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Message:
Mutable versus Immutable Objects
Posted by Bill Venners on April 23, 2000 at 8:07 PM
> Hi all, > with the following attempt to transfer a program I failed. The Java program prints 'null', not 33. Is there a way, which leads to the correct result? But I do not mean programs, which int as return value supplies or which int a into an array of the length one pack. That already occurred to me.
> If there is no solution: Why may one make something in Java with arrays, what is forbidden with normal objects?
> Best greetings Lutz
> /************ C code ************************ > int x; > void subprog(int* a)
> {
> *a = 33;
> return;
> } > void main(void)
> {
> subprog(&x);
> printf("%d\n", x);
> } > ************* Faulty Java translation ******/ > public class Stupid
> {
> static Integer x;
> static public void a(Integer y)
> {
> y = new Integer(33);
> }
> public static void main(String[] args)
> {
> a(x);
> System.out.println(x);
> }
> } To your question: If there is no solution: Why may one make something in Java
with arrays, what is forbidden with normal objects? Class Integer happens to be immutable. Once it is created with
a value, it can't change. Arrays are always mutable. You can
easily create a class that is mutable that allows you to do
what you want, such as:
class MutableInteger { private int val; MutableInteger(int val) {
this.val = val;
} int getVal() {
return val;
} void setVal(int newVal) {
val = newVal;
}
}
Kind of an ugly class because it is so data-oriented, but I
believe that should answer your question. bv
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