I am getting this error, but it isn't very helpful in that it doesn't point me near where the error is happening. What do the numbers after the error mean? I have been looking at the error for the last few hours, but I don't really get where the error is coming from. My code is:

val str = "(and x y)";

def stringParse ( exp: String, expreshHolder: ArrayBuffer[String] ): ArrayBuffer[String] = { //takes three arguments, string, int, arraybuffer

    var b = 0; //position of where in the expression String I am currently in
    var temp = expreshHolder; //holder of expressions without parens
    if(temp == 0) b = 0; else {b = temp(temp.length-1).toInt; temp.remove(temp.length-1)} //this sets the position of wherever the string was read last plus removes that check from the end of the ArrayBuffer
    var arrayCounter = temp.length; //just counts to make sure an empty spot in the array is there to put in the strings

    if(exp(b) == '(') {
        b = b + 1;

        while(exp(b) == ' '){b = b + 1;} //point of this is to just skip any spaces between paren and start of expression type
        if(exp(b) == 'a') {
            //first create the 'and', 'or', 'not' expression types to figure out 
            temp += exp(b).toString; 
            b = b+1; 
            temp(arrayCounter) = temp(arrayCounter) + exp(b).toString; //concatenates the second letter
            b = b+1; 
            temp(arrayCounter) = temp(arrayCounter) + exp(b).toString; //concatenates the last letter for the expression type
            arrayCounter+=1
            //this part now takes the symbols and puts them in an array
            b+=1;
            while(exp(b) == ' ') {b+=1;} //just skips any spaces until it reaches the first symbol
            if(exp(b) == '(') { temp += b.toString; temp = stringParse(exp, temp);
            b = temp(temp.length-1).toInt; 
            temp.remove(temp.length-1); 
            arrayCounter = temp.length 
            } else {
            temp += exp(b).toString; 
            arrayCounter+=1; b+=1; }
            while(exp(b) == ' ') {b+=1;} //just skips any spaces until it reaches the second symbol

            if(exp(b) == '(') { temp += b.toString; temp = stringParse(exp, temp); 
                            b = temp(temp.length-1).toInt; 
                            temp.remove(temp.length-1); 
                            arrayCounter = temp.length } else {temp += exp(b).toString; arrayCounter+=1; b+=1; }    
        }
    temp;
    } else { 
      temp(arrayCounter) +="failed"; temp;} //this is just incase it fails and I should probably check this incase it fails when it doesnt encounter an opening paren
}//end of while loop

hold = stringParse(str, ho );
for(test <- hold) println(test);

Sorry for the amount of code, but from what I can tell it is correct. The point of this code is to read this the first string at the top and just put "and", "x", "y" in an array. Its suppose to do it on more complicated ones, but I am trying it on a simple version first to test and make sure it works. The error I am getting is:

java.lang.ArrayIndexOutOfBoundsException: -1
at scala.collection.mutable.ResizableArray$class.apply(ResizableArray.scala:45)
at scala.collection.mutable.ArrayBuffer.apply(ArrayBuffer.scala:44)
at Driver$.stringParse$1(Driver.scala:19)
at Driver$.main(Driver.scala:60)
at Driver.main(Driver.scala)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at scala.tools.nsc.util.ScalaClassLoader$$anonfun$run$1.apply(ScalaClassLoader.scala:78)
at scala.tools.nsc.util.ScalaClassLoader$class.asContext(ScalaClassLoader.scala:24)
at scala.tools.nsc.util.ScalaClassLoader$URLClassLoader.asContext(ScalaClassLoader.scala:88)
at scala.tools.nsc.util.ScalaClassLoader$class.run(ScalaClassLoader.scala:78)
at scala.tools.nsc.util.ScalaClassLoader$URLClassLoader.run(ScalaClassLoader.scala:101)
at scala.tools.nsc.ObjectRunner$.run(ObjectRunner.scala:33)
at scala.tools.nsc.ObjectRunner$.runAndCatch(ObjectRunner.scala:40)
at scala.tools.nsc.MainGenericRunner.runTarget$1(MainGenericRunner.scala:56)
at scala.tools.nsc.MainGenericRunner.process(MainGenericRunner.scala:80)
at scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:89)
at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)

any help on being able to read this error message and understand where it is happening? Thanks in advance.

• arrays
• scala

It means the variable you are decrementing has reached -1

Also note that all you need do is follow the line numbers. For example, the first place to look is line '45'

 scala.collection.mutable.ResizableArray$class.apply(ResizableArray.scala:45)

Tackle the methods you wrote first.

The error is on the 19th line of Driver.scala:

at Driver$.stringParse$1(Driver.scala:19)

Take a gander:

if(temp == 0) b = 0; else {b = temp(temp.length-1).toInt; temp.remove(temp.length-1)} 

temp is a ArrayBuffer[String], not a number, so temp == 0 will always be false. That means the else clause will always execute, even when temp.length is 0.