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Created by alfa on June 07, 2011 11:34:26    Last update: June 07, 2011 11:36:37
This is an example that uses dynamic proxies to trace method calls (in logging) and print out elapsed times for them. Because dynamic proxies can only be generated for interfaces, the service classes must be implemented with interface-implementation pairs. Create services A and B. A.java : public interface A { public void service1()... AImpl.java : import java.util.Random; public class AImpl... B.java : public interface B { public void service1()... BImpl.java : public class BImpl implements B { public vo... The call trace proxy: import java.lang.reflect.*; class TraceProx... The performance proxy: import java.lang.reflect.*; class Performan... The service factory: import java.lang.reflect.*; public class Se... The test class: public class Test { public static void main... The output: Entering AImpl.service1 Entering BImpl.service1... The above example has no information...
Created by alfa on June 03, 2011 09:41:03    Last update: June 03, 2011 09:41:03
Dynamic proxy can be used to eliminate the need to stub out unused interface methods. This is an example for a simple SAX content handler for XML parsing. The org.xml.sax.ContentHandler interface requires 11 methods be implemented but we only need three: import java.io.IOException; import java.util.Ar... With a dynamic proxy, we don't need the empty blocks for the unused methods: import java.io.IOException; import java.util.Ar... Equivalently (with anonymous inner class): import java.io.IOException; import java.util.Ar... demo.xml : <breakfast-menu> <food> <name>Belgian W...
Created by alfa on June 02, 2011 15:49:26    Last update: June 02, 2011 15:51:08
Facts: Dynamic proxy classes are generated by the Java runtime, from a list of interfaces given by the user. The generated proxy class implements all interfaces given by the user. The dynamic proxy class is not synthetic . The dynamic proxy class is useless without a user supplied InvocationHandler class, since there's only one constructor for the proxy class and it takes a InvocationHandler as parameter. Example code: import java.lang.reflect.Constructor; import ja... Output: Class: $Proxy0 isSynthetic: false Constructo...
Created by alfa on June 02, 2011 15:26:37    Last update: June 02, 2011 15:26:37
While doing some Java reflection code, I noticed the method Class.isSynthetic() , which the JavaDoc says returns " true if and only if this class is a synthetic class as defined by the Java Language Specification". However, there's no definition of "synthetic class" in the JLS ! The only thing that I can find that remotely resembles a definition is in the JVM spec , where it defines the synthetic attribute : "The Synthetic attribute is a fixed-length attribute in the attributes table of ClassFile (§4.1), field_info (§4.5), and method_info (§4.6) structures. A class member that does not appear in the source code must be marked using a Synthetic attribute." By this definition, a default constructor, which does not appear in the source code, should...
Created by alfa on June 02, 2011 13:51:41    Last update: June 02, 2011 13:51:41
This may be helpful in debugging reflection code. import java.lang.reflect.Modifier; public c...
Created by alfa on June 01, 2011 13:08:36    Last update: June 01, 2011 13:08:36
Code: public class SplitTest { public static void... Output: Split 1: 'a' ' b ' ' c ' 'd ' S...
Created by alfa on May 27, 2011 11:19:29    Last update: May 31, 2011 07:56:26
This is a utility to convert a string value to one of the primitive type values. It is useful in Java reflection code where the value comes in as a string (e.g., from XML parsing), and the type of the value cannot be decided until runtime. import java.util.*; import java.lang.reflect.*;... Note: This method can be extended to convert string to more complex types by writing a converter for the destination type. For example, to convert string to date: public class DateConverter { public static ... Usage: Date d = (Date) ConvertUtil.convert("10/12/2010", ...
Created by alfa on May 24, 2011 14:52:53    Last update: May 26, 2011 19:52:12
import java.lang.reflect.Method; public cla...
Created by alfa on May 25, 2011 20:56:16    Last update: May 25, 2011 20:57:31
The general construct of a non-capturing group is: (?:X) , i.e., add ?: after the opening bracket of an otherwise capturing group. Example code: import java.util.regex.*; public class NonC... Output: Matched: a capturing Subgroup 1: a Subgroup ...
Created by freyo on May 17, 2011 11:13:17    Last update: May 17, 2011 11:13:17
This is an odd-ball content provider in that it doesn't provide database records, but provides a resource as a stream. It can be used to provide media files or XML resources. Start the project with: tools/android create project --package com.android... Create assets directory and add an XML file ( assets/demo.xml ): <? xml version="1.0" encoding="UTF-8"?> <people... Edit the layout ( res/layout/main.xml ): <?xml version="1.0" encoding="utf-8"?> <LinearL... Edit src/com/android/cptest/Dummy.java : package com.android.cptest; import java.io.... Add content provider ( src/com/android/cptest/XmlResource.java ): package com.android.cptest; import java.io.... Update AndroidManifest.xml : <?xml version="1.0" encoding="utf-8"?> <manifes... Add this section to the end of build.xml : <target name="-package-resources"> <ech... Build and install: ant install Screenshot: Remove the Dummy activity ( AndroidManifest.xml ): <?xml version="1.0" encoding="utf-8"?> <manifes... Create a new project for...
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