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Wrapper classes
Why does the following code compile?
if Double is a class, why am I able to assign the return value of test() to a double?
if Integer is a class, why am I able to pass just 12, and not "new Integer(12)"?
public static void main(String[] args) {
double x = test(12);
}
public static Double test(Integer a) {
a = 13;
return new Double(34.12);
}
Re: Wrapper classes
See Autoboxing
Re: Wrapper classes
The compiler has a feature: autoboxing that will do many conversions so that you don't have to understand what needs to be done or what was done to change code into legal Java code.
It allows sloppy/lazy programmers to write code that normally wouldn't compile as coded. There are many cases where autoboxing fools programmers and makes for bugs in the code until the programmer understands what the compiler has done to him.
One example:
The arg for the first arg is autoboxed to Integer(123). The second arg is the index of the element to be removed. It is not autoboxed.anArrayListRef.add(123); // add an object to an arraylist anArrayListRef.remove(123); // remove that element from the arraylist
If you don't understand my answer, don't ignore it, ask a question.
Re: Wrapper classes
so this is for collection section ?
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