For Each Loop Inside a If Statement?

Try

if( letter == null || letter.equals(" ") ||  checkArray(array, letter))
{
    ...
}


boolean checkArray(String[] arryay, String letter)
{
     for(String a: array) 
           if(letter.equals(a)) 
                return true;

     return false;
}

Note: checking letter for null after you have already called equals() does not make too much sense; i've reordered those.

You cannot. Perhaps you should move the if statement into the for statement?

As rfausak said, a for statement does not return a boolean. You should have made that an answer by the way.

If you use a Set you could write:

if ( (letter.equals(" ")) || (letter == null) || (a.contains(letter)) ) {}

Well, that´s because you can not have a for loop within an if condition. It seems you want to see if the letter is within the array array; if so then you can do it with Apache commons-lang's ArrayUtils:

ArrayUtils.contains( array, letter );

This wont work because a for doesn't evaluate to a boolean. For readabilities sake you should extract that to a method anyway, good examples appear in other answers.

Other points, you should rejig your conditionals to not be susceptible to NullPointerExceptions

if (letter == null || " ".equals(letter) || arrayContains(array, letter)) {
        //...
}

If you are able to add additional libraries, there are some nice apache commons libraries to make this work easier, namely StringUtils in commons-lang and CollectionUtils in commons-collections.

You also may like to harden that input checking if it's possible to get Strings larger than one character, by using String#trim() after checking for null. Again, this would be a good candidate for an extracted method isBlank(String str).