我知道这是一个困惑的实现，但我基本上有这段代码(我编写了所有代码)，并且我需要能够在使用适当的菜单选项时从列表中删除学生或讲师。代码中的其他所有内容均有效，只是菜单选项 3 和 4 无效。我在尝试删除时为对象输入了完全相同的信息。这是代码。所有三个类都在下面。

驱动类:

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

public class Driver {
private ArrayList<Student> students;
private ArrayList<Instructor> instructors;

public static void main(String[] args) {        
    Driver aDriver = new Driver();
    aDriver.run();      
}

public Driver() {
    students = new ArrayList<Student>();
    instructors = new ArrayList<Instructor>();
}

private void run() {
    Student aStudent;
    Instructor anInstructor;
    Scanner inp = new Scanner(System.in);
    int choice = -1;
    String str = "Enter a menu option:\n";

    str += " 0: Quit\n";
    str += " 1: Add new student\n";
    str += " 2: Add new instructor\n";
    str += " 3: Delete existing student\n";
    str += " 4: Delete existing instructor\n";
    str += " 5: Print list of students\n";
    str += " 6: Print list of instructors\n";
    str += "Your choice: ";

    do {
        System.out.print(str);
        choice = inp.nextInt();

        switch(choice) {
        case 0:
            System.out.println("Thanks! Have a great day!");
            break;
        case 1:
            aStudent = getStudentInfo();
            addStudent(aStudent);
            break;
        case 2:
            anInstructor = getInstructorInfo();
            addInstructor(anInstructor);
            break;
        case 3:
            aStudent = getStudentInfo();
            deleteStudent(aStudent);
            break;
        case 4:
            anInstructor = getInstructorInfo();
            deleteInstructor(anInstructor);
            break;
        case 5:
            printStudents();
            break;
        case 6:
            printInstructors();
            break;
        default:
            System.out.println("Invalid menu item " + choice);  
        }
    }
    while(choice != 0);
}

public Student getStudentInfo() {
    Student aStudent;
    String name = null;
    String id = null;
    double GPA = 0.0;
    Scanner inp = new Scanner(System.in);

    System.out.print("\n\nEnter the student's name: ");
    name = inp.nextLine();
    System.out.print("Enter the student's ID: ");
    id = inp.nextLine();
    System.out.print("Enter the student's GPA: ");
    GPA = inp.nextDouble();

    aStudent = new Student(name, id, GPA);
    return aStudent;
}

public Instructor getInstructorInfo() {
    Instructor anInstructor;
    String name = null;
    String id = null;
    String dept = null;
    String email = null;
    Scanner inp = new Scanner(System.in);

    System.out.print("\n\nEnter the instructor's name: ");
    name = inp.nextLine();
    System.out.print("Enter the instructor's ID: ");
    id = inp.nextLine();
    System.out.print("Enter the instructor's department: ");
    dept = inp.nextLine();
    System.out.print("Enter the instructor's email address: ");
    email = inp.nextLine();

    anInstructor = new Instructor(name, id, dept, email);
    return anInstructor;
}

public void addStudent(Student aStudent) {
    students.add(aStudent);
}

public void addInstructor(Instructor anInstructor) {
    instructors.add(anInstructor);
}

public void deleteStudent(Student aStudent) {
    students.remove(aStudent);
}

public void deleteInstructor(Instructor anInstructor) {
    instructors.remove(anInstructor);
}

public void printStudents() {
    System.out.println("\n\n" + Student.printHeader());

    for(int i = 0; i < students.size(); i++) {
        System.out.print(students.get(i));
    }

    System.out.print("\n\n");
}

public void printInstructors() {
    System.out.print("\n\n" + Instructor.printHeader());

    for(int i = 0; i < instructors.size(); i++) {
        System.out.print(instructors.get(i));
    }

    System.out.print("\n\n");
}
}

学生类(class):

public class Student {
private String name;
private String id;   //String to allow for the possibility of leading zeroes
private double GPA;

public Student() {
    name = "TestFirst TestLast";
    id = "00000";
    GPA = -1.00;
}

public Student(String name1, String id1, double GPA1) {
    name = name1;
    id = id1;
    GPA = GPA1;
}

public static String printHeader() {
    String str = String.format("%-25s%-7s%-6s\n", "Name", "ID", "GPA");
    return str;
}

public String toString() {
    String str = String.format("%-25s%-7s%-6.3f\n", name, id, GPA);
    return str;
}

public String getName() {
    return name;
}

public void setGPA(double GPA2) {
    GPA = GPA2;
}
}

导师类(class):

public class Instructor {
private String name;
private String id;
private String dept;
private String email;

public Instructor() {
    name = "TestFirst TestLast";
    id = "-00001";
    dept = "TestDept";
    email = "test@test.net";
}

public Instructor(String name1, String id1, String dept1, String email1) {
    name = name1;
    id = id1;
    dept = dept1;
    email = email1;
}

public static String printHeader() {
    String str = String.format("%-30s%-6s%-15s%-15s\n", "Name", "ID", "Department", "Email Address");
    return str;
}

public String toString() {
    String str = String.format("%-30s%-6s%-15s%-15s\n", name, id, dept, email);
    return str;
}

public String getName() {
    return name;
}
}

最佳答案

您必须为 Student 和 Instructor 类正确覆盖 equals() 方法。

当覆盖 equals 时，最好也覆盖 hashCode()。 新学生(姓名、身份证、GPA)；

例如，像这样:

public boolean equals(Object o) {
  if (!(o instanceof Student)) {
    return false;
  }
  Student other = (Student) o;
  return name.equals(other.name) && id.equals(other.id) && GPA == other.GPA;
}

public int hashCode() {
  return name.hashCode();
}

这样，您就有机会让 ArrayList 找出哪个对象对应于您在删除时作为参数传递的对象。如果您不覆盖上述方法，它将使用 Object 中的默认实现，当您删除一个新的 Student 对象时，它会比较明显不同的内存地址。

您可以在 Object 的 javadoc 中阅读有关这 2 个方法的更多信息。

关于java - ArrayList.remove() 没有删除对象，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/12697407/