Summary

Chapter 3 Methods Common To All Objects

Item 10

The instanceof operator is specified to return false if its first operand is null, regardless of what type appears in the second operand [JLS, 15.20.2]. Therefore, the type check will return false if null is passed in, so you don’t need an explicit null check.

Chapter 4 Class and Interface

Item 15

Instance fields of public classes should rarely be public (Item 16). If an instance field is nonfinal or is a reference to a mutable object, then by making it public, you give up the ability to limit the values that can be stored in the field. This means you give up the ability to enforce invariants involving the field. Also, you give up the ability to take any action when the field is modified, so classes with public mutable fields are not generally thread-safe.

Item 16

In summary, public classes should never expose mutable fields.

Chapter 10 Exception

Item 69/70

Use checked exceptions for conditions from which the caller can reasonably be expected to recover. If a program throws an unchecked exception or an error, it is generally the case that recovery is impossible and continued execution would do more harm than good. If a program does not catch such a throwable, it will cause the current thread to halt with an appropriate error message.

To summarize, throw checked exceptions for recoverable conditions and unchecked exceptions for programming errors. When in doubt, throw unchecked exceptions. Don’t define any throwables that are neither checked exceptions nor runtime exceptions. Provide methods on your checked exceptions to aid in recovery.

Item 71

If a method throws checked exceptions, the code that invokes it must handle them in one or more catch blocks, or declare that it throws them and let them propagate outward. Either way, it places a burden on the user of the API. The burden increased in Java 8, as methods throwing checked exceptions can’t be used directly in streams

Item 72

• Do not reuse Exception, RuntimeException, Throwable, or Error directly.
• Remember that exceptions are serializable (Chapter 12). That alone is reason not to write your own exception class without good reason.

Item 75

To capture a failure, the detail message of an exception should contain the values of all parameters and fields that contributed to the exception. do not include passwords, encryption keys, and the like in detail messages.

Item 76

Generally speaking, a failed method invocation should leave the object in the state that it was in prior to the invocation. A method with this property is said to be failure-atomic.

the most common way to achieve failure atomicity is to check parameters for validity before performing the operation (Item 49).