写一个简单自定义异常

写一个简单自定义异常

首先创建实例User类

public class User {
          
   
	String name;
	int age;
	
	public User() {
          
   
		
	}
	public User(String name,int age) {
          
   
		this.name=name;
		this.age=age;
	}
	@Override
	public String toString() {
          
   
		return  name + ":" + age ;
	}
	
}

自定义一个异常类UserException继承Exception

public class UserException extends Exception {
          
   

	private static final long serialVersionUID = 1L;

	public UserException() {
          
   
		super();
		// TODO Auto-generated constructor stub
	}

	public UserException(String message, Throwable cause, boolean enableSuppression, boolean writableStackTrace) {
          
   
		super(message, cause, enableSuppression, writableStackTrace);
		// TODO Auto-generated constructor stub
	}

	public UserException(String message, Throwable cause) {
          
   
		super(message, cause);
		// TODO Auto-generated constructor stub
	}

	public UserException(String message) {
          
   
		super(message);
		// TODO Auto-generated constructor stub
	}

	public UserException(Throwable cause) {
          
   
		super(cause);
		// TODO Auto-generated constructor stub
	}

	
}

编写异常消息

public class UserDao {
          
   
	public void saveUser(User user) throws UserException{
          
   
		//假设已存在name=a age=20的数据
		if(user.toString().equals("a:20")) {
          
   
			throw new UserException("已存在");
		}
		System.out.println("储存成功");
	}
}

写一个测试类

public class UserService extends UserException{
          
   
	private static final long serialVersionUID = 1L;
	UserDao ud = new UserDao();
	public static void main(String[] args) throws UserException {
          
   
		//这里写一个已经存在的数据让程序抛异常
		User user = new User("a",20);
		UserService s = new UserService();
		s.updateUser(user);
		
	}
	public void updateUser(User user) throws UserException {
          
   
		 ud.saveUser(user);
			
	}
}

结果：