made some buttons

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

@@ -6,18 +6,35 @@ public class CalcEngine {
     }
 
     public double add(double v, double v1) {
-        return Double.NaN;
+        return v + v1;
     }
 
     public double subtract(double v, double v1) {
-        return Double.NaN;
+        return v - v1;
     }
 
     public double multiply(double v, double v1) {
-        return Double.NaN;
+        return v * v1;
     }
 
     public double divide(double v, double v1) {
-        return Double.NaN;
+        return v / v1;
+    }
+
+    public double squareRoot(double v1, double v) {
+        return Math.sqrt(v);
+    }
+
+    public double exponent(double v, double v1){
+        return Math.pow(v, v1);
+    }
+
+    public double invert(double v, double v1) {
+        return v * -1.0;
+    }
+
+    public double square(double v, double v1) {
+        return v * v;
     }
 }
+

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

@@ -18,16 +18,16 @@ import java.util.HashMap;
 import java.util.Map;
 
 // a simple JavaFX calculator.
-public class CalcSkin extends Application {
+public class CalcSkin extends Application{
 
     public static void main(String[] args){
         launch(args);
     }
     private static final String[][] template = {
-            { "7", "8", "9", "/" },
-            { "4", "5", "6", "*" },
-            { "1", "2", "3", "-" },
-            { "0", "c", "=", "+" }
+            { "7", "8", "9", "/", "S" },
+            { "4", "5", "6", "*", "SR" },
+            { "1", "2", "3", "-", "INV" },
+            { "0", "c", "=", "+", "EXP" }
     };
 
     private final Map<String, Button> accelerators = new HashMap<>();
@@ -36,7 +36,7 @@ public class CalcSkin extends Application {
     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, SQUARE, SQUARE_ROOT, EXPONENT, INVERT }
 
     private Op curOp   = Op.NOOP;
     private Op stackOp = Op.NOOP;
@@ -51,16 +51,16 @@ public class CalcSkin extends Application {
         final TilePane  buttons = createButtons();
 
         stage.setTitle("Calc");
-        stage.initStyle(StageStyle.UTILITY);
+        stage.initStyle(StageStyle.DECORATED);
         stage.setResizable(false);
         stage.setScene(new Scene(createLayout(screen, buttons)));
         stage.show();
     }
 
     private VBox createLayout(TextField screen, TilePane buttons) {
-        final VBox layout = new VBox(20);
+        final VBox layout = new VBox(70);
         layout.setAlignment(Pos.CENTER);
-        layout.setStyle("-fx-background-color: silver; -fx-padding: 20; -fx-font-size: 20;");
+        layout.setStyle("-fx-background-color: lightBlue; -fx-padding: 20; -fx-font-size: 20;");
         layout.getChildren().setAll(screen, buttons);
         handleAccelerators(layout);
         screen.prefWidthProperty().bind(buttons.widthProperty());
@@ -127,6 +127,10 @@ public class CalcSkin extends Application {
             case "-": triggerOp.set(Op.SUBTRACT); break;
             case "*": triggerOp.set(Op.MULTIPLY); break;
             case "/": triggerOp.set(Op.DIVIDE);   break;
+            case "S": triggerOp.set(Op.SQUARE);   break;
+            case "SR" : triggerOp.set(Op.SQUARE_ROOT); break;
+            case "EXP" : triggerOp.set(Op.EXPONENT); break;
+            case "INV" : triggerOp.set(Op.INVERT);  break;
         }
         return triggerOp;
     }
@@ -185,6 +189,10 @@ public class CalcSkin extends Application {
                     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 SQUARE:   currentValue.set(calcEngine.square(previousValue.get(), currentValue.get())); break;
+                    case SQUARE_ROOT: currentValue.set(calcEngine.squareRoot(previousValue.get(), currentValue.get())); break;
+                    case EXPONENT: currentValue.set(calcEngine.exponent(previousValue.get(), currentValue.get())); break;
+                    case INVERT:   currentValue.set(calcEngine.invert(previousValue.get(), currentValue.get())); break;
                 }
             }
         });