some changes

Calculator.java

@@ -6,7 +6,6 @@ public class Calculator
     // instance variables - replace the example below with your own
     private double displayValue;
     private double memoryValue;
-    private boolean err;
 
     /**
      * Constructor for objects of class Calculator
@@ -15,7 +14,6 @@ public class Calculator
     {
         displayValue = 0;
         memoryValue = 0;
-        err = false;
     }