在Java编程中，如何在学生ID重复时停止后续代码执行？

import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class StudentManager {

    private static Map<String, Student> studentMap = new HashMap<>();

    public static int addStudent() {
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入学生ID：");
        String studentId = scanner.next();

        if (studentMap.containsKey(studentId)) {
            System.out.println("学生ID已存在，添加失败！");
            return 0; // ID重复，立即返回
        }

        Student student = new Student();
        student.setId(studentId);
        System.out.print("请输入学生姓名：");
        student.setName(scanner.next());
        System.out.print("请输入学生年龄：");
        student.setAge(scanner.nextInt());
        System.out.print("请输入学生住址：");
        student.setAddress(scanner.next());

        studentMap.put(studentId, student);
        System.out.println("学生信息添加成功！");
        return 1;
    }


    public static class Student {
        private String id;
        private String name;
        private int age;
        private String address;

        //getter and setter methods
        public String getId() { return id; }
        public void setId(String id) { this.id = id; }
        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 String getAddress() { return address; }
        public void setAddress(String address) { this.address = address; }
    }

    public static void main(String[] args) {
        addStudent();
    }
}