【J2SE】——异常实践篇

         本文小编以用户登录为例，进行异常处理。

         首先新建实体类User.java：

/**
 * Created by why_768 on 2017/2/16.
 */
public class User {
    int id;
    String email;
    String pwd;
    public User(){

    }
    public User(int id,String email,String pwd){
        super();
        this.id=id;
        this.email=email;
        this.pwd=pwd;
    }
    @Override
    public String toString(){
        return id + "," + email;
    }
    @Override
    public boolean equals(Object obj){
        if(obj == null){
            return false;
        }
        if(this == obj){
            return true;
        }
        if(obj instanceof User){
            User o=(User)obj;
            return id == o.id;
        }
        return false;
    }
    @Override
    public int hashCode(){
        return id;
    }
}

          然后新建两种声明式异常：

/**
 * Created by why_768 on 2017/2/16.
 * 该类表示用户已经注册过异常
 */
public class UserExistsException extends Exception{
    public UserExistsException(String message){
        super(message);
    }
}

/**
 * Created by why_768 on 2017/2/16.
 * 该类表示用户或密码错误异常
 */
public class EmailOrPwdException extends Exception {
    public EmailOrPwdException(String message){
        super(message);
    }
}

         创建用户管理类UserManager：

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

/**
 * Created by why_768 on 2017/2/16.
 */
public class UserManager {
    //存储对象的集合，key是email，value是用户
    private Map<String,User> users=new HashMap<String, User>();
    private int id=1;
    public User reg(String email,String pwd) throws UserExistsException{
        if(users.containsKey(email)){
            throw new UserExistsException("该邮箱" + email + "已存在");
        }
        User user=new User(id++,email,pwd);
        users.put(email,user);
        return user;
    }
    public User login(String email,String pwd) throws EmailOrPwdException{
        if(!users.containsKey(email)){
            throw new EmailOrPwdException("无此用户！");
        }
        User user=users.get(email);
        if(!user.pwd.equals(pwd)){
            throw new EmailOrPwdException("密码错误！");
        }
        return user;
    }
}

          建立测试类：

public class Main {

    public static void main(String[] args) throws Exception{
        UserManager mgr=new UserManager();
        User user=mgr.reg("why_768@163.com","123");
        System.out.println("注册成功！");
       //测试1，重复注册，出现异常
        user=mgr.reg("why_768@163.com","123");
       //测试2，登录密码错误，出现异常，密码不对
        user=mgr.login("why_768@163.com","1233");
        //测试3，登录成功！
        User someone=mgr.login("why_768@163.com","123");
        System.out.println(someone);
    }
}

           总结：

 

         代码调用抛出异常的方法，必须处理异常，有两种方式：

        1、使用try catch finally 捕获

        2、直接再抛出异常

        处理异常的方式依赖具体业务逻辑，可灵活处理。