Annotation format error, assertion error, ... , virtual machine error 不需要在 編譯期檢查的原因如下： error 隨處都有可能發生，寫出這些 error 會讓程式碼很雜亂，而且發生之後幾乎不可 能修復。 Arithmetic exception, buffer overflow exception, ..., unsupported operation exception 不需要在編譯期檢查的原因如下： 一個正確的程式不會發生 runtime exception，寫出這些 runtime exception 反而變成 一種累贅。 舉例而言，在 circular data structure 永遠都不該出現 null，但是錯誤的實作可能 會在執行的過程中拋出 NullPointerException，當 runtime exception 出現的同時， 通常代表程式寫錯了！ 其他 exception 都必須在編譯期檢查的原因如下： 即使是一個正確的程式，仍然會有例外發生，明確地寫出哪些方法會拋出哪些例外，並 且寫出這些例外要做什麼樣的處理，整個錯誤處理程序可以提升系統的可靠度。 舉例而言，sleep 方法很可能會被另一個執行緒以 interrupt 方法打斷，此時 sleep 會拋出 interrupted exception 讓對應的錯誤處理程序接手，進行適當的動作回應另一 個執行緒的中斷行為。 回到問題原點：為什麼我特地把 sleep 重新包裝成為一個只會拋出 runtime exception 的方法？ 原因是在某些正確實作的程式下，sleep 方法永遠都不應該被 interrupted 。如果哪天 sleep 方法被 interrupted 那肯定是程式哪邊寫錯了！ -- 以下是我的參考資料與節錄部分內容 http://java.sun.com/docs/books/jls/third_edition/html/exceptions.html 11.2.4 Why Errors are Not Checked Those unchecked exception classes which are the error classes (Error and its subclasses) are exempted from compile-time checking because they can occur at many points in the program and recovery from them is difficult or impossible. A program declaring such exceptions would be cluttered, pointlessly. 11.2.5 Why Runtime Exceptions are Not Checked The runtime exception classes (RuntimeException and its subclasses) are exempted from compile-time checking because, in the judgment of the designers of the Java programming language, having to declare such exceptions would not aid significantly in establishing the correctness of programs. Many of the operations and constructs of the Java programming language can result in runtime exceptions. The information available to a compiler, and the level of analysis the compiler performs, are usually not sufficient to establish that such run-time exceptions cannot occur, even though this may be obvious to the programmer. Requiring such exception classes to be declared would simply be an irritation to programmers. For example, certain code might implement a circular data structure that, by construction, can never involve null references; the programmer can then be certain that a NullPointerException cannot occur, but it would be difficult for a compiler to prove it. The theorem-proving technology that is needed to establish such global properties of data structures is beyond the scope of this specification. --

※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 140.116.247.13 重新排一次了，可能會比較正常 ※ 編輯: H45 來自: 140.116.247.13 (10/06 12:58)