This class (or a class that this class inherits from) is marked as '@immutable', but one or more of its instance fields aren't fina
时间: 2024-03-27 10:35:44 浏览: 166
这个错误提示是因为你在一个被标记为 `@immutable` 的类中定义了一个非 `final` 的实例变量。在 Dart 中,被标记为 `@immutable` 的类是不可变的,它们的实例在创建后就不能再被修改。因此,这些类的实例变量必须被标记为 `final`,以确保它们在创建后不能被修改。
如果你想要在一个被标记为 `@immutable` 的类中定义一个可变的实例变量,那么你可以使用 `late` 关键字来延迟变量的初始化,例如:
```
@immutable
class Person {
late String name;
late int age;
Person({ required this.name, required this.age });
}
```
在上面的例子中,`name` 和 `age` 是可变的实例变量,但是它们被延迟初始化,直到第一次被使用时才会被赋值。这样就可以避免在创建对象时出现错误提示。
当然,最好的方法是遵循 `@immutable` 类的规则,将所有实例变量标记为 `final` 或使用 `late` 延迟初始化。这样可以确保代码的可读性和稳定性。
相关问题
使用java完成下列任务1. Read the sample code listing 5.1 to 5.3 of Core Java. 2. Implement a class of Person including fields of id, name, gender, age, and the methods to access these fields as well as a desciption function. 3. Implement a class of Student that inherits the Person class by adding additional fields of major and gpa. In addition, the methods include the accessors to get all the fields, respectively. 4. Rewrite the description function, and test it using three kinds of initializations.
Sure, I can help you with that. Here is the solution to your problem:
1. Sample code listing 5.1 to 5.3 of Core Java:
```
//listing 5.1
public class Manager extends Employee {
private double bonus;
public Manager(String name, double salary, int year, int month, int day) {
super(name, salary, year, month, day);
bonus = 0;
}
public double getSalary() {
double baseSalary = super.getSalary();
return baseSalary + bonus;
}
public void setBonus(double bonus) {
this.bonus = bonus;
}
}
//listing 5.2
public class Employee {
private String name;
private double salary;
private LocalDate hireDay;
public Employee(String name, double salary, int year, int month, int day) {
this.name = name;
this.salary = salary;
hireDay = LocalDate.of(year, month, day);
}
public String getName() {
return name;
}
public double getSalary() {
return salary;
}
public LocalDate getHireDay() {
return hireDay;
}
public void raiseSalary(double byPercent) {
double raise = salary * byPercent / 100;
salary += raise;
}
}
//listing 5.3
public class ManagerTest {
public static void main(String[] args) {
Manager boss = new Manager("Carl Cracker", 80000, 1987, 12, 15);
boss.setBonus(5000);
Employee[] staff = new Employee[3];
staff[0] = boss;
staff[1] = new Employee("Harry Hacker", 50000, 1989, 10, 1);
staff[2] = new Employee("Tommy Tester", 40000, 1990, 3, 15);
for (Employee e : staff) {
System.out.println("name=" + e.getName() + ",salary=" + e.getSalary());
}
}
}
```
2. Implementation of a class of Person including fields of id, name, gender, age, and the methods to access these fields as well as a description function:
```
public class Person {
private int id;
private String name;
private String gender;
private int age;
public Person(int id, String name, String gender, int age) {
this.id = id;
this.name = name;
this.gender = gender;
this.age = age;
}
public int getId() {
return id;
}
public String getName() {
return name;
}
public String getGender() {
return gender;
}
public int getAge() {
return age;
}
public String getDescription() {
return "ID: " + id + ", Name: " + name + ", Gender: " + gender + ", Age: " + age;
}
}
```
3. Implementation of a class of Student that inherits the Person class by adding additional fields of major and gpa. In addition, the methods include the accessors to get all the fields, respectively:
```
public class Student extends Person {
private String major;
private double gpa;
public Student(int id, String name, String gender, int age, String major, double gpa) {
super(id, name, gender, age);
this.major = major;
this.gpa = gpa;
}
public String getMajor() {
return major;
}
public double getGpa() {
return gpa;
}
public String getDescription() {
return super.getDescription() + ", Major: " + major + ", GPA: " + gpa;
}
}
```
4. Rewrite the description function, and test it using three kinds of initializations:
```
public static void main(String[] args) {
// initialization 1
Person person1 = new Person(1, "John", "Male", 30);
System.out.println(person1.getDescription());
// initialization 2
Person person2 = new Person(2, "Jane", "Female", 25);
System.out.println(person2.getDescription());
// initialization 3
Student student1 = new Student(3, "Mike", "Male", 20, "Computer Science", 3.8);
System.out.println(student1.getDescription());
}
```
Output:
```
ID: 1, Name: John, Gender: Male, Age: 30
ID: 2, Name: Jane, Gender: Female, Age: 25
ID: 3, Name: Mike, Gender: Male, Age: 20, Major: Computer Science, GPA: 3.8
```
I hope this solution helps you. Let me know if you have any questions or need further assistance.
here are two ways to use PythonLibCore, either by HybridCore or by using DynamicCore. HybridCore provides support for the hybrid library API and DynamicCore provides support for dynamic library API. Consult the Robot Framework User Guide, for choosing the correct API for library. Regardless which library API is chosen, both have similar requirements. Library must inherit either the HybridCore or DynamicCore. Library keywords must be decorated with Robot Framework @keyword decorator. Provide a list of class instances implementing keywords to library_components argument in the HybridCore or DynamicCore __init__. It is also possible implement keywords in the library main class, by marking method with @keyword as keywords. It is not requires pass main library instance in the library_components argument. All keyword, also keywords implemented in the classes outside of the main library are available in the library instance as methods. This automatically publish library keywords in as methods in the Python public API. The example in below demonstrates how the PythonLibCore can be used with a library.
The example code below demonstrates how to use PythonLibCore with a library:
```python
from robot.libraries.PythonLibCore import HybridCore, keyword
class MyLibrary(HybridCore):
def __init__(self):
super(MyLibrary, self).__init__(library_components=[self])
@keyword
def my_keyword(self, arg1, arg2):
return arg1 + arg2
```
In the above example, `MyLibrary` is a library class that inherits from `HybridCore`. The library class has a single keyword `my_keyword` decorated with the `@keyword` decorator.
The `__init__` method of `MyLibrary` calls the parent constructor and passes `self` as the only argument to the `library_components` parameter. This makes the `my_keyword` method available as a keyword in the library.
When the library is imported and instantiated, the `my_keyword` method can be called as a keyword from within a Robot Framework test case. For example:
```robotframework
*** Settings ***
Library MyLibrary
*** Test Cases ***
Example Test Case
${result}= My Keyword 1 2
Should Be Equal As Integers ${result} 3
```
In the above test case, the `My Keyword` keyword is used to call the `my_keyword` method of the `MyLibrary` instance. The result is then checked using the `Should Be Equal As Integers` keyword.
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