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Effective Java 2 study notes Chapter 5 Generic

Article 23-29 of that chapter, focuses on the use of generic programming to the safety benefits as well as the API can be more widely used.

23: Do not use the original code in the new ecological types


Using the original eco-types, such as list, you can not determine the object inside the element in the end what type, will occur ClassCastException error, but can not be found compile and run only when they can. But also has a generic, parameterized can make the compiler to know exactly the type of list, in the formulation and security advantages of both.

There are sub-types of generic rules, List <String> is the original eco-types List of a sub-type, but it is not a parameterized type List <Object> sub-types.

Can not be any element (except null outside) into the Collection <?> C, ie c.add (a) is wrong, c.add (null) was set up

In the uncertain or do not care about the collection element type of situation, the use of unrestricted wildcard, that is, Set <?>

Set <Object> is a parameterized type that can contain any object type

List<Object> strings = new ArrayList<Object>();
                strings.add(1);
                strings.add("d");

Set <?> Is a wildcard that can support any one collection that can contain an unknown object type of a collection of

List<Object> objects = new ArrayList<Object>();
                objects.add(1);
                objects.add("d");
                List<?> s = objects;
                List<String> stings = new ArrayList<String>();
                s = stings;

Set is one of the original ecosystem types, from the generic system is unsafe, just prior to the use of Java 1.5

Two exceptions:

1. In the type of text you must use the original eco-types, not to use parameterized types, List.class, String []. Class and int.class are legitimate, but the List <String>. Class, List <?>. Class is not legal

2.instanceof

24: elimination of non-inspected warning

  1. If you can not eliminate a warning at the same time can prove cause a warning code is type-safe, (and only in such circumstances) can use a @ SuppressWarnings ( "unchecked") annotation to prohibit this warning
  2. The scope should be as small as possible to use SuppressWarnings annotation, do not use class
  3. Not to use the @. . . The time, there are annotated to explain why it is safe to do so

25: List of priority in the array

26: to give priority to generic


The use of generic than using client-side code needed to convert the type of security.

27: to give priority to generic method


A static factory method is particularly suitable for generic technology, the benefits of generic method is similar to the generic, you can ensure that the methods used without conversion.

28: Using a restricted wildcard to enhance the flexibility of API


Limited wildcard

PECS of the principles, producer-extends (List <? Extends T> Priority List <T>), consumer-super (List <? Super T> Priority List <T>)

Do not use a wildcard as the return type

29: to give priority to the safety of heterogeneous types of containers


Map with the type as a key

Under an Effective Java 2 study notes and Chapter 6, enumeration and annotations
标签: lt, string class, arraylist, class string, instanceof, element type, gt c, java 2, generic programming, ecosystem types, generic article, article 23, wildcard, gt class, parameterized types, gt strings, ecological types, generic rules, generic system, safety benefits
分类: Java
时间: 2009-01-15

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