About Question enthuware.ocajp.i.v7.2.971 :

[jinwchun]

public class TestClass{    
public static void main(String args[] ){       
int i = 0 ;       
int[] iA = {10, 20} ;       
iA = i = 30 ;       
System.out.println(""+ iA[ 0 ] + " " + iA[ 1 ] + "  "+i) ;     
}
}

Can anyone explain why iA = i = 30 doesn't get processed as follows?
iA[0] = i = 30 ----> iA[0] = 0 = 30
If the left side operand gets evaluated first, the iA[0] should be assigned i which was initially set 0 before i = 30 gets evaluated, correct?

[admin]

This is explained in detail here http://docs.oracle.com/javase/specs/jls ... l#jls-15.7

[anathema]

On the explanation:

Evaluation Respects Parentheses and Precedence

aside from using mathematical operation like:

Code: Select all

int i = 3;
        int j =  3 * (9 + 3);
        System.out.println(j); //results to 36

are there any other examples that this rule apply? I tried using

Code: Select all

  int i = 0;
        int z = 0;
        if(i++ < 5 || (++z <0 && 5 > z++) || 6 < ++i){
            System.out.println("Routed here");
        }
        System.out.println("i: " + i);
        System.out.println("z: " + z);

but it results to i: 1 and z:0. It seems that the evaluation on that if example is still from left to right.

[admin]

Well, what do you think 5 + 9/3; would print if the rules of precedence were not followed?

[sir_Anduin@yahoo.de]

This is explained in detail here http://docs.oracle.com/javase/specs/jls ... l#jls-15.7

could you point me to the right spot? After reading for a while, I was not able to find the explanation.

Thanks

[admin]

Well, the explanation is not about this question but about evaluation order. You need to read the whole chapter on evaluation order to understand the rules of evaluation in Java.
In short, in case of iA[0] = i = 30, to assign a value to iA[0], you have to evaluate the right hand side first, which is i = 30. So 30 will be assigned to i first.

HTH,
Paul.

[sir_Anduin@yahoo.de]

thanks, that was enough explanation for me

[uvsmtid]

JSL is not concise in this case and requires jumping across sections to consolidate confusing details.

Trivially: array access operator [] takes precedence in expression (it is even higher than ()).
Complication: array access operator [] has two parts: (1) left-hand outer part to reference array, (2) inner part to reference index within array. And the 1st part is evaluated first. That's it - see Example 15.10.4-1. Array Reference Is Evaluated First.

It could have been much easier explained if array access operator [] was included in official Operator Precedence.
NOTE:

• This link is to "Oracle Java Tutorial" (not even JSL) - it seems there is no section with such table in JSL!!!
• There is even no mentioning of operator () in this link to explicitly change precedence (just like the absence of array access [] operator).

So, if these operators were listed in operator precedence table like in this unofficial Java material,
the explanation would be trivial: follow operator precedence!!!

[karlose2006]

Me tome la molestia de replicar el ejercicio y el resultado efectivamente es la asignacion del valor 30 en la poscision 0

public class TestClass{    
public static void main(String args[] ){       
int i = 0 ;       
int[] iA = {10, 20} ;       
iA = i = 30 ;       
System.out.println(""+ iA[ 0 ] + " " + iA[ 1 ] + "  "+i) ;     
}
}

Can anyone explain why iA = i = 30 doesn't get processed as follows?
iA[0] = i = 30 ----> iA[0] = 0 = 30
If the left side operand gets evaluated first, the iA[0] should be assigned i which was initially set 0 before i = 30 gets evaluated, correct?

[futurecap]

I think, this information is useful here:

"...assignment operators are evaluated right to left."

https://docs.oracle.com/javase/tutorial ... ators.html

[dameest]

I think, this information is useful here:

"...assignment operators are evaluated right to left."

https://docs.oracle.com/javase/tutorial ... ators.html

This is what lead me to the wrong answer for this question, because regarding array indexing, which is part of the left of the assignement, it's evaluated before the right operand (the contrary of the quoted statement). So the java documentation is confusing about it, if you don't read the full spec.