check if input was string

Valutakalkulator/src/Valutakalkulator/AppController.java

@@ -27,10 +27,15 @@ public class AppController {
     }
 
     private double getInput() {
-		if(input.getText().isEmpty())
+        String txt=input.getText();
+		if(txt.isEmpty())
 			return 0.0;
-
-		return Double.parseDouble(input.getText());
+        try {  
+            double nr = Double.parseDouble(txt); 
+            return nr;
+        } catch(NumberFormatException e){  
+            return 0.0;  
+        }  
 	}
 	
 	@FXML