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

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

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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

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Reflection in Java

Manuel Oriol - May 3rd, 2007

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2

Introductory Example

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Reflection?

  • Introspection
  • Dynamic reflexive invocations
  • Meta-Classes: classes are instances of a

meta-class

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In Java

  • Limited to introspection and reflexive

invocation

  • Package: java.lang.reflect
  • class Class, class Method, class Field
  • Built-In: instanceof

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Class Object

  • getClass()

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Class Class<?>

  • static forName
  • getClasses
  • getConstructor/getConstructors
  • getField/geFields
  • getMethod/getMethods
  • getModifiers
  • getName
  • isInstance

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Class Field

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

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Example

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is equivalent to:

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Class Constructor

  • getDeclaringClass
  • getModifiers
  • getName
  • getTypeParameters
  • isVarArgs
  • newInstance

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Example

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is equivalent to:

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Class Method

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

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Example

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is equivalent to:

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Deeper Example

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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

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Class Proxy

  • getInvocationHandler
  • getProxyClass
  • isProxyClass
  • newProxyInstance

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InvocationHandler

  • invoke

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Example

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Performance (1/3)

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Performances (2/3)

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“T esting direct calls” for the JIT

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Performance (3/3)

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“T esting reflexive calls”

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Result

Mean time (ns) for regular call: 7 Mean time (ns) for reflexive call: 262

  • Slowdown factor: 33x

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10-2 10-1 ~ 10 102 103

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Security Issues with Reflection

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...

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So... what about visibility

  • f the method???

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  • 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!!!