15.12.2

Examples: Array Access Evaluation Order

EXPRESSIONS

15.12.2   Examples: Array Access Evaluation Order

In an array access, the expression to the left of the brackets appears to be fully

evaluated before any part of the expression within the brackets is evaluated. For

example, in the (admittedly monstrous) expression

a[(a=b)[3]]

, the expression

a

 is fully evaluated before the expression

(a=b)[3]

; this means that the original

value of

a

 is fetched and remembered while the expression

(a=b)[3]

 is evalu 

ated. This array referenced by the original value of

a

 is then subscripted by a value

that is element

3

 of another array (possibly the same array) that was referenced by

b

 and is now also referenced by

a

.

Thus, the example:

class Test {

public static void main(String[] args) {

int[] a = { 11, 12, 13, 14 };

int[] b = { 0, 1, 2, 3 };

System.out.println(a[(a=b)[3]]);

}

}

prints:

14

because the monstrous expression's value is equivalent to

a[b[3]]

 or

a[3]

 or

14

.

If evaluation of the expression to the left of the brackets completes abruptly,

no part of the expression within the brackets will appear to have been evaluated.

Thus, the example:

class Test {

public static void main(String[] args) {

int index = 1;

try {

skedaddle()[index=2]++;

} catch (Exception e) {

System.out.println(e + ", index=" + index);

}

}

static int[] skedaddle() throws Exception {

throw new Exception("Ciao");

}

}

prints:

java.lang.Exception: Ciao, index=1

because the embedded assignment of

2

 to

index

 never occurs.

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