Author homepage : Designer Xiao Zheng
Author brief introduction : 3 years of JAVA full-stack development experience, focusing on JAVA technology, system customization, remote guidance, dedicated to enterprise digital transformation, certified lecturer of CSDN College and Blue Bridge Cloud Course.
Main direction : Vue, SpringBoot, WeChat applet
This article explains the concept of custom exceptions in Java, demonstrates the usage of custom exceptions, and gives sample codes. Custom exceptions refer to exception classes created by users according to their own needs.
Table of contents
1. What is a custom exception
In Java, custom exceptions refer to exception classes created by users according to their own needs. Java provides some predefined exception classes, such as NullPointerException, ArrayIndexOutOfBoundsExceptionetc., but sometimes these predefined exception classes cannot fully meet our needs. In such cases, we can represent specific exceptional conditions by creating custom exception classes.
Custom exception classes usually inherit from Exceptionclasses or RuntimeExceptionclasses, and their subclasses, and add corresponding constructors and other methods as needed to meet specific exception handling requirements. Custom exception classes can contain additional attributes and methods to provide More information and features.
When using a custom exception class, the usual practice is to use throwa statement in the method to throw a custom exception, and then use a try-catchstatement block to catch and handle the exception at the place where the method is called.
The advantage of a custom exception class is that it makes the code more readable and maintainable. By using a custom exception class, we can better describe and handle specific exception situations and provide more detailed error information.
2. How to define custom exceptions
When defining a custom exception, you first need to create a class and inherit from the exception class provided by Java, such as Exceptionor RuntimeException, and then add custom constructors and other methods. The following is a simple sample code that shows how to define a custom exception Define the exception class, please study carefully.
public class MyCustomException extends Exception {
public MyCustomException(String message) {
super(message);
}
// 可以添加其他构造方法和额外的方法
}
In the above example, MyCustomExceptionthe class inherits from Exceptionthe class and adds a constructor with a string parameter. Through this custom exception class, we can throw, catch and handle specific exception conditions.
When using a custom exception class, the usual practice is to use throwthe statement in the method to throw the custom exception, and then use the try-catchstatement block to catch and handle the exception where the method is called. The following is a sample code that demonstrates how to use the self-defined exception class. Define the exception class, please study carefully.
public class MyClass {
public void performOperation(int value) throws MyCustomException {
if (value < 0) {
throw new MyCustomException("Value cannot be negative");
}
// 其他操作逻辑
}
public static void main(String[] args) {
MyClass myObject = new MyClass();
try {
myObject.performOperation(-1);
} catch (MyCustomException e) {
System.out.println("Caught custom exception: " + e.getMessage());
}
}
}
In the above example, performOperationthe method checks if the input value is negative and if so, throws a custom exception MyCustomException. In the method, we catch and handle this custom exception mainby using the statement block, and then output the exception information.try-catch
By customizing exception classes, we can better describe and handle specific exception situations, and provide more detailed error information. Using custom exception classes also makes the code more readable and maintainable.
3. Application scenarios of custom exceptions
Custom exceptions have many application scenarios in Java, the following are 5 55 common application scenarios, please study carefully.
- Business logic exceptions : During the development process, you may encounter situations where certain business rules need to throw exceptions. For example, when the data entered by the user does not conform to specific business rules, a custom exception can be thrown to indicate this situation, so as to better handle and prompt the user.
- Data verification exception : In the process of data verification, sometimes an exception needs to be thrown to indicate that the data is illegal or does not meet the requirements. For example, when the length of the password entered by the user is less than the specified minimum length, a custom exception can be thrown to remind the user that the password is too short.
- File operation exceptions : When performing file operations, such as reading, writing, or deleting files, exceptions such as file non-existence and insufficient permissions may occur. You can customize exceptions to represent these specific file operation exceptions and handle them accordingly.
- Abnormal network operation : During network communication, such as sending
HTTPrequests, processingSocketconnections and other operations, abnormal situations such as network connection timeout and connection disconnection may occur. Custom exceptions can be used to catch and handle these network operation exceptions. - Concurrent operation exception : In a multi-threaded or concurrent programming environment, problems such as thread safety and race conditions may be encountered. You can define custom exceptions to represent abnormal conditions related to these concurrent operations and handle them accordingly.
The application scenarios of custom exceptions vary according to project requirements. Through custom exceptions, specific exception situations can be better described and handled, more detailed error information can be provided, and the code can be more readable and maintainable. When using custom exceptions When abnormal, it needs to be designed and used reasonably according to the actual situation, so as to avoid abuse and confusion of the concept of exception.
4. Custom abnormal interview questions
1. What is a custom exception? Why use custom exceptions?
Answer: Custom exception refers to the exception class created according to your own needs. In Java, although there are many predefined exception classes, sometimes these exception classes cannot fully meet our needs, so we need to create custom exception classes. Custom exception classes can better describe and handle specific exception situations, provide more detailed error information, and make code more readable and maintainable.
2. How to define a custom exception class?
Answer: To define a custom exception class, you need to create a class and inherit from the exception classes provided by Java, such as , Exception, RuntimeExceptionand then add custom constructors and other methods to meet specific exception handling requirements.
3. How to use custom exceptions?
Answer: When using a custom exception, the usual practice is to use the statement in the method to throwthrow the custom exception, and then use try-catchthe statement block where the method is called to catch and handle the exception.
4. What properties and methods can custom exception classes have?
Answer: Custom exception classes can add various attributes and methods according to requirements. Generally speaking, custom exception classes add constructors to receive exception information, and can also add other methods to provide additional functionality.
5. What is the difference between custom exceptions and predefined exceptions?
Answer: Custom exceptions are exception classes created according to your own needs, while predefined exceptions are some defined exception classes provided by Java. Custom exceptions can better describe and handle specific exceptions and provide more detailed error information, while predefined exceptions are usually some general exception classes.
V. Summary
This article explains the concept of custom exceptions in Java, demonstrates the usage of custom exceptions, and gives sample codes. In the next blog, I will explain how to use the File class to read and write files.
