java - 如何迭代并获取动态传递的类的值

Question

我有一个接受任何类类型对象的方法，我想迭代该对象并打印详细信息。

void showDetails(List<?> obj) {
    System.out.println(obj);
     for(Object ob : obj) {
        //how to print the course and student details
    } 
}

我如何迭代并打印传递的 obj 值的详细信息。下面是完整的示例代码。

import java.util.ArrayList;
import java.util.List;

class Student{
    private int stid;
    public int getStid() {
        return stid;
    }

    public void setStid(int stid) {
        this.stid = stid;
    }

}
class Details extends Student{
    private String name;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    private String address;
    public String getAddress() {
        return address;
    }
    public void setAddress(String address) {
        this.address = address;
    }


}

class Course extends Student{
    private String shortTerm;
    private String fullTerm;
    public String getShortTerm() {
        return shortTerm;
    }
    public void setShortTerm(String shortTerm) {
        this.shortTerm = shortTerm;
    }
    public String getFullTerm() {
        return fullTerm;
    }
    public void setFullTerm(String fullTerm) {
        this.fullTerm = fullTerm;
    }

}
public class Test {

    void showDetails(List<?> obj) {
        System.out.println(obj);
         for(Object ob : obj) {
            //how to print the course and student details
        } 
    }
    public static void main(String[] args) {

        Details d1 = new Details();
        d1.setName("John");
        d1.setAddress("Street 21");
        d1.setStid(10);
        Details d2 = new Details();
        d2.setName("Sam");
        d2.setAddress("Street 151");
        d2.setStid(11);
        List<Details> listObj = new ArrayList<>();
        listObj.add(d1);
        listObj.add(d2);

        new Test().showDetails(listObj);

        //course
        Course c1 = new Course();
        c1.setShortTerm("6months");
        c1.setFullTerm("12 months");
        c1.setStid(111);
        List<Course> courseList = new ArrayList<>();
        courseList.add(c1);
        new Test().showDetails(courseList);
    }
}

我想做showDetails(List<?> obj)作为通用方法，以便可以传递作为 Student 类的子类的任何类对象。 List<?> ，其中?表示作为 Student 类的子类的任何类对象。

Answer 1

执行此操作的标准多态方法是让 Student(及其子类)知道如何将其自己的详细信息转换为 String。例如，你可以有这样的东西:

class Student{
    private int stid;

    public int getStid() {
        return stid;
    }

    public void setStid(int stid) {
        this.stid = stid;
    }

    public String getDetails() {
        return "ID: " + getStid();
    }

}

class Details extends Student {

    /*
     ... other fields etc...
     */

    @Override
    public String getDetails() {
        StringBuilder sb = new StringBuilder();
        sb.append(super.getDetails()).append('\n');
        sb.append("Name: ").append(getName()).append('\n');
        // TODO: append other fields
        return sb.toString();
    }

}

class Course extends Student {

    /*
     ... other fields etc...
     */

    @Override
    public String getDetails() {
        StringBuilder sb = new StringBuilder();
        // TODO: similar to Details class
        return sb.toString();
    }
}

然后您的显示详细信息函数可以使用 getDetails() 方法:

void showDetails(List<? extends Student> obj) {
    System.out.println(obj);
     for(Student s : obj) {
        System.out.println(s.getDetails());
    } 
}