Using methods and constructors to construct a basic calculator
This can be simplified:

double exp(double op1, double op2){
double result = 1;
while (op2 &gt; 0){
    result = result * op1;
    op2--;
}

return result;
}


You should be using the Math.pow() method:

double exp(double op1, double op2){
    return Math.pow(op1, op2);
}


Also, you should use proper indentation to help you read and understand your code better, which will help prevent bugs.

This doesn't do anything:

simpleCalc(){

}


It is best to remove code like this to make your project easier to understand and maintain.