domingo, abril 19, 2015

Effective Java (Remarked) - Exceptions

Item 57: Use exceptions only for exceptional conditions (safe, stability)

The moral of this story is simple: exceptions are, as their name implies, to be used only for exceptional conditions; they should never be used for ordinary control flow. 

When use? always.

Item 58: Use checked exceptions for recoverable conditions and runtime exceptions for programming errors (safe, stability)

Use checked exceptions for conditions from which the caller can reasonably be expected to recover.  Use runtime exceptions to indicate programming errors. Therefore, all of the unchecked throw- ables you implement should subclass RuntimeException (directly or indirectly).

When use? always.

Item 59: Avoid unnecessary use of checked exceptions (safe, stability)

Checked exceptions are a wonderful feature of the Java programming language. Unlike return codes, they force the programmer to deal with exceptional conditions, greatly enhancing reliability.

When use? always.

Item 60: Favor the use of standard exceptions (safe, stability)

One of the attributes that most strongly distinguishes expert programmers from less experienced ones is that experts strive for and usually achieve a high degree of code reuse. Finally, be aware that choosing which exception to reuse is not always an exact science, as the occasions for use in the table above are not mutually exclusive.

When use? always.

Item 61: Throw exceptions appropriate to the abstraction (safe, stability)

Where possible, the best way to deal with exceptions from lower layers is to avoid them, by ensuring that lower-level methods succeed. In summary, if it isn’t feasible to prevent or to handle exceptions from lower layers, use exception translation, unless the lower-level method happens to guarantee that all of its exceptions are appropriate to the higher level.

When use? it depends.

Item 62: Document all exceptions thrown by each method (safe, stability)

Always declare checked exceptions individually, and document precisely the conditions under which each one is thrown using the Javadoc @throws tag. In summary, document every exception that can be thrown by each method that you write. This is true for unchecked as well as checked exceptions, and for abstract as well as concrete methods. 

When use? always.

Item 63: Include failure-capture information in detail messages (safe, stability)

To capture the failure, the detail message of an exception should contain the values of all parameters and fields that “contributed to the exception.”

When use? always.

Item 64: Strive for failure atomicity (safe, stability)

Generally speaking, a failed method invocation should leave the object in the state that it was in prior to the invocation.

When use? always.

Item 65: Don’t ignore exceptions (safe, stability)

While this advice may seem obvious, it is violated often enough that it bears repeat- ing. When the designers of an API declare a method to throw an exception, they are trying to tell you something. Don’t ignore it! It is easy to ignore exceptions by surrounding a method invocation with a try statement with an empty catch block.

When use? always.

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