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
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
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());
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
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