帮我写一个java的增删改查

### 回答1：
当涉及到增删改查的操作时，通常会使用Java的CRUD（Create, Read, Update, Delete）操作。以下是Java中实现CRUD操作的示例代码。

假设我们要创建一个简单的学生类，其中包括学生的姓名、年龄和成绩。我们将在以下示例代码中使用这个类。

public class Student {
    private String name;
    private int age;
    private double score;

    public Student(String name, int age, double score) {
        this.name = name;
        this.age = age;
        this.score = score;
    }

    // getter and setter methods
    public String getName() {
        return name;
    }

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

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public double getScore() {
        return score;
    }

    public void setScore(double score) {
        this.score = score;
    }
}

接下来，我们将使用一个名为`StudentDao`的类来执行CRUD操作。该类包含以下方法：

public interface StudentDao {

    // 添加一个学生
    public void addStudent(Student student);

    // 根据学生姓名查询学生
    public Student getStudent(String name);

    // 更新学生信息
    public void updateStudent(Student student);

    // 删除学生
    public void deleteStudent(Student student);

}

现在我们将实现`StudentDao`接口的具体实现，这里我们将使用`ArrayList`来存储学生列表。

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

public class StudentDaoImpl implements StudentDao {

    private List<Student> students;

    public StudentDaoImpl() {
        students = new ArrayList<Student>();
    }

    // 添加一个学生
    public void addStudent(Student student) {
        students.add(student);
    }

    // 根据学生姓名查询学生
    public Student getStudent(String name) {
        for (Student student : students) {
            if (student.getName().equals(name)) {
                return student;
            }
        }
        return null;
    }

    // 更新学生信息
    public void updateStudent(Student student) {
        for (Student s : students) {
            if (s.getName().equals(student.getName())) {
                s.setAge(student.getAge());
                s.setScore(student.getScore());
                return;
            }
        }
    }

    // 删除学生
    public void deleteStudent(Student student) {
        students.remove(student);
    }
}

现在我们已经完成了一个简单的Java增删改查的示例代码。

### 回答2：
当然可以帮您写一个Java的增删改查示例代码。以下是一个简单的学生管理系统的例子，用于演示增删改查操作：

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

public class StudentManagementSystem {
    
    private List<Student> students;
    
    public StudentManagementSystem() {
        students = new ArrayList<>();
    }
    
    public void addStudent(Student student) {
        students.add(student);
        System.out.println("学生添加成功！");
    }
    
    public void deleteStudent(int studentId) {
        boolean found = false;
        for (Student student : students) {
            if (student.getStudentId() == studentId) {
                students.remove(student);
                System.out.println("学生删除成功！");
                found = true;
                break;
            }
        }
        if (!found) {
            System.out.println("学生不存在！");
        }
    }
    
    public void updateStudent(int studentId, String newName) {
        boolean found = false;
        for (Student student : students) {
            if (student.getStudentId() == studentId) {
                student.setName(newName);
                System.out.println("学生信息更新成功！");
                found = true;
                break;
            }
        }
        if (!found) {
            System.out.println("学生不存在！");
        }
    }
    
    public Student getStudent(int studentId) {
        for (Student student : students) {
            if (student.getStudentId() == studentId) {
                return student;
            }
        }
        return null;
    }
    
    public void displayAllStudents() {
        System.out.println("所有学生信息：");
        for (Student student : students) {
            System.out.println("学生ID：" + student.getStudentId() + "，姓名：" + student.getName());
        }
    }
    
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        StudentManagementSystem sms = new StudentManagementSystem();
        
        while (true) {
            System.out.println("请选择操作：1-添加学生，2-删除学生，3-修改学生信息，4-查询学生信息，5-显示所有学生信息，0-退出");
            int choice = scanner.nextInt();
            
            if (choice == 0) {
                break;
            }
            
            switch (choice) {
                case 1:
                    System.out.println("请输入学生ID：");
                    int studentId = scanner.nextInt();
                    System.out.println("请输入学生姓名：");
                    String name = scanner.next();
                    sms.addStudent(new Student(studentId, name));
                    break;
                case 2:
                    System.out.println("请输入要删除的学生ID：");
                    int deleteId = scanner.nextInt();
                    sms.deleteStudent(deleteId);
                    break;
                case 3:
                    System.out.println("请输入要修改的学生ID：");
                    int updateId = scanner.nextInt();
                    System.out.println("请输入新的学生姓名：");
                    String newName = scanner.next();
                    sms.updateStudent(updateId, newName);
                    break;
                case 4:
                    System.out.println("请输入要查询的学生ID：");
                    int queryId = scanner.nextInt();
                    Student student = sms.getStudent(queryId);
                    if (student != null) {
                        System.out.println("学生ID：" + student.getStudentId() + "，学生姓名：" + student.getName());
                    } else {
                        System.out.println("学生不存在！");
                    }
                    break;
                case 5:
                    sms.displayAllStudents();
                    break;
                default:
                    System.out.println("无效的操作！");
                    break;
            }
        }
        
        scanner.close();
    }
}

class Student {
    private int studentId;
    private String name;
    
    public Student(int studentId, String name) {
        this.studentId = studentId;
        this.name = name;
    }
    
    public int getStudentId() {
        return studentId;
    }
    
    public String getName() {
        return name;
    }
    
    public void setName(String name) {
        this.name = name;
    }
}

这个示例代码实现了一个学生管理系统，您可以通过输入选择添加学生、删除学生、修改学生信息、查询学生信息和显示所有学生信息等操作。希望这个示例能帮助到您！