Operators

[Thomas Misik]

I am fairly confident in most uses of all operators used in Java, but there are some that still cause a bit of confusion. They would be:
^ (XOR) on Binary or boolean;
? - for instance: (as seen in MindQ)
Q).If arr[] contains only positive integer values, what does this function do?
public int guessWhat( int arr[] )
{ int x= 0;
for( int i = 0; i < arr.length; i++ )
x = x < arr[i] ? arr[i] : x;
return x;
}
/* Will this return the highest positive integer value in this array? */
If anyone knows a good (and concise) source on these operators and there functions, could they please post a link up? It would be greatly appreciated.
Thanks,
Thomas

[Stephanie Grasson]

Thomas,
(1) ^ (XOR) on binary or boolean
The XOR operation says that the operands MUST be different.
In other words,
1 XOR 0 produces 1 and
0 XOR 1 produces 1 but
1 XOR 1 produces 0 and
0 XOR 0 produces 0.
Here are the tables to use:
(bitwise XOR table)
Op1 ----- Op2 ----- Op1 XOR Op2
0 ----- 0 ----- 0
0 ----- 1 ----- 1
1 ----- 0 ----- 1
1 ----- 1 ----- 0
(boolean XOR table)
Op1 ----- Op2 ----- Op1 XOR Op2
false ----- false ----- false
false ----- true ----- true
true ----- false ----- true
true ----- true ----- false
(2) ?: (conditional operator)
The conditional operator is just a convenient way to code simple conditions (if/else) into a single statement.
The variable on the left side of the ? must be a boolean.
It is evaluated first.
If the result of this evaluation is true, the result of the entire expression is the value of the sub-expression to the left of the colon. If the result is false, the result of the entire expression is the value of the sub-expression to the right of the colon.
For example:

int a = 1;
int b = 2;
int c = 3;
boolean x = true;
a = x ? b : c

What does a equal?
x is true, so a = b;
If x was false, a = c;
a = x ? b : c is the same as

if(x)
{
    a = b;
}
else
{
    a = c;
}

You are right about the MindQ question, guessWhat() will return the highest positive integer value in the array.
Hope this helps. If not, let me know.
Stephanie

[Jane Griscti]

Hi Thomas,
Your code does return the highest value in the array. I tested it with the following:

class TestTernary {
public int guessWhat( int arr[] )
{ int x= 0;
    for( int i = 0; i < arr.length; i++ )
        x = x < arr[i] ? arr[i] : x;
    return x;
}
public static void main(String[] args) {
    int[] array = {7, 5, 3,9, 1, 2,10, 4, 6, 8};
    TestTernary t = new TestTernary();
    System.out.println(t.guessWhat(array));    
}
}

and the value '10' was returned.
The ternary or conditional operator (?:) is a short form 'if' construct. It takes the following form:

   boolean expression ? operand1 : operand2 

Basically,

if the boolean expression evaluates to 'true'
    return operand1
else
    return operand2.

Hope that helps.
------------------
Jane

[Thomas Misik]

Stephanie & Jane,
Thanks a lot guys, it was much appreciated. All of the Java I have written has been using Ultraedit; I've written many if statements, but have not really had to worry about ?: . It seems a rather silly question now, but I definitely needed some clarification on it. Thanks again, and since I'm writing the exam at the end of this month, I'm sure I'll be asking some more questions soon
Thomas