[Java Basics2] Iterable, Socket, Reflection, Proxy, Factory DP
Parent interface of Collection: Iterable Interface
A class that implements the Iterable
can be used with the new for-loop.
The Iterable
interface has only one method:
public interface Iterable<T> {
public Iterator<T> iterator();
}
It is possible to use your own collection type classes with the new for-loop. To do so, your class must implement thejava.lang.Iterable<E>
interface. Here is a very basic example:
public class MyCollection<E> implements Iterable<E>{ public Iterator<E> iterator() {
return new MyIterator<E>();
}
}
And here is the corresponding implementation skeleton of the MyIterator
class:
public class MyIterator <T> implements Iterator<T> { public boolean hasNext() { //implement...
} public T next() {
//implement...;
} public void remove() {
//implement... if supported.
}
} 迭代器应用:
list l = new ArrayList();
l.add("aa");
l.add("bb");
l.add("cc");
for (Iterator iter = l.iterator(); iter.hasNext();) {
String str = (String)iter.next();
System.out.println(str);
}
Java sockets
A socket is one end-point of a two-way communication link between two programs running on the network. Socket classes are used to represent the connection between a client program and a server program. The java.net package provides two classes--Socket and ServerSocket--that implement the client side of the connection and the server side of the connection, respectively.
总: Client[port] <----->Server[listening port, communication port] ,
Server side: ServerSocket serverSocket = new ServerSocket(5000); //Server will be listening to requests from clients on port 5000
Client side: Socket chatSocket = new Socket("192.1.168.100", 5000); //The server is running on port 5000 at 192.1.168.100
Socket sock = serverSocket.accept(); //Server will return a new port to communicate with clients
InputStreamReader reader = new InputStreamReader(chatSocket.getInputStream());
BufferedReader breader = new BufferedReader(reader);
String msg = breader.readLine();
Reflection
1, Get Class: 如果compile time已知class,那可以A.class。如果runtime才知class name,那可以Class.forName("className");
Get Class以后就可以获取这个Class的所有信息,例如.getMethods(), .getConstructors(), .getInterfaces(), .getFields(), .getAnnotations()...
2, Get constructor以后可以Instantiate object:
Constructor constructor=A.class.getConstructor(String.class);
A a= (A) constructor.newInstance("StringArgument");
3, Get fields以后可以get 或set object里的这个field:
Field someField = A.class.getField("FieldName"); //.getField()方法只能获取public fields
A a = new A();
Object value = someField.get(a);
someField.set(a, value);
4,Get method以后可以invoke这个method on some object:
Method method = A.class.getMethod("MethodName", String.class); //.getMethod()方法只能获取public methods
Object returnValue = method.invoke(new A(), "StringArgument");
5, Get private field/method
Field privateField = A.class.getDeclaredField("FieldName"); //or .getDeclaredMethod("MethodName");
privateField.setAccessible(true);
Object fieldValue = privateField.get(new A());
6, Get annotations
Annotations可以是在class上,或者method, field, parameter上...
在定义自己的@interface的时候,如果@Retention(RetentionPolicy.RUNTIME)表示在runtime时可以获取这个annotation.
Annotation annotation = A.class.getAnnotation(MyAnnotation.class);
if(annotation instanceof MyAnnotation) {annotation.getName();...}
Proxy
To create dynamic implementations of interface at runtime with the help of reflection.
InvocationHandler handler = new MyInvocationHandler(); //implement .invoke()方法
MyInterface proxy = (MyInterface) Proxy.newProxyInstance(MyInterface.class.getClassLoader(), new Class[] {MyInterface.class}, handler);
links
http://tutorials.jenkov.com/java-concurrency/blocking-queues.html
http://docs.oracle.com/javase/tutorial/essential/io/file.html
http://stackoverflow.com/questions/19966662/java-memory-model-and-final-fields
Factory design pattern
简单工厂模式就是客户选择一个工厂来生产不同区域的产品,The Simple Factory isn’t actually a Design Pattern; it’s more of a programming idiom.
由一个工厂来生产不同区域的产品,当区域太多时逻辑就变很多,所以工厂方法模式就是出现多个工厂来生产对应区域的不同类型的产品,所以这里有抽象工厂和具体工厂的分别。
例子:(Abstract class)PizzaStore-->(Sub classes)ItalyPizzaStore, SpainPizzaStore, SwedenPizzaStore...
defined orderPizza() method defined different details of createPizza() method to make ItalianStylePizza...
