A source of wisdom in times of confusion. Viewed 2k times 1. The serialization proxy pattern has some limitations: It is not compatible with classes that are extendable by their clients, It is not compatible with some classes whose object graphs contain circularities, Serialization is slower than standard approach. Bitte versuchen Sie es erneut. I'd rather see each practice have an immutable chapter number, so you can easily throw them around in conversations, but for this new edition items are once more rearranged and renumbered (as was the case with second edition wrt the first). If you enjoy these notes, please purchase the book! Rezension aus dem Vereinigten Königreich vom 30. … We use cookies and similar tools to enhance your shopping experience, to provide our services, understand how customers use our services so we can make improvements, and display ads. Never do anything time-critical in finalizers. Juni 2019. Avoid finalizer. Ang 2013-06-11 676 words 4 minutes . Effective Java by Bloch, Joshua. Das Buch an sich ist fantastisch. I reference it often and probably this is why I am often asked to say or write more about it. Ask Question Asked 9 years, 9 months ago. Start your free trial. Servere performance penalty for using finalizer, for example, time to create and destroy simple object goes from 5.6ns to 2400ns. Enjoy. Effective Java - Item 8 : Obey the general contract when overriding equals In this item and the following 4 items the author talks about the non-final methods of the Object class - equals, hashcode, toString, clone. As in previous editions, each chapter of Effective Java, Third Edition, consists of several “items,” each presented in the form of a short, stand-alone essay that provides specific advice, insight into Java platform subtleties, and updated code examples. Effective Java Item Preview remove-circle Share or Embed This Item. Select Your Cookie Preferences. Read unlimited* books and audiobooks on the web, iPad, iPhone and Android. Je nach Lieferadresse kann die USt. In this episode, Donn talks about Item #20 in the Effective Java book (third series) by Joshua Bloch. This is NOT a book for beginners to learn Java. They take up thirty-three pages in the language specification [JLS, 15.12.1-3], Don’t use varargs for every method that has a final array parameter; use varargs only when a call really operates on a variable-length sequence of values, Every invocation of a varargs method causes an array allocation and initialization, Use overloaded methods with 2, 3, 4 params to cover most use-cases, otherwise use varargs, Zero-length arrays and empty collections are not performance problems, because they are immutable and only one instance could be used, To document your API properly, you must precede every exported class, interface, constructor, method, and field declaration with a doc comment, If a class is serializable, you should also document its serialized form, The doc comment for a method should describe succinctly the contract between the method and its client, With the exception of methods in classes designed for inheritance, the contract should say, Methods should document pre- and postconditions, side effects, thread safety, exceptions, The first “sentence” of each doc comment should be the summary description, When documenting a generic type or method, be sure to document all type parameters, When documenting an enum type, be sure to document the constants, When documenting an annotation type, be sure to document any members, The most powerful technique for minimizing the scope of a local variable is to declare it where it is first used, Nearly every local variable declaration should contain an initializer (, transforming (no access to index element to apply change), parallel iteration (needed few iterators and control locks), By using a standard library, you take advantage of the knowledge of the experts who wrote it and the experience of those who used it before you, If a flaw were to be discovered, it would be fixed in the next release, With using libraries you don’t have to waste your time writing ad hoc solutions to problems that are only marginally related to your work, Performance of standard libraries tends to improve over time, with no effort on your part, Libraries tend to gain new functionality over time, If performance is crucial, you don’t mind keeping track of the decimal point yourself, and the quantities aren’t too big, use. Miraculously the new edition still is no thicker than its predecessor, which is due to the rather cheap print, i'm afraid. Item 1: Consider static factory methods instead of constructors; Item 2: Consider a builder when faced with many constructor parameters Item 3: Enforce the singleton property with a private constructor or an enum type; Item 4: Enforce noninstantiability with a private constructor Use inheritance when class is designed for inheritance, Class must document its self-use of overridable methods, The only way to test a class designed for inheritance is to write subclasses, Constructors must not invoke overridable methods, Prohibit subclassing in classes that are not designed and documented to be safely subclassed, Prohibit subclassing by making class final, Existing classes can be easily retrofitted to implement a new interface, Interfaces allow the construction of nonhierarchical type frameworks, Interfaces enable safe, powerful functionality enhancements via wrapper classes, Abstract classes are useful for sceletal implementation, You could safely add a method to abstract class with default implementation (, Once an interface is released and widely implemented, it is almost impossible to change, Do not use interface for defining constants, If in a future release the class is modified so that it no longer needs to use the constants, it still must implement the interface to ensure binary compatibility, If a nonfinal class implements a constant interface, all of its subclasses will have their namespaces polluted by the constants in the interface, Add constant to class if they are strongly tied to it, Make constants as enum or noninstantiable utility classes, Tagged class use internal state to indicate its type, Tagged classes are verbose, error-prone, and memory inefficient, Hierarchy classes provide more compile time checks, Function objects are simulate functions in OOP, Primary use of function objects is