java - 询问非基元数组列表

Question

我已经创建了ArrayList。我如何使用此列表从类中获取方法或属性。我尝试过，但无法找到任何解决方案。

我尝试进入数组列表中的元素并获取一些属性，但我不能。

    public static void printOptions() {
    System.out.println("Welcome to our university!");
    System.out.println("Operations:");
    System.out.println("1- College");System.out.println("a) Number of Departments");System.out.println("b) Number of Courses");System.out.println("c) Number of Professors");System.out.println("d) Number of Students");System.out.println("e) Report");
    System.out.println("2- Department");System.out.println("a) New");System.out.println("b) Number of Courses");System.out.println("c) Number of Students");System.out.println("d) Is Full");System.out.println("e) Enroll");System.out.println("f) Report");
    System.out.println("3- Course");System.out.println("a) New");System.out.println("b) Number of Students");System.out.println("c) Assign");System.out.println("d) Is assigned");System.out.println("e) Professor Name");System.out.println("f) Is Full");System.out.println("g) Enroll");System.out.println("h) Report");
    System.out.println("4- Professor");System.out.println("a) New");System.out.println("b) Display Salary");System.out.println("c) Get Raise");System.out.println("d) Report");
    System.out.println("5- Student");System.out.println("a) New");System.out.println("b) Report");
    System.out.println("6- Quit");
}

/**
 * @param args the command line arguments
 */
public static void main(String[] args) {
    // TODO code application logic here

    printOptions() ;
      List<Department> departmentList;departmentList = new ArrayList<>();
      List<Course> courseList ;courseList = new ArrayList<>();
      List<Professor> proffList = new ArrayList<>() ;
      List<Student> studentList;studentList = new ArrayList<>() ;



      Scanner in = new Scanner(System.in) ; 
    int d = 0 , c = 0  , p = 0 , s=0 ; 
    College AinShams = new College() ; 
    while (true){

        String option = in.nextLine() ; 
        if(!"6".equals(option)) {
            if ("2a".equals(option)) { // Define new department
                System.out.println("Department Name:");
                String depName = in.nextLine() ; 
                System.out.println("Department Description:");
                String depDescripe = in.nextLine() ;
                System.out.println("Department Max Students:");
                int max_num = in.nextInt() ;
                in.nextLine() ; 
                Department Department_Name = new Department(depName, depDescripe, max_num); 

               //  departmentList.add(Department_Name);
                 departmentList.add(d, Department_Name);
                d++ ;
                AinShams.setDepart(departmentList);

            }

            else if ("4a".equalsIgnoreCase(option)) {//new proff
                System.out.println("Professor Firstname:");
                String firstName = in.nextLine() ;
                System.out.println("Professor Lastname:");
                String lastName = in.nextLine(); 
                System.out.println("Professor telephone:");
                String telephone = in.nextLine();
                System.out.println("Professor address:");
                String address = in.nextLine();
                System.out.println("Professor salary:");
                double salary = in.nextDouble() ;
                Professor proff = new Professor(firstName, lastName, telephone, address, salary); 
                proffList.add(p,proff) ;
                p++ ; 
                AinShams.setProf(proffList);
               }

            else if ("2e".equalsIgnoreCase(option)) {//add student in department
                System.out.println("Department:");
                String dep= in.nextLine() ;
                System.out.println("Student:");
                String stu= in.nextLine();   

              //  System.out.println(AinShams.getDepart());
              AinShams.getDepart().
                /*for (int i = 0; i < AinShams.getDepart().size(); i++) {
        }*/
            }
            System.out.println("============");
            System.out.println("Enter Operation");
            System.out.println("============");
        }else {break ;}


    }

}

}

在条件(2e)中，我需要获取我在数组List中分配的类中的方法和属性

Answer 1

AinShams.getDepart() 引用您定义为数据类型 College 的对象:

College AinShams = new College(); 

学院代码的其余部分不在该片段中，因此我无法判断 .getDepart() 方法是否存在。不管怎样，College 都不是一个 ArrayList。

如果你想访问 ArrayList 中对象的方法和字段，类似下面的内容就可以了。作为示例，我采用名为 Departmentlist 的 ArrayList，并使用 get() 方法返回该列表中的第 0 个元素。假设该类的第 0 个元素是 Department 类型的对象，.name 要求提供 name 字段(再次假设该 name 变量存在于 Department 类中)。 .getName() 是获取名称值的更好方法，但需要您在 Department 类中编写此方法。

departmentlist.get(0).name
departmentlist.get(0).getName()

顺便说一句，请考虑使用“\n”换行键格式化输出，以减少代码顶部的一些“System.out.println()”困惑。尝试使用 1 个 system.out.println 调用来打印两行文本，这两个示例:

System.out.println("Welcome to our university!" + "\n" + "Operations:");
System.out.println("Welcome to our university! \nOperations:");