The Factory Method Pattern defines an interface for creating an object, but lets subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to subclasses.
Examples:java.util.ResourceBundle#getBundle(), java.util.Calendar#getInstance().
对于抽象工厂,Abstract factory记住,Product interface->Product1, Product2..., Factory Interface->Factory1, Factory2, ...These factories will produces different combinations of products, so the abstract factory will return you the correct Factory# to use.
抽象工厂的区别是这里不只有一种产品(前面的pizza),还有薯条,比如具体工厂A生产芝士皮萨配细薯条, 工厂B生产西兰花皮萨配粗薯条。所以产品方面会有多个:抽象产品Pizza&Fries,具体产品CheesePizza_BroccoliPizza & ..。
An Abstract Factory gives us an interface for creating a family of products. By writing code that uses this interface, we decouple our code from the actual factory that creates the products. That allows us to implement a variety of factories that produce products meant for different contexts—such as different regions, different operating systems, or different look and feels.
This pattern separates the details of implementation of a set of objects from their general usage and relies on object composition, as object creation is implemented in methods exposed in the factory interface.
多个抽象产品,多个抽象factory,一个factory producer class。
javax.xml.parsers.DocumentBuilderFactory#newInstance()
javax.xml.transform.TransformerFactory#newInstance()
- javax.xml.xpath.XPathFactory#newInstance()
Advantage:
- Factory methods eliminate the need to bind application-specific classes into your code.
- The code only deals with the product interfaces; therefore, it can work with any user-defined concrete product classes.
- Factory methods provide hooks for sub-classes to create different concrete products. In the example below, the Factory method
MakeUISpecificCtrls
provides the hook for creating the UI component specific controls. In the defaultCUIComponent
, a simple edit control is created; however, we can change this behavior in the derived class to create an edit control which accepts only floating point values. - Factory methods connect parallel class hierarchies in such a way that it localizes the knowledge of which classes belong together. In the example below, the
CUIComponent
andCEditCtrl
class hierarchies can be connected with each other. Also notice how the Factory method defines the connection between the two class hierarchies.
Disadvantage:
- A potential disadvantage of Factory methods is that clients might have to sub-class the creator class just to create a particular concrete product object.
- Subclassing is fine when the client has to subclass the creator class anyway, but otherwise, the client now must deal with another point of evolution.
- In Factory Method pattern, the factory used for creating the objects is bound with the client code, i.e., it is difficult to use a different factory for creating objects.
Java runtime exception & checked exception
Runtime: NullPointerException, IndexOutOfBoundException, ArithmeticException(除0), ClassCastException, IllegalArgumentException.
CheckedException: 除了以上的这几个runtime的,其余都是checked,例如IOException, ClassNotFoundException, SQLException...
Clone() method:
When the clone
method is invoked upon an array, it returns a reference to a new array which contains (or references) the same elements as the source array.
int[] a = {1,2,3};
int[] b = a.clone();
System.out.println(a == b ? "Same Instance":"Different Instance");
//Outputs different instance
If were to modify int[] b
the changes would not be reflected on int[] a
since the two are separate object instances. This becomes slightly more complicated when the source array contains objects. The clone
method will return a reference to a new array, which references the same objects as the source array.
Dog[] myDogs = new Dog[2];
myDogs[0] = new Dog("Wolf");
myDogs[1] = new Dog("Pepper");
Dog[] myDogsClone = myDogs.clone();
System.out.println(myDogs[0] == myDogsClone[0] ? "Same":"Different"); //same
myDogsClone[0].setName("Ruff"); System.out.println(myDogs[0].getName()); //Outputs Ruff, However, changes to the array itself will only affect that array.
所以对于只包含primitive type的array, clone()就直接返回一个新的object,里面的内容和原object没关系。但如果原array里包含的是Object, 那么新的array Object里包含的是指向同一些objects的reference, 所以对新array里elements做修改会影响原array的Object。
[Java Basics2] Iterable, Socket, Reflection, Proxy, Factory DP的更多相关文章
- HibernateProxy异常处理 java.lang.UnsupportedOperationException: Attempted to serialize java.lang.Class: org.hibernate.proxy.HibernateProxy. Forgot to register a type adapter?
