How to use this boolean in an if statement?

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.

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.

The problem here is

if (stop = true) is an assignation not a comparision.

Try if (stop == true)

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

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();
}