如何迭代，搜索和显示ArrayList中的特定元素

Question

我对程序的特定部分有疑问。 我想做的是迭代，搜索和显示ArrayList中的元素。

因此，我尝试对代码的主要功能实现自己的代码段以进行尝试：

else if (menuChoice==3) {
           System.out.println("Search Student:");
           String search = input.nextLine();

           for (Student student : students)
           {
               if (students.equals(search)){
                   System.out.println(student);
               }
           }
       }

希望它可以遍历ArrayList并访问/显示列表中的特定元素。 它返回空白，我在做什么错？

如果您想知道，这是完整的代码：

package student;
import java.util.*;

public class Student
{
private String r_name;
private int r_age;
private String r_course;
private String r_year;
private String r_section;
private String r_studno;

public Student( String name, int age, String course, String year, String section, String studno )
{
    r_name = name;
    r_age = age;
    r_course = course;
    r_year = year;
    r_section = section;
    r_studno = studno;
}

public String getName()
{
    return r_name;
}

public int getAge()
{
    return r_age;
}

public String getCourse()
{
    return r_course;
}

public String getYear()
{
    return r_year;
}

public String getSection()
{
    return r_section;
}

public String getStudno()
{
    return r_studno;
}

public String toString()
{
    return "Name: " + r_name + ", Age: " + r_age + 
           ", Course: " + r_course + ", Year: " + r_year +
           ", Section: " + r_section + ", Student Number: " + r_studno;
}

public static void main(String[] args) 
{
   ArrayList<Student> students = new ArrayList<Student>();
   Scanner input = new Scanner(System.in);

   int menuChoice = 4;
   do {
       System.out.println("\t\t\tStudent Record Menu");
       System.out.println("\t\t1. Add Student\t2. View Students\t3. Search Student\t4. Exit");
       try {
           System.out.println("Enter a choice: ");
           menuChoice = Integer.parseInt(input.nextLine());
       } catch (NumberFormatException e) {
           continue;
       }

       if (menuChoice==1)
       {
           System.out.println("Add a Student");
           System.out.println("Full name:");
           String name = input.nextLine();

           int age = -1;
           do {
               try {
                   System.out.println("Age:");
                   age = Integer.parseInt(input.nextLine());
               } catch (NumberFormatException e) {
                   System.out.println("Enter a number!");
                   continue;
               }
           } while (age <= 0);

           System.out.println("Course:");
           String course = input.nextLine();

           System.out.println("Year:");
           String year = input.nextLine();

           System.out.println("Section:");
           String section = input.nextLine();

           System.out.println("Student Number:");
           String studno = input.next();

           Student student = new Student(name, age, course, year, section, studno);
           students.add(student);

       } else if (menuChoice==2) {
           System.out.println("Students:");
           for (Student student : students)
           {
               System.out.println(student);
           }
       } else if (menuChoice==3) {
           System.out.println("Search Student:");
           String search = input.nextLine();

           for (Student student : students)
           {
               if (students.equals(search)){
                   System.out.println(student);
               }
           }
       }

   } while (menuChoice<4);
}
}

Answer 1

您正在检查ArrayList students是否等于String search 。 结果只能是假的。 我想，您正在尝试执行以下操作：

for (Student student : students)
{
    if (student.getName().equals(search))
    {
        System.out.println(student);
        break;//assuming student name are unique. remove if not
    }
}

Answer 2

您必须将搜索键与学生的键ID进行比较，例如，如果所有名称都是唯一的，则使用

 for (Student student : students)
       {
           if (student.getname().equals(search)){
               System.out.println(student);
           }
       }

您正在使用搜索键对整个学生对象参考进行比较

如果您想显示全部内容，那么您将必须采用一种方法，使用id获得所有详细信息，例如：

getStudentbyname( String studentname){

here comes the code to get all data

}

然后在for循环中调用方法并存储在数组中

 for (Student student : students)
       {
           if (student.getname().equals(search)){
              Arraylist<String> studentarr = student.getStudentbyname(student.getname());

System.out.println(""+studentarr)
           }
       }