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return statement

Posted on 2014-10-29
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Hi,

I am going through below challenge solution

http://codingbat.com/prob/p140449

I have not understood below return statement.

  return (talking && (hour < 7 || hour > 20));

Please advise.
public boolean parrotTrouble(boolean talking, int hour) {
  return (talking && (hour < 7 || hour > 20));
  // Need extra parenthesis around the || clause
  // since && binds more tightly than ||
  // && is like arithmetic *, || is like arithmetic +
}
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Question by:gudii9
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by:
ozo earned 668 total points
ID: 40411054
http://docs.oracle.com/javase/tutorial/java/nutsandbolts/op2.html
&& is  Conditional-AND;  false when left operand (talking) is false, otherwise evaluate the second operand
|| is Conditional-OR;  true when the left operand (hour < 7) is true, otherwise evaluate the second operand (hour > 20)

Without the parentheses, talking && hour < 7 || hour > 20 would evaluate as ((talking && hour < 7) || hour > 20)
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Assisted Solution

by:Kimputer
Kimputer earned 664 total points
ID: 40411072
While I don't understand the coding logic (why it returns, for what reason), interpreting the code is simple.

 parrotTrouble(True, 1) = True
 parrotTrouble(True, 8) = False
 parrotTrouble(True, 21) = True
 parrotTrouble(False, 1) = False
 parrotTrouble(False, 8) = False
 parrotTrouble(False, 21) = False

It just returns the AND of the two variables. Talking is either True or False, it's already input as the first variable.
The second part is evaluated from the second variable. If hours is below 7 OR above 20, that second part is True (otherwise False).
With these two outcomes, you do the AND operation again for the final result.
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Assisted Solution

by:krakatoa
krakatoa earned 668 total points
ID: 40411307
>>talking && (hour < 7 || hour > 20)

Quite simply - talking has to be true, and hour has to be EITHER less than 7 OR more than 20, then a final true is returned - otherwise false is returned of course.
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Expert Comment

by:krakatoa
ID: 40411389
Thanks.

Footnote : (now you've done the challenge) -

This would be a way of splitting the logic up also :

public boolean parrotTrouble(boolean talking, int hour) {

   if (talking==false) {return talking;}
  return (hour<7||hour>20);
  
}

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Expert Comment

by:ozo
ID: 40411410
//If you're going to split it up
 if( !talking ){ return false; }
  if( hour<7 ){ return true; }
  return hour>20;
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Expert Comment

by:krakatoa
ID: 40411421
You can do that too of course, but I was sticking to the illustration of keeping the ORs together.
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Expert Comment

by:krakatoa
ID: 40411427
And don't forget our old friend Mr Ternary

return talking = talking==true?hour<7||hour>20?true:false:false;

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Expert Comment

by:krakatoa
ID: 40411445
This might also be an option at some point :

if ((!(talking==false))&& !((hour>6)&&(hour<21))){return true;}
           else{return false;}

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- which is just for people who don't like ors. ;)

OR should it be :

if ((!(talking==false))&& !((hour>6)&&(hour<21))){return !false;}
           else{return !true;}

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Expert Comment

by:ozo
ID: 40411496
Presumably those are just meant to be silly, but
 !((hour>6)&&(hour<21))
is not equivalent to
 (hour < 7 || hour > 20)
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Expert Comment

by:krakatoa
ID: 40411519
They are not silly inasmuch as they all pass the codingbat tests - so maybe the tests are silly.
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by:krakatoa
ID: 40411540
Remember that >6 and <21 are the hours that ARE ok to speak.

(and so for the record, your ID: 40411496 is not correct).

You can look at it this way :
"<x OR >y" MUST be the complement of ">=x AND <=y".
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by:ozo
ID: 40413299
Sorry, I misread "!((>x-1)&&(<y+1))", expecting  ">=x AND <=y" (one of the reasons to avoid silly extraneous transforms)
!((hour>6)&&(hour<21)) is equivalent when hour is an int
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Expert Comment

by:krakatoa
ID: 40413339
Right, ok.
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