Java Reflection API& Reference Object

Prepared by: Group 5

Nguyen Dang Khoa 0712220

Diep Lan Quynh 0712360

Le Thi Nhu Quynh 0712358

HoChiMinh University of ScienceJava Programming Course

December 2010

Agenda

Introduction Java Reflection API

java.lang.Class class

Class Member

Array and Enum

Advantage & Disadvantage

Plug-in Programming

Introduction

• What does “Reflection” mean ?• What’s Java Reflection API ?• Java Reflection API• Usage• “Hello Reflection” Demo

3

Introduction…

• What does “Reflection” mean ?In computer science, reflection is the process by which a computer program can observe and modify its own structure and behavior at runtime[1].

4

Introduction…

5

An Java program contains many objects. Java Reflection API includes classes, interfaces support developer can retrieve and manipulate its object at runtime.

What’s Java Reflection API?

Introduction …

• Java Reflection APIInterface

java.lang.reflect.AnnotatedElement java.lang.reflect.GenericDeclaration java.lang.reflect.InvocationHandler java.lang.reflect.Member java.lang.reflect.Type

6

Introduction …

• Java Reflection API …Class

• java.lang.reflect.AccessibleObject java.lang.reflect.Constructor java.lang.reflect.Field java.lang.reflect.Method

• java.lang.reflect.Array• java.lang.reflect.Modifier• java.lang.reflect.Proxy

7

Introduction …

• Java Reflection API …Exception

java.lang.reflect.InvocationTargetException java.lang.reflect.MalformedParameterizedTypeException

java.lang.reflect.UndeclaredThrowableException

Errorjava.lang.reflect.GenericSignatureFormatError

8

Introduction…

• Usage Program Extensibility IDE’s Visual Assistant Visual Debugger & Tester Tools Object Relational Mapping Application Server Deploy Configuration

9

Agenda

Introduction Java Reflection API

java.lang.Class class

Class Member

Array and Enum

Advantage & Disadvantage

Plug-in Programming

java.lang.Class class

• Kind of Java types• Class object• How to get a Class object • How to get Class’ members object• Instantiate a new object from its Class

11

java.lang.Class class …

Kind of Java types• Primitive type

e.g : int, double, float, short, long, byte, char, void• Reference type

e.g : class, interface, array, enum, annotation

12

java.lang.Class class…

Class object• Instances of the class Class represent

classes and interfaces in a running Java application.

• Has no public constructor.• Are constructed automatically by the Java

Virtual Machine as classes are loaded and by calls to the defineClass method in the class loader.

13

java.lang.Class class…

How to get a Class object• getClass() method• .class syntax• forName() static method • .TYPE syntax• Other methods

14

java.lang.Class class…

How to get Class’ members object

15

Get Constructors

Constructor<T> getConstructor(Class<T>… parameterTypes)

Constructor<?> [] getConstructors()

Constructor<T> getDeclaredConstructor(Class<T>… parameterTypes)

Constructor<?> [] getDeclaredConstructors()Get Fields Field getField(String fieldName)Field [] getFields()Field getDeclaredField(String fieldName)Field [] getDeclaredFields()

java.lang.Class class…

How to get Class’ members object

16

Get Methods

Method getMethod(String name, Class<T>… parameterTypes)

Method [] getMethods()

Method getDeclaredMethod(String name, Class<T>… parameterTypes)

Method [] getDeclaredMethods();Get Modifiers int getModifiers()

java.lang.Class class…

How to get Class’ members object

17

Get Package

Package getPackage()

Other methods

Ref : JDK Document

Agenda

Introduction Java Reflection API

java.lang.Class class

Class Member

Array and Enum

Advantage & Disadvantage

Plug-in Programming

Class member

• java.lang.reflect Constructor Field Method

19

Class member…

• ConstructorGet information

• Class<T> getDeclaringClass()• Class<T> [] getParameterTypes()• int getModifiers()

Instantiate new object• newInstance(Object … initArgs)

20

Class member…

• FieldGet information

Class<T> getDeclaringClass() Class<T> getType() int getModifiers()

Get field’s value of an object Object get(Object obj)

Set field’s value of an object• set(Object obj, Object value)

21

Class member…

• Getting Field’s Value Example

22

Class c = Integer.class; //get a private instant field Field field = c.getDeclaredField("value"); field.setAccessible(true); System.out.format(field.get(new Integer(10)));

//get a public static field field = c.getField("MAX_VALUE"); System.out.format(field.get(null));

Class member…

• Setting Field’s Value Example

23

Class c = Integer.class; Integer i = new Integer(10);//get a private instant field Field field = c.getDeclaredField("value"); field.setAccessible(true); System.out.format(field.set(i, new Integer(20)));

//get a public static field field = c.getField("MAX_VALUE"); System.out.format(field.set(null, new Integer(20)));

Class member…

• Method–Get information

• Class<T> getDeclaringClass()• Class<T> [] getParameterTypes()• int getModifiers()• Class<T> getReturnType()

– Invoke method• Object invoke(Object obj, Object … initArgs)

24

Class member…

• Invoke a method example

25

Method f = Math.class.getMethod("sqrt", new Class[]{double.class});

Object[] args = {new Double(10)};//invoke a static method Double d = (Double) f.invoke(null, args); double y = d.doubleValue(); System.out.println(y);

Agenda

Introduction Java Reflection API

java.lang.Class class

Class Member

Array and Enum

Advantage & Disadvantage

Plug-in Programming

Array and Enum

• Array (java.lang.reflect package) Get array’s information Instantiate a new array dynamically Set/Get array component’s value

• Enum Get enum’s information Set/Get enum component’s value

27

Agenda

Introduction Java Reflection API

java.lang.Class class

Class Member

Array and Enum

Plug-in Programming

Advantage & Disadvantage

Plug-in Programming

29

ApplicationApplication

Plugin Container

SQL MySQL Oracle

Advantage & Disadvantage

Advantage• Dynamic Programming• Avoid hard-coding

Disadvantage• Performance• Security

30

31

Q & AThanks you!