got square, square root, exponent

src/main/java/rocks/zipcode/calcskin/CalcEngine.java

     public double multiply(double v, double v1) { return (v*v1);}
 
     public double divide(double v, double v1) { return (v/v1);}
-}
+
+        public double invert(double v) {
+            return (v*-1); }
+
+        public double exponent(double v, double v1){
+        return (Math.pow(v,v1)); }
+
+
+
+
+    }

src/main/java/rocks/zipcode/calcskin/CalcSkin.java

         launch(args);
     }
     private static final String[][] template = {
-            { "7", "8", "9", "/" },
-            { "4", "5", "6", "*" },
-            { "1", "2", "3", "-" },
-            { "0", "c", "=", "+" }
+            { "7", "8", "9", "/" , "x^2"},
+            { "4", "5", "6", "*" , "sqrt"},
+            { "1", "2", "3", "-" , "1/x"},
+            { "0", "c", "=", "+" , "x^y"}
     };
 
     private final Map<String, Button> accelerators = new HashMap<>();
     private DoubleProperty currentValue = new SimpleDoubleProperty();
     private CalcEngine calcEngine = new CalcEngine();
 
-    private enum Op { NOOP, ADD, SUBTRACT, MULTIPLY, DIVIDE }
+    private enum Op { NOOP, ADD, SUBTRACT, MULTIPLY, DIVIDE, SQUARED, SQUAREROOT, INVERT, EXPONENT  }
 
     private Op curOp   = Op.NOOP;
     private Op stackOp = Op.NOOP;
                 makeClearButton(button);
             } else if ("=".equals(s)) {
                 makeEqualsButton(button);
+            } else if ("x^2".equals(s)){
+                makeSquareButton(button);
+            } else if ("sqrt".equals(s)){
+                makeSquareRootButton(button);
+            } else if ("i/x".equals(s)){
+                makeInvertButton(button);
             }
         }
 
             case "-": triggerOp.set(Op.SUBTRACT); break;
             case "*": triggerOp.set(Op.MULTIPLY); break;
             case "/": triggerOp.set(Op.DIVIDE);   break;
-        }
+            case "x^y": triggerOp.set(Op.EXPONENT); break;
+}
         return triggerOp;
     }
 
         });
     }
 
+    private void makeSquareButton(Button button) {
+        button.setStyle("-fx-base: #48ff2f;");
+        button.setOnAction(new EventHandler<ActionEvent>() {
+            @Override
+            public void handle(ActionEvent actionEvent) {
+                currentValue.set(Math.pow(currentValue.get(), 2));
+            }
+        });
+    }
+
+    private void makeSquareRootButton(Button button) {
+        button.setStyle("-fx-base: #48ff2f;");
+        button.setOnAction(new EventHandler<ActionEvent>() {
+            @Override
+            public void handle(ActionEvent actionEvent) {
+                currentValue.set(Math.sqrt(currentValue.get()));
+            }
+        });
+    }
+
+    private void makeInvertButton(Button button) {
+        button.setStyle("-fx-base: #48ff2f;");
+        button.setOnAction(new EventHandler<ActionEvent>() {
+            @Override
+            public void handle(ActionEvent actionEvent) {
+                currentValue.set(1/currentValue.get());
+            }
+        });
+    }
+
     private void makeClearButton(Button button) {
         button.setStyle("-fx-base: mistyrose;");
         button.setOnAction(new EventHandler<ActionEvent>() {
         button.setOnAction(new EventHandler<ActionEvent>() {
             @Override
             public void handle(ActionEvent actionEvent) {
+
                 switch (stackOp) {
                     case ADD:      currentValue.set(calcEngine.add(previousValue.get(), currentValue.get())); break;
                     case SUBTRACT: currentValue.set(calcEngine.subtract(previousValue.get(), currentValue.get())); break;
                     case MULTIPLY: currentValue.set(calcEngine.multiply(previousValue.get(), currentValue.get())); break;
                     case DIVIDE:   currentValue.set(calcEngine.divide(previousValue.get(), currentValue.get())); break;
+                    case EXPONENT: currentValue.set(calcEngine.exponent(previousValue.get(), currentValue.get())); break;
+
                 }
             }
         });