Java开发预约中心程序时循环内赋值变量无法外部调用问题求助

• 局部变量未初始化：Java方法内的局部变量没有默认初始值，你声明的name和time仅在用户选择「1. 预约」的分支才会被赋值，若用户未创建预约直接触发查询操作，变量处于未初始化状态，触发编译报错。
• 逻辑缺陷：查询分支的do-while循环条件appointment<appointment+1永远为真，会触发死循环；现有逻辑仅支持存储单条预约，多次提交预约会覆盖之前的记录；Scanner在循环内重复创建，且nextInt()读取后残留的换行符会导致后续nextLine()读取到空值。

仅需支持存储一条预约的场景，可通过初始化变量、修复查询逻辑解决报错：

import java.util.Scanner; 
public class appointment {
    public static void main(String[]args) {
        int input;
        int appointment = 0;
        // 给变量赋初始值解决未初始化报错
        String name = null;
        int time = 0;
        // Scanner移到循环外，避免重复创建
        Scanner sc = new Scanner(System.in);
        do { 
            System.out.println("Welcome to ACEPrep Appointment Center! How can we help you? \n(1. Make an appointment 2. Check Appointment Details 3. Check Number of Appointments 4. Leave)");
            input=Integer.parseInt(sc.nextLine());
            if(input==1) {
                System.out.println("Name:");
                name=sc.nextLine();
                System.out.println("Select a time between 1-8 PM:");
                time=sc.nextInt();
                // 读取nextInt残留的换行符，避免下次循环nextLine读空
                sc.nextLine();
                System.out.println("Saved! You have an appointment at " + time +" PM with " + name);
                appointment++;
            }
            if(input==2) {
                // 先判断是否有预约，避免输出空值
                if(appointment == 0) {
                    System.out.println("You have no appointments yet.");
                } else {
                    System.out.println("You have an appointment with " + name + " at " + time + " PM"); 
                }
            }
            if(input==3) {
                System.out.println("You have " + appointment + " appointment(s).");
            }
            if(input==4) {
                System.out.println("Thank you for using us! Goodbye!");
                break;
            }
        }while(input<4);
        sc.close();
    }
}

如果需要支持存储多条预约，可通过集合存储每条预约记录：

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

// 预约实体类，存储每条预约的姓名和时间
class AppointmentItem {
    String name;
    int time;
    public AppointmentItem(String name, int time) {
        this.name = name;
        this.time = time;
    }
}

public class appointment {
    public static void main(String[]args) {
        int input;
        // 用ArrayList存储所有预约
        ArrayList<AppointmentItem> appointmentList = new ArrayList<>();
        Scanner sc = new Scanner(System.in);
        do { 
            System.out.println("Welcome to ACEPrep Appointment Center! How can we help you? \n(1. Make an appointment 2. Check Appointment Details 3. Check Number of Appointments 4. Leave)");
            input=Integer.parseInt(sc.nextLine());
            if(input==1) {
                System.out.println("Name:");
                String name=sc.nextLine();
                System.out.println("Select a time between 1-8 PM:");
                int time=sc.nextInt();
                sc.nextLine();
                appointmentList.add(new AppointmentItem(name, time));
                System.out.println("Saved! You have an appointment at " + time +" PM with " + name);
            }
            if(input==2) {
                if(appointmentList.isEmpty()) {
                    System.out.println("You have no appointments yet.");
                } else {
                    System.out.println("Your appointments:");
                    for(int i=0; i<appointmentList.size(); i++) {
                        AppointmentItem item = appointmentList.get(i);
                        System.out.println((i+1) + ". Appointment with " + item.name + " at " + item.time + " PM");
                    }
                }
            }
            if(input==3) {
                System.out.println("You have " + appointmentList.size() + " appointment(s).");
            }
            if(input==4) {
                System.out.println("Thank you for using us! Goodbye!");
                break;
            }
        }while(input<4);
        sc.close();
    }
}

内容的提问来源于stack exchange，提问作者di on Minecraft