differences between a primitive type and a class type

[Serhat Duygun]

Hi, everyone,

i am trying to understand that differences between a primitive type and a class type have an impact, i know if google it i can get plenty of documentation about that, but please take look at my exemple and explain to me why above code result is

i = 1,  iArr[0] = 2

why "i" is not "2" i really confuse

Thank You

public class zindik {

	public static void main(String args[]){
		int i = 1;
		int [] iArr = {1};
		System.out.println(iArr[0]);
		incr(i);
		incr(iArr);	
		System.out.println("i = "+i+",  "+ "iArr[0] = "+iArr[0]);
		
	}
	public static void incr(int n){ n++;}
	public static void incr(int [] n){n[0]++;}
	
}

[Jeff Verdegan]

The reason that main's i is not incremented is because Java passes all parameters by value. A result of this is that when you change the value of a method parameter inside that method, the change only affects the method's copy of that variable, and is not seen by the caller.

"Wait," you might say. "Why then can main see the change to the iArr variable?" The answer is: It can't. That variable's value isn't changing. What's chaning is the contents of the object (an array) that both main's iArr and incr's n point to. The iArr reference variable's value was copied, so now we have to independent reference variables pointing to the same object. We're not changing the value of either of those variables, just the inside of the object they point to.

void foo(int i, Bar bar, something[] arr) {

i = 1; // not seen by caller
bar = something; // not seen by caller
arr = something; // not seen by caller

bar.someField = something; // seen by caller
arr[index] = something; // seen by caller

So it's the difference between, on one hand X = something and, on the other hand, X.field = something or X[index] = something.

[Serhat Duygun]

Thank you so much. it helped me a lot.