optimize code

src/main/java/com/faf223/expensetrackerfaf/controller/ExpenseController.java

@@ -15,8 +15,12 @@ import java.util.List;
 @RequestMapping("/expenses")
 public class ExpenseController {
 
+    private final ExpenseService expenseService;
+
     @Autowired
-    private ExpenseService expenseService;
+    public ExpenseController(ExpenseService expenseService) {
+        this.expenseService = expenseService;
+    }
 
     @GetMapping("/user/{userUuid}")
     public ResponseEntity<List<Expense>> getExpensesByUser(@PathVariable String userUuid) {

src/main/java/com/faf223/expensetrackerfaf/controller/IncomeController.java

@@ -14,8 +14,13 @@ import java.util.List;
 @RestController
 @RequestMapping("/incomes")
 public class IncomeController {
+
+    private final IncomeService incomeService;
+
     @Autowired
-    private IncomeService incomeService;
+    public IncomeController(IncomeService incomeService) {
+        this.incomeService = incomeService;
+    }
 
     @GetMapping("/user/{userUuid}")
     public ResponseEntity<List<Income>> getIncomesByUser(@PathVariable String userUuid) {

src/main/java/com/faf223/expensetrackerfaf/controller/UserController.java

@@ -13,8 +13,12 @@ import org.springframework.web.bind.annotation.RestController;
 @RequestMapping("/users")
 public class UserController {
 
+    private final UserService userService;
+
     @Autowired
-    private UserService userService;
+    public UserController(UserService userService) {
+        this.userService = userService;
+    }
 
     @GetMapping("/{userUuid}")
     public ResponseEntity<User> getUser(@PathVariable String userUuid) {