这里使用google的Gson包做JSON转换,因为较早的1.4版本的FieldAttributes类中没有getDeclaringClass()这个方法,这个方法是获取field所属的类,在我的排除 ...
- Attempted to serialize java.lang.Class: org.hibernate.proxy.HibernateProxy. Forgot to register a type adapter?
当我们使用gson 转对象时,并且这个对象中有一些属性是懒加载时如 @Entity @Table(name = "user") public class User { @Id @C ...
- Java设计模式之工厂模式(Factory模式)介绍(转载)
原文见:http://www.jb51.net/article/62068.htm 这篇文章主要介绍了Java设计模式之工厂模式(Factory模式)介绍,本文讲解了为何使用工厂模式.工厂方法.抽象工 ...
- java.lang.NoClassDefFoundError: javassist/util/proxy/MethodFilter
转自:https://blog.csdn.net/rchm8519/article/details/23788053 1. ERROR - Context initialization failedo ...
- Java中的Socket的用法
Java中的Socket的用法 Java中的Socket分为普通的Socket和NioSocket. 普通Socket的用法 Java中的 ...
- Java-Spring:java.lang.ClassCastException: com.sun.proxy.$Proxy* cannot be cast to***问题解决方案
java.lang.ClassCastException: com.sun.proxy.$Proxy* cannot be cast to***问题解决方案 临床表现: 病例: 定义代理类: @Tra ...
- java.lang.ClassCastException: com.sun.proxy.$Proxy32 cannot be cast to com.bkc.bpmp.core.cache.MemcachedManager
java.lang.ClassCastException: com.sun.proxy.$Proxy32 cannot be cast to com.bkc.bpmp.core.cache.Memca ...
- Java反射机制(Reflection)
Java反射机制(Reflection) 一.反射机制是什么 Java反射机制是程序在运行过程中,对于任意一个类都能够知道这个类的所有属性和方法;对于任意一个对象都能够调用它的任意一个方法和属性,这种 ...
- java网络编程socket解析
转载:http://www.blogjava.net/landon/archive/2013/07/02/401137.html Java网络编程精解笔记2:Socket详解 Socket用法详解 在 ...
随机推荐
- 【转】malloc与free的底层实现
本文转自:http://blog.163.com/xychenbaihu@yeah/blog/static/132229655201210975312473/ 如何查看进程发生缺页中断的次数? 用ps ...
- Mac OS下pip安装 pillow
sudo pip install pil报错如下:/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Develo ...
- 查看SQL SERVER数据库运行参数和连接数
---查看当前数据库系统所有请求情况.我只列出了我认为比较重要有助于我解决问题的字段. SELECT ds.session_id, ds.status, Db_name(dr.database_id) ...
- Pycharm使用问题# 内部Terminal
1.Windows XP并不支持内部Terminal
- Python3.X新特性之print和exec
print print 现在是一个函数,不再是一个语句.<语法更为清晰> 实例1 打开文件 log.txt 以便进行写入并将对象指定给 fid.然后利用 print将一个字符串重定向给文件 ...
- Android SharePreference 在主进程和次进程间共享数据不同步出错
SharedPreference作为android五大存储(网络,数据库,文件,SharedPreference,contentProvider)之中最方便使用的一个,从类名上来看就不是一个存储大 ...
- oracle表空间不足相关问题解决办法
欢迎和大家交流技术相关问题: 邮箱: jiangxinnju@163.com 博客园地址: http://www.cnblogs.com/jiangxinnju GitHub地址: https://g ...
- 在eclipse中导入weka(小白在路上)
第一步:新建一个java工程,new->javaproject,假设工程名为wekatest 第二步:导入weka.jar 第三步:src关联 导入后有许多的.class文件,直接双击打开是看不 ...
- Java Web基础:JSP基础概念
JSP介绍 JSP全称是Java Server Pages,它和Servlet都是Sun公司定义的用于开发动态Web资源的技术,它解决了Servlet输出流排版复杂和难以维护的问题.JSP完美融合了H ...
- Java 编程入门(词汇表)
抽象类(abstract class):抽象类不能创建对象,主要用来创建子类.Java中的抽象类使用 abstract 修饰符定义. 抽象数据类型(abstract data type ADT):抽象 ...