打印出数组列表中的所有对象

Question

可能重复:
如何以正确的方式打印对象内容？

我需要能够在我的数组列表中打印出Student对象(所有变量).这可能吗？当我尝试打印时输出这种东西,例如student.Student@82701e.我认为这是hexadecimal什么的

这是我的代码:

package student;

public class Student {

    private String studentName;
    private String studentNo;
    private String email;
    private int year;


    public Student() {
        this.studentName = null;
        this.studentNo = null;
        this.email = null;
        this.year = -1;
    }

    public Student(String nName, String nNum, String nEmail, int nYr) {
        this.studentName = nName;
        this.studentNo = nNum;
        this.email = nEmail;
        this.year = nYr;
    }

    public void setStudentName(String newStudentName) {
        this.studentName = newStudentName;
    }

    public void setStudentNo(String newStudentNo) {
        this.studentNo = newStudentNo;
    }

    public void setEmail(String newEmail) {
        this.email = newEmail;
    }

    public void setYear(int newYear) {
        this.year = newYear;
    }

    public String getStudentName() {
        return studentName;
    }

    public String getStudentNo() {
        return studentNo;
    }

    public String getEmail() {
        return email;
    }

    public int getYear() {
        return year;
    }
}

package student;

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

public class studentTest {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);



        List<Student> Students = new ArrayList();


        Student student1 = new Student();

        student1.setStudentName("Bob Marley");
        student1.setStudentNo("N0002");
        student1.setEmail("student2@student.com");
        student1.setYear(2);

        Students.add(student1);

        Student student2 = new Student();

        student2.setStudentName("Bill Harvey");
        student2.setStudentNo("N0003");
        student2.setEmail("student3@student.com");
        student2.setYear(2);

        Students.add(student2);

        Student student3 = new Student();

        student3.setStudentName("John Beans");
        student3.setStudentNo("N0004");
        student3.setEmail("student4@student.com");
        student3.setYear(2);

        Students.add(student3);


        System.out.println("Add new students: ");
        System.out.println("Enter number of students to add: ");
        int countStudents = input.nextInt();

        for (int i = 0; i < countStudents; i++) {
            Student newStudents = new Student();


            System.out.println("Enter details for student: " + (i + 1));

            System.out.println("Enter name: ");
            newStudents.setStudentName(input.next());

            System.out.println("Enter Number: ");
            newStudents.setStudentNo(input.next());System.out.println("Search by student number: ");



            System.out.println("Enter email: ");
            newStudents.setEmail(input.next());

            System.out.println("Enter year: ");
            newStudents.setYear(input.nextInt());
            Students.add(newStudents);
        }


    }
}

Answer 1

每当您打印类的任何实例时,都会调用类的default toString实现Object,它将返回您正在获取的表示形式.它包含两部分: - Type和Hashcode

所以,在student.Student@82701e,你得到输出 - >

• student.Student是Type,和
• 82701e 是个 HashCode

因此,您需要覆盖类中的toString方法Student以获取所需String representation:

@Override
public String toString() {
    return "Student No: " + this.getStudentNo() + 
           ", Student Name: " + this.getStudentName();
}

所以,当你从main类中打印出来时ArrayList,它会toString为每个实例调用方法,overrided而不是Object类中的方法: -

List<Student> students = new ArrayList();

// You can directly print your ArrayList
System.out.println(students); 

// Or, iterate through it to print each instance
for(Student student: students) {
    System.out.println(student);  // Will invoke overrided `toString()` method
}

在上述两种情况下,将调用类中toString重写的方法,Student并打印每个实例的适当表示.

Answer 2

类中的覆盖toString()方法Student如下:

   @Override
   public String toString() {
        return ("StudentName:"+this.getStudentName()+
                    " Student No: "+ this.getStudentNo() +
                    " Email: "+ this.getEmail() +
                    " Year : " + this.getYear());
   }