The difference is that the explicit type of the returnsNull() method affects the static typing of the expressions at compile time: E1: `true ? returnsNull() : false` – boolean (auto-unboxing 2nd operand to boolean) E2: `true ? null : false` – Boolean (autoboxing of 3rd operand to Boolean) See Java Language Specification, section 15.25 Conditional … Read more
When in doubt, check the bytecode: Integer n = 42; becomes: 0: bipush 42 2: invokestatic #16 // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer; 5: astore_1 So in actuality, valueOf() is used as opposed to the constructor (and the same goes for the other wrapper classes). This is beneficial since it allows for caching, and doesn’t force the creation … Read more
The compiler interprets null as a null reference to an Integer, applies the autoboxing/unboxing rules for the conditional operator (as described in the Java Language Specification, 15.25), and moves happily on. This will generate a NullPointerException at run time, which you can confirm by trying it.
Some context is required to fully understand the main reason behind this. Primitives versus classes Primitive variables in Java contain values (an integer, a double-precision floating point binary number, etc). Because these values may have different lengths, the variables containing them may also have different lengths (consider float versus double). On the other hand, class … Read more
In Joshua Bloch’s Effective Java, Item 5: “Avoid creating unnecessary objects”, he posts the following code example: public static void main(String[] args) { Long sum = 0L; // uses Long, not long for (long i = 0; i <= Integer.MAX_VALUE; i++) { sum += i; } System.out.println(sum); } and it takes 43 seconds to run. … Read more
Streams In Java 8+ you can make a stream of your int array. Call either Arrays.stream or IntStream.of. Call IntStream#boxed to use boxing conversion from int primitive to Integer objects. Collect into a list using Stream.collect( Collectors.toList() ). Or more simply in Java 16+, call Stream#toList(). Example: int[] ints = {1,2,3}; List<Integer> list = Arrays.stream(ints).boxed().collect(Collectors.toList()); … Read more
The true line is actually guaranteed by the language specification. From section 5.1.7: If the value p being boxed is true, false, a byte, a char in the range \u0000 to \u007f, or an int or short number between -128 and 127, then let r1 and r2 be the results of any two boxing conversions … Read more
No, == between Integer, Long etc will check for reference equality – i.e. Integer x = …; Integer y = …; System.out.println(x == y); this will check whether x and y refer to the same object rather than equal objects. So Integer x = new Integer(10); Integer y = new Integer(10); System.out.println(x == y); is … Read more