If you need different behaviour when you’re dealing with a value-type then you’re obviously going to need to perform some kind of test. You don’t need an explicit check for boxed value-types, since all value-types will be boxed** due to the parameter being typed as object. This code should meet your stated criteria: If value … Read more
However, variant c does not, probably because the new function takes only values of the same type which is not the case since Fooer != i32. No, it’s because there is no new function for Box<dyn Fooer>. In the documentation: impl<T> Box<T> pub fn new(x: T) -> Box<T> Most methods on Box<T> allow T: ?Sized, … Read more
Jon’s point is true, but as a side note there is one slight exception to the rule; generics. If you have where T : ISomeInterface, then this is constrained, and uses a special opcode. This means the interface can be used without boxing. For example: public static void Foo<T>(T obj) where T : ISomeInterface { … Read more
Internal Java implementation and could not be configured, the range is from -128 to 127. You can check Javadocs or simply take a look at sources: public static Integer valueOf(int i) { final int offset = 128; if (i >= -128 && i <= 127) { // must cache return IntegerCache.cache[i + offset]; } return … Read more
No, it does not exist. Actually, it was explicitly not implemented so as not to clutter the Stream API with tons of classes for every primitive type. Quoting a mail from Brian Goetz in the OpenJDK mailing list: Short answer: no. It is not worth another 100K+ of JDK footprint each for these forms … Read more
The Short Answer The key point is this: == between two reference types is always reference comparison More often than not, e.g. with Integer and String, you’d want to use equals instead == between a reference type and a numeric primitive type is always numeric comparison The reference type will be subjected to unboxing conversion … Read more
Boxed values are data structures that are minimal wrappers around primitive types*. Boxed values are typically stored as pointers to objects on the heap. Thus, boxed values use more memory and take at minimum two memory lookups to access: once to get the pointer, and another to follow that pointer to the primitive. Obviously this … Read more
Because of this code in Integer.valueOf(int): public static Integer valueOf(int i) { if(i >= -128 && i <= IntegerCache.high) return IntegerCache.cache[i + 128]; else return new Integer(i); } Explanation: Integer integer1 = 127 is a shortcut for Integer integer1 = Integer.valueOf(127), and for values between -128 and 127 (inclusive), the Integers are put in a … Read more
Since Java 8 you can now use streams for that: long[] arr = { 1, 2, 3, 4 }; List<Long> list = Arrays.stream(arr).boxed().collect(Collectors.toList());
Why To have a unified type system and allow value types to have a completely different representation of their underlying data from the way that reference types represent their underlying data (e.g., an int is just a bucket of thirty-two bits which is completely different than a reference type). Think of it like this. You … Read more