Reflection in Java Manuel Oriol - May 3rd, 2007 Introductory - PowerPoint PPT Presentation

Reflection in Java Manuel Oriol - May 3rd, 2007

Introductory Example 2

Reflection? • Introspection • Dynamic reflexive invocations • Meta-Classes: classes are instances of a meta-class 3

In Java • Limited to introspection and reflexive invocation • Package: java.lang.reflect • class Class, class Method, class Field • Built-In: instanceof 4

Class Object • getClass() 5

Class Class<?> • static forName • getClasses • getConstructor/getConstructors • getField/geFields • getMethod/getMethods • getModifiers • getName • isInstance 6

Class Field • get, getInt, getDouble... • getDeclaringClass • getModifiers • getName • getType • set(obj,value) 7

Example is equivalent to: 8

Class Constructor • getDeclaringClass • getModifiers • getName • getTypeParameters • isVarArgs • newInstance 9

Example is equivalent to: 10

Class Method • getDeclaringClass • getModifiers • getName • getTypeParameters • isVarArgs • invoke(obj,args...) 11

Example is equivalent to: 12

Deeper Example 13

Proxy Classes • Meant to be used as a simple way to implement some interfaces. • Created at runtime • Use a handler to treat requests • instanceof is true with a proxy • cast is working correctly 14

Class Proxy • getInvocationHandler • getProxyClass • isProxyClass • newProxyInstance 15

InvocationHandler • invoke 16

Example 17

Performance (1/3) 18

Performances (2/3) for the JIT “T esting direct calls” 19

Performance (3/3) “T esting reflexive calls” 20

Result 10 -2 10 -1 ~ 10 10 2 10 3 Mean time (ns) for regular call: 7 Mean time (ns) for reflexive call: 262 ------- Slowdown factor: 33x 21

Security Issues with Reflection ... 22

So... what about visibility of the method??? • Short answer: it is respected through the SecurityException • Long answer? If you define your own SecurityManager and your own ClassLoader then you can do what you want!!! 23