically, the following nine conversions are called the boxing conversions: From type boolean to type Boolean … Read more
According to JLS: – The type of a conditional expression is determined as follows: If the second and third operands have the same type (which may be the null type), then that is the type of the conditional expression. If one of the second and third operands is of primitive type T, and the type … Read more
The Big Picture There are two issues at play here: Integer getInteger(String) doesn’t do what you think it does It returns null in this case the assignment from Integer to int causes auto-unboxing Since the Integer is null, NullPointerException is thrown To parse (String) “123” to (int) 123, you can use e.g. int Integer.parseInt(String). References … Read more
There is no autoboxing for arrays, only for primitives. I believe this is your problem.