课设 简单的银行账户管理 求各位大神帮忙解答如何读取ID，判断用户是否存在

[qq_19667115]

主函数Main

import java.io.IOException;


public class Main {

	public static void main(String[] args) throws IOException, ClassNotFoundException {

		Choice K=new Choice();
		K.menu();
	}
} 

Choice类

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.*;


public class Choice {
		List<User> list=new ArrayList<User>();
		Scanner input=new Scanner(System.in);
			
		// 选择菜单		
		public void menu() throws IOException, ClassNotFoundException{
				System.out.println("请选择:1-管理员          2-用户          0-退出");
				int i=input.nextInt();
				//管理
					if(i==1){
						Admin();
				int x=input.nextInt();   //输入菜单号
					if(x==1){
						addAccount();     //开户
						}
					if(x==2){
						queryAccount();   //查询账户
						}
					if(x==0){
						returnMain();     //退出
						}
					}
				//用户
					if(i==2){
						User();
					}	
				//退出
					if(i==0){
						returnMain();
						}
				}

						
		//管理员模块				
		public void Admin(){	
			System.out.println("管理员模块菜单");
			System.out.println("1-开户");
			System.out.println("2-查询所有账户");
			System.out.println("0-退出");
			System.out.print("请输入菜单号:");
		}
		
		//开户模块
		public void addAccount() throws IOException, ClassNotFoundException{
		User a=new User();
		System.out.print("请输入开户户名:");
		a.setName(input.next());		
		System.out.print("请输入开户金额:");
		a.setMoney(input.nextDouble());	
		System.out.print("请选择利息类型(1.固定利率  2.浮动利率):");
		a.setType(input.nextInt());	
		a.setID(a.ID);
		list.add(a);	
		System.out.println("----------------------");
		System.out.println("	开户成功");
		System.out.println("----------------------");
		returnMain();
		}
		
		//查询模块
		public void queryAccount() throws IOException, ClassNotFoundException{
			for (User a : list) {
			System.out.println("帐户ID:"+a.ID+"\t"+"账户名:"+a.getName()+"\t"+"帐户余额:"+a.getMoney());			
			}
			returnMain();
		}
		
		//返回菜单
		public void returnMain() throws IOException, ClassNotFoundException{
			menu();
		}
		public void returnUser() throws IOException, ClassNotFoundException{
			User();
		}
		//用户模块	
		public void User() throws ClassNotFoundException, IOException {
			System.out.println("用户模块菜单");
			System.out.println("1-存款");
			System.out.println("2-取款");
			System.out.println("3-查看本账户利息");
			System.out.println("0-退出");
			System.out.println("请首先输入账户ID:");
			}

}

User类

import java.io.Serializable;


public class User implements Serializable {

	String name;
	double money;
	int type;
	int ID=0;
	static int bh=100;
	{
		ID=bh;
		bh++;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public double getMoney() {
		return money;
	}
	public void setMoney(double money) {
		this.money = money;
	}
	public int getType() {
		return type;
	}
	public void setType(int type) {
		this.type = type;
	}
	public int getID() {
		return ID;
	}
	public void setID(int ID) {
		this.ID = ID;
	}
	public User(String name,double money,int type,int ID) {
		super();
		this.name = name;
		this.money = money;
		this.type = type;
		this.ID = ID;
	}
	public User() {
			super();
		}
	public String toString() {
		return "账户ID:"+ID+"账户名:"+name+"存款金额:"+money+"利率类型:"+type;
	}


}

[computerclass]

首先你得有用户呀