Let's take a look at the following code:
public Class Program{
public static void main(String[] args){
int i = 0;
int[] a = {1,2};
a[i] = i = 2;
System.out.println(i + " " + a[0]+ " "+a[1]);
}
}
What is the output from the above code?
The output is:
2 2 2
You may raise some questions: "When does i get a value 2?",
"Why doesn't it use the same value (i=2) for a[i]
(which should actually give an ArrayOutOfBoundsException
Exception)?", and so on.
The reason no ArrayIndexOutOfBoundsException is thrown is
because each of the operands is evaluated from left to right. Basically
the array reference is evaluated first then the rest of the expression
is done according to the rules in the "15.26.1
Simple Assignment Operator =" of Java Language Specification 3rd
Edition. We first evaluate a[i] while i is still 0.
Then the assignment takes place after the leftmost operand is
evaluated. After the assignment operator takes over, it changes the
value of i to 2 and then assign i variable value to a[0].
Hence, a[0] obtains a value of 2 and no an ArrayIndexOutOfBoundsException
is thrown.
The assignment is performed from right to left, but operand
evaluation is evaluated from left to right.