How to use this boolean in an if statement?

Question

private String getWhoozitYs(){
    StringBuffer sb = new StringBuffer();
    boolean stop = generator.nextBoolean();
    if(stop = true)
    {
        sb.append("y");
        getWhoozitYs();
    }
    return sb.toString();
}

This is a chunk of code for a project I'm doing in a programming course. The problem I'm having is that after declaring the boolean stop and trying to assign a randomly generated boolean value to it, I can't use it in the if statement to determine if I should append more y's to the StringBuffer or not. I do have the Random generator inside a constructor, so that part isn't a problem. I assumed that since I declared the boolean outside the if statement I would be able to use it inside, but that doesn't seem to be the case. The real question is how can I use a randomly determined boolean in an if statement.

Hey i think you may figure this one out, it's a nice puzzle.. look up casting. esp. 0 and 1 — Caffeinated, Mar 14 '13 at 15:04
Also, you can simply say `if(stop)` See this - http://stackoverflow.com/questions/3793650/convert-boolean-to-int-in-java — Caffeinated, Mar 14 '13 at 15:05

Maroun · Answer 1 · 2016-04-14T11:52:06.433

27

if(stop = true) should be if(stop == true), or simply (better!) if(stop).

This is actually a good opportunity to see a reason to why always use if(something) if you want to see if it's true instead of writing if(something == true) (bad style!).

By doing stop = true then you are assigning true to stop and not comparing.

So why the code below the if statement executed?

See the JLS - 15.26. Assignment Operators:

At run time, the result of the assignment expression is the value of the variable after the assignment has occurred. The result of an assignment expression is not itself a variable.

So because you wrote stop = true, then you're satisfying the if condition.

edited Apr 14 '16 at 11:52

answered Mar 14 '13 at 15:03

Maroun

94,125
30
188
241

4

Actually, it should just be `if (stop)`. That's not even open to misinterpretation due to typos. :P – cHao Mar 14 '13 at 15:04
1

the if is still comparing, it's just since stop gets set to true, it will always evaluate to true. sorry this is a nitpick but it seems like something worth explaining (since the OP is a beginner). – Nathan Hughes Mar 14 '13 at 15:07
One doubt... `if(stop)` and `if(stop == true)` does second one need extra cpu cycles for execution. Programatically both interprete same, then why is it bad to use? – kAmol Jan 10 '17 at 08:35
1

@unknown No complexity difference between the two. It's just like asking "Is it true that the variable is true" instead of "Is the variable true". – Maroun Jan 10 '17 at 08:36
@MarounMaroun yes but at cpu instruction level I doubt that is the case. Because "is it true that the variable is true" has 2 conditions I think. Do you have any document or something for it? – kAmol Jan 11 '17 at 06:58
And `if(stop)` can also be written as `if(((stop==true)==true)==true)` ? I mean won't it affect? I'm not asking for code complexity, but for cpu cyle execution level. Just for why is it bad style? – kAmol Jan 11 '17 at 07:01
@unknown I think that most compilers will optimize this. – Maroun Jan 11 '17 at 11:24
for me `if(stop)` doesnt seem to work. However, if I do `if(stop == true)`, it works. Any thoughts? – Obaid Maroof Mar 30 '17 at 17:04
@obaidmaroof no way.. please check again. – Maroun Mar 30 '17 at 18:50

score 5 · Answer 2 · edited Aug 07 '23 at 07:20

5

The problem here is

if (stop = true) is an assignment not a comparison.

Try if (stop == true)

Also take a look at the Top Ten Errors Java Programmers Make.

edited Aug 07 '23 at 07:20

mirekphd

4,799
3
38
59

answered Mar 14 '13 at 15:04

Averroes

4,168
6
50
63

Vincent van der Weele · Answer 3 · 2013-03-15T08:17:19.573

3

Actually, the entire approach would be cleaner if you only had to use one instance of StringBuffer, instead of creating one in every recursive call... I would go for:

private String getWhoozitYs(){
     StringBuffer sb = new StringBuffer();
     while (generator.nextBoolean()) {
         sb.append("y");
     }

     return sb.toString();
}

edited Mar 15 '13 at 08:17

answered Mar 14 '13 at 15:15

Vincent van der Weele

12,927
1
33
61

Achintya Jha · Answer 4 · 2013-03-14T15:12:06.827

2

if(stop == true)

or

if(stop)

= is for assignment.

== is for checking condition.

if(stop = true)

It will assign true to stop and evaluates if(true). So it will always execute the code inside if because stop will always being assigned with true.

edited Mar 14 '13 at 15:12

answered Mar 14 '13 at 15:04

Achintya Jha

12,735
2
27
39

score 1 · Answer 5 · answered Mar 14 '13 at 15:04

1

Since stop is boolean you can change that part to:

//...
if(stop) // Or to: if (stop == true)
{
   sb.append("y");
   getWhoozitYs();
}
return sb.toString();
//...

answered Mar 14 '13 at 15:04

CloudyMarble

36,908
70
97
130

score 1 · Answer 6 · answered Mar 14 '13 at 15:05

1

Try this:-

private String getWhoozitYs(){
    StringBuffer sb = new StringBuffer();
    boolean stop = generator.nextBoolean();
    if(stop)
    {
        sb.append("y");
        getWhoozitYs();
    }
    return sb.toString();
}

answered Mar 14 '13 at 15:05

Rahul Tripathi

168,305
31
280
331

score 1 · Answer 7 · answered Mar 14 '13 at 15:05

1

= is for assignment

write

if(stop){
   //your code
}

or

if(stop == true){
   //your code
}

answered Mar 14 '13 at 15:05

mp5

159
1
11

score 1 · Answer 8 · answered Mar 14 '13 at 15:06

1

additionally you can just write

if(stop)
{
        sb.append("y");
        getWhoozitYs();
}

answered Mar 14 '13 at 15:06

MondayPaper

1,569
1
15
20

How to use this boolean in an if statement?

8 Answers8

Linked

Related