java - 类数组列表的迭代器

Question

我是 Java 新手，所以如果我的问题看起来很愚蠢，请多多包涵。

我正在学习集合，我编写了一个程序来存储学生姓名 id 和标记。我将所有这些存储在 Arraylist 中。使用 for 循环我可以在我的程序中打印值。但是我不知道如何使用迭代器来做到这一点。我的代码是这样的。

学生.Java

public class Student{
   private String name;
   private String rollno;
   private String biology;
   private String maths;
   private String science;

   public Student(String name,String rollno,String biology,String maths,String science){
      setName(name);
      setRollno(rollno);
      setBiology(biology);
      setMaths(maths);
      setScience(science);
   }       

   public void setRollno(String rollno){
      this.rollno=rollno;
   }

   public String getRollno(){
      return rollno;
   }

   public void setName(String name){
      this.name=name;
   }

   public String getName(){
      return name;
   }

   public void setBiology(String biology){
      this.biology=biology;
   }

   public String getBiology(){
      return biology;
   }

   public void setMaths(String maths){
      this.maths=maths;
   }

   public String getMaths(){
      return maths;
   }

   public void setScience(String science){
      this.science=science;
   }

   public String getScience(){
      return science;
   }


}

College.Java 是我的主要类(class)

import java.util.*;

public class College{

public static void main(String args[]){

    ArrayList<Student> details = new ArrayList<Student>();
    Student Jb=new Student("Jb   ","417","92","97","90");
    Student Laxman=new Student("Lucky","418","93","97","96");
    Student Ajay=new Student("AJ   ","419","89","95","93");
    Student Venky=new Student("Venky","420","96","90","91");
    Student Satti=new Student("Satti","421","70","94","96");

    details.add(Jb);

    details.add(Laxman);
    details.add(Ajay);
    details.add(Venky);
    details.add(Satti);

    for(int i=0;i<details.size();i++)
    {
        Student student=details.get(i);

        System.out.println("Student Name : "+student.getName()+" Roll Number : "+student.getRollno()+" Biology : "+student.getBiology()+" Maths : "+student.getMaths()+" Science : "+student.getScience());

    }
  }    
}

在这种情况下，我得到了正确的输出。

如果我删除 for 循环并用迭代器替换。我收到一些错误消息，提示 Object cannot be converted as Student

这是我的代码

ListIterator itr=details.listIterator();
while(itr.hasNext())
{
   //Object student=itr.next();
   Student student=itr.next();
   System.out.println("Student Name : "+student.getName()+" Roll Number : "+student.getRollno()+" Biology : "+student.getBiology()+" Maths : "+student.getMaths()+" Science : "+student.getScience());
}

请指导我这里有什么问题以及如何更正。

Answer 1

正如你所拥有的，你必须显式地转换它:

 Student student=(Student)itr.next();

或更改您的 ListIterator 以使用泛型

ListIterator<Student> itr=details.listIterator();

但另一个更容易阅读的替代方法是 foreach 循环

for (Student student : details) {
     System.out.println("Student Name : "+student.getName()+" Roll Number : "+student.getRollno()+" Biology : "+student.getBiology()+" Maths : "+student.getMaths()+" Science : "+student.getScience());
}