to implement the Strategy pattern, A nested class should exist only to serve its enclosing class, Static member classes could exist without enclosing, If you declare a member class that does not require access to an enclosing instance, always put the static modifier in its declaration, Anonymous classes have enclosing instances if they are defined ina nonstatic context, Local classes can be declared anywhere a local variable can be declared and have the same scoping rules, Generic types provide compile-time checking for incompatible types, Not needed manual cast to type when you retrieve element from collections, Raw types exists only for backward compatibility, You lose type safety if you use a raw type, Eliminate every unchecked warning that you can, that means your code is typesafe, Every unchecked warning represents the potential for a, Arrays are reified (enforce their element types at runtime), Generics are non-reified and implemented by erasure (enforce types at a compile time, but erased at a runtime), Generic array creation errors at compile time (, Array of non-reified types can not be created, Generic type parameter list, which declares the type parameter, goes between the method’s modifiers and its return type (, Generic methods could infere type of arguments, For maximum flexibility, use wildcard types on input parameters that represent producers or consumers, Do not use wildcard types as return types, it would force use wildcards in the client code, Use explicit types if compiler can’t infere them, if a type parameter appears only once in a method declaration, replace it with a wildcard, Single-element containers could be parametrized (, Compiler won’t complain if you pass one int constant, where another expected, If int constant number is changed, clients should be recompiled, There is no easy way to translate int enum constants into printable strings, There is no reliable way to obtain size or iterate over all the int enum constants in a group, Error is string constant lead to runtime error, Enum types with identically named constants coexist peacefully because each type has its own namespace, You can add or reorder constants in an enum type without recompiling clients, Translate enums into printable strings by calling their, Enum types let you add arbitrary methods and fields and implement arbitrary interfaces, If an enum is generally useful, it should be a top-level class; if its use is tied to a specific top-level class, it should be a member class of that top-level class, Switches on enums are good if you are client user of that enum, Every enum constant associated with int value via, Reordering, adding or deleting enum constant cause problems if you depend on, Just because an enumerated type will be used in sets, there is no reason to represent it with bit fields, ordinal indexing is not typesafe, may cause wrong associations or, If the relationship that you are representing is multidimensional, use, There is no much useful use cases to extend enum functionality, While you cannot write an extensible enum type, you can emulate it by writing an interface to go with a basic enum type that implements the interface, Prior to release 1.5, it was common to use naming patterns to indicate that some program elements demanded special treatment by a tool or framework (name test methods beginning with, No warning about typos, no control over program elements, ugly and fragile approach, With the exception of toolsmiths, most programmers will have no need to define annotation types, Consider using any annotations provided by your IDE or static analysis tools, A marker interface is an interface that contains no method declarations (, Marker interfaces are not marker annotations, Marker interfaces define a type that is implemented by instances of the marked class; marker annotations do not, Marker interfaces can be targeted more precisely by extending that interface, The chief advantage of marker annotations over marker interfaces is that it is possible to add more information to an annotation type after it is already in use, by adding one or more annotation type elements with defaults (Java8 default methods), If you find yourself writing a marker annotation type whose target is, Detect errors and wrong values as soon as possible, nonpublic methods should generally check their parameters using assertions, Unlike normal validity checks, they have no effect and essentially no cost unless you enable them, which you do by passing the, Do not use validity check if it is impractical or performed implicitly in the process of doing the computation, You must program defensively, with the assumption that clients of your class will do their best to destroy its invariants, If you return mutable reference from class, then class is also mutable, To make immutable class, make a defensive copy of each mutable parameter, Defensive copies are made before checking the validity of the parameters and the validity check is performed on the copies rather than on the originals (protect against changes from another thread, TOCTOU, Do not use the clone method to make a defensive copy of a parameter whose type is subclassable by untrusted parties, Defensive copying of parameters is not just for immutable classes, think twice before returning a reference, Defensive copying can have a performance penalty associated with it and isn’t always justified, If the cost of the defensive copy would be prohibitive and the class trusts its clients not to modify the components inappropriately, then the defensive copy may be replaced by documentation outlining the client’s responsibility not to modify the affected components, Too many methods make a class difficult to learn, use, document, test, and maintain, Avoid long parameter lists (four parameters or fewer), Use builder pattern, helper classes or helper methods to avoid long parameter lists, For parameter types, favor interfaces over classes, Prefer two-element enum types to boolean parameters, The choice of which overloaded method to invoke is made at, Selection among overloaded methods is static, while selection among overridden methods is dynamic, A safe, conservative policy is never to export two overloadings with the same number of parameters, The rules that determine which overloading is selected are extremely complex. 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