exceptions.md

Java Exceptions

Introduction

某类异常代表什么?

Categories

分类

• Error 系统异常 : 不应捕获
• Exception : 可以捕获
• Throwable : 包含 Error 和 Exception, 因此不应捕获它
• RuntimeException : 非受查异常

Unchecked Exception

非受查异常

• Unchecked Exceptions - The Controversy - Oracle Docs : https://docs.oracle.com/javase/tutorial/essential/exceptions/runtime.html
• Checked and Unchecked Exceptions in Java - Baeldung.com : https://www.baeldung.com/java-checked-unchecked-exceptions#when

"If it's so good to document a method's API, including the exceptions it can throw, why not specify runtime exceptions too?"

• Runtime exceptions represent problems that are the result of a programming problem, and as such, the API client code cannot reasonably be expected to recover from them or to handle them in any way.
• Such problems include arithmetic exceptions, such as dividing by zero; pointer exceptions, such as trying to access an object through a null reference; and indexing exceptions, such as attempting to access an array element through an index that is too large or too small.

Here's the bottom line guideline :

• If a client can reasonably be expected to recover from an exception, make it a checked exception.
• If a client cannot do anything to recover from the exception, make it an unchecked exception.

• Are checked exceptions good or bad? : https://www.infoworld.com/article/3142626/are-checked-exceptions-good-or-bad.html

• Checked exceptions are not really exceptions.
  • The thing about checked exceptions is that they are not really exceptions by the usual understanding of the concept.
  • Instead, they are API alternative return values.

Class Hierarchy

什么时候该用哪个异常类?

• Java 异常类继承层次 ( 类父子关系 )

References

• The Java Exception Class Hierarchy : https://airbrake.io/blog/java-exception-handling/the-java-exception-class-hierarchy

Throwable

Differ Throwable and Exception

• References
  • 9 Best Practices to Handle Exceptions in Java : https://stackify.com/best-practices-exceptions-java/
  • java - Difference between using Throwable and Exception in a try catch - Stack Overflow : https://stackoverflow.com/questions/2274102/difference-between-using-throwable-and-exception-in-a-try-catch

Error

• AssertionError
• LinkageError
  • BootstrapMethodError
  • ClassCircularityError
  • ClassFormatError
    • UnsupportedClassVersionError
  • ExceptionInInitializerError
  • IncompatibleClassChangeError
    • AbstractMethodError
    • IllegalAccessError
    • InstantiationError
    • NoSuchFieldError
    • NoSuchMethodError
  • NoClassDefFoundError
  • UnsatisfiedLinkError
  • VerifyError
• ThreadDeath ( deprecated )
• VirtualMachineError
  • InternalError
  • OutOfMemoryError
  • StackOverflowError
  • UnknownError

Exception

• CloneNotSupportedException
• InterruptedException
• IOException
  • FileNotFoundException
  • SocketException
    • ConnectException
  • UnknownHostException
• ReflectiveOperationException
  • ClassNotFoundException
  • IllegalAccessException
  • InstantiationException
  • InvocationTargetException
  • NoSuchFieldException
  • NoSuchMethodException
• RuntimeException ( Unchecked Exception )
  • ArithmeticException
  • ArrayStoreException
  • ClassCastException
  • ConcurrentModificationException
  • EnumConstantNotPresentException
  • IllegalArgumentException
    • IllegalThreadStateException
    • NumberFormatException
  • IllegalMonitorStateException
  • IllegalStateException
  • IndexOutOfBoundsException
    • ArrayIndexOutOfBoundsException
    • StringIndexOutOfBoundsException
  • NegativeArraySizeException
  • NullPointerException
  • SecurityException
  • TypeNotPresentException
  • UnsupportedOperationException

Checked Exception Arguement

相关争论

• The Trouble with Checked Exceptions
• Kotlin 和 Checked Exception
• 如何评价王垠的《Kotlin和Checked Exception》?
  • Checked Exception 和 Java 标准库自相矛盾 把异常不分青红皂白包装成 RuntimeException 的“设计模式”，早已是 Java 程序员大家都知道的秘密，但标准库中加入 UncheckedIOException 可能算是第一次官方承认这个秘密吧。
  • 应该是用于传递特定信息，触发特定操作的一种编程机制 真正的CE是编程者专门设计的，用于传递特定信息，触发特定操作的一种编程机制。也就是说，throw点和catch点是一个整体设计的两部分，而不是“不管你怎么处理，反正我会throw 它”。反观Java，在类库层面提供的大量通用CE，都是毫无意义的。
  • 不应该去捕获其它函数抛出的异常，而应该去捕获你需要处理的异常 CE之所以没什么用，最根本的原因是，你不应该去捕获其它函数抛出的异常，而应该去捕获你需要处理的异常，在函数签名里写或者不写某个东西对这一目标毫无帮助。需要捕获的异常仅仅包括运行时才会产生的、事先可以预料到的、并且可以恢复的异常，比如磁盘满网络断了之类，其它所有的异常只意味着程序错误，掩盖它们是没用的。

自己的想法

• Fail Fast 策略是合理的
  • 把 Checked Expcetion 包装成 RuntimeException 抛出去就完事了…
  • 像是在 Java 里给方法加 lombok 的注解 @SneakyThrow
• 如果你还想着使用 Checked Exception, 或许可以这么做?
  • 改为抛出其它 RuntimeException 的子类 ( 自行定义, 以区分各种意外情况 )
  • 然后把会抛出的异常, 添加到 JavaDoc @throw 的注释说明中 ( 关心异常的调用方, 自行决定处理或忽略异常 )