反射，reflection，听其名就像照镜子一样，可以看见自己也可以看见别人的每一部分。在java语言中这是一个很重要的特性。下面是来自sun公司官网关于反射的介绍：
Reflection is a feature in the Java programming language. It allows an executing Java program to examine or "introspect" upon itself, and manipulate internal properties of the program. For example, it's possible for a Java class to obtain the names of all its members and display them.
The ability to examine and manipulate a Java class from within itself may not sound like very much, but in other programming languages this feature simply doesn't exist. For example, there is no way in a Pascal, C, or C++ program to obtain information about the functions defined within that program.
One tangible use of reflection is in JavaBeans, where software components can be manipulated visually via a builder tool. The tool uses reflection to obtain the properties of Java components (classes) as they are dynamically loaded.
那么解释一下就是，反射是java语言的一个特性，它允程序在运行时（注意不是编译的时候）来进行自我检查并且对内部的成员进行操作。例如它允许一个java的类获取他所有的成员变量和方法并且显示出来。这个能特定我们不常看到，但是在其他的比如C或者C++语言中很不就存在这个特性。一个常见的例子是在JavaBean中，一些组件可以通过一个构造器来操作。这个构造器就是用的反射在动态加载的时候来获取的java中类的属性的。
反射的前传：类类型 Class Class
java中有一个类很特殊，就是Class类，很多朋友在写程序的时候有用过比如Apple.class来查看类型信息，大家就可以把它理解为封装了类的信息，很多解释说Class类没有构造器，其实是有的，只不过它的构造方法是private的（构造函数还有private的？？有，这样是为了禁止开发者去自己创建Class类的实例）。
如果我们拿到一个类的类型信息，就可以利用反射获取其各种成员以及方法了。（注：Class 从JDK1.5版本后就开始更多为泛型服务了）那么我们怎么拿到一个类型的信息呢？假设我们有一个Role类：
[java]
package yui;
/**
* A base class having some attributes and methods
* @author Octobershiner
* @since 2012 3 17
*
* */
public class Role {
private String name;
private String type;
// Constructors
public Role(){
System.out.println("Constructor Role() is invoking");
}
//私有构造器
private Role(String name){
this.name = name;
System.out.println("Constructor Role(String name) is invoking.");
}
//get and set method
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getType() {
return type;
}
public void setType(String type) {
this.type = type;
}
//override the toString method to show the class
@Override
public String toString(){
return "This is a role called "+this.name;
}
}
package yui;
/**
* A base class having some attributes and methods
* @author Octobershiner
* @since 2012 3 17
*
* */
public class Role {
private String name;
private String type;
// Constructors
public Role(){
System.out.println("Constructor Role() is invoking");
}
//私有构造器
private Role(String name){
this.name = name;
System.out.println("Constructor Role(String name) is invoking.");
}
//get and set method
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getType() {
return type;
}
public void setType(String type) {
this.type = type;
}
//override the toString method to show the class
@Override
public String toString(){
return "This