Validate budget setup, such that the entire budget amount must be used up before proceeding

src/main/java/no/ntnu/idatt1002/demo/controller/BudgetController.java

@@ -127,10 +127,24 @@ public class BudgetController extends FinanceController {
             ioe.printStackTrace();
             showErrorDialogBox(ioe.getMessage(), ioe.getMessage(), ioe.getMessage());
         }
+
+        double maxAmount = general.getMaxAmount();
         //Set calendar, disposable amount and amount left
         formatDatePicker();
-        disposableAmount.setText(String.valueOf(general.getMaxAmount()));
-        amountLeft.setText(String.valueOf(general.getMaxAmount()));
+        disposableAmount.setText(String.valueOf(maxAmount));
+        amountLeft.setText(String.valueOf(maxAmount));
+
+        //Prevent proceeding until all of budget has been used up
+        continueBtn.addEventFilter(
+            ActionEvent.ACTION, event -> {
+                if (maxAmount - general.totalSum() != 0) {
+                    event.consume();
+                    showErrorDialogBox("Use up budget",
+                        "Please distribute the entire disposable amount",
+                        "The amount must be used up before proceeding");
+                }
+            }
+        );
     }
 
     /**