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The term reflection is used in the transmission of signals

, and it is used in radio transmission as well as in wired transmission and sound radiation. In addition, the term reflection is also used in object-oriented programming. Reflection

in the context of transmission of electrical, optical and acoustic signals

  1. Reflections occur due to inhomogeneities within a transmission medium, at transitions between two transmission media or at the transition between media with different densities, as in the case of optical fibers. In the case of reflection, a signal component is reflected at the inhomogeneities or the media transitions and travels back in the medium to the source. In the case of conductor-based transmissions, the magnitude of the reflections depends on the impedance difference that exists, for example, in a connector or at the line termination. Cables terminated with the correct impedance, i.e. with the value of the cable impedance, are free of reflections. In the case of reflection, a signal component that is dependent on the impedance difference is reflected from this impedance-dependent junction and superimposed on the original signal. This has the effect of garbling the original signal. In the case of extreme impedance differences, for example in the case of a short circuit or interruption, the garbling can go as far as the cancellation or doubling of the original signal. The measure of the reflection is the reflection factor, which is specified in the capitalized Greek letter gamma.

  2. In optical transmission technology, reflections play a very decisive role in two respects: on the one hand, for the transmission of light in the optical waveguide, and on the other hand, as an interference factor in the case of undesired reflections at inhomogeneities or connections.

    Boundary beam and total reflection at media

    Boundary beam and total reflection at media

    The transmission component is achieved by different densities of core and cladding glass, which results in total reflection of the light beam at the cladding glass and it remains in the core glass. The reflections that negatively affect the transmission occur at inhomogeneities, splices and connectors.

  3. In acoustics, the reflection of sound waves is frequency-dependent and occurs to a greater extent at medium and high sound frequencies. The reflected sound is the reverberation

    . The sound waves are reflected when hitting a body depending on its size, material and surface condition
    Transit time differences in sound reflections

    Transit time differences in sound reflections

    For a hard body with a smooth surface, the angle of incidence is the same as the angle of reflection. In the case of curved bodies, scattering or bundling of the reflected sound occurs depending on the curvature. Absorption occurs with soft materials. If reflected sound waves meet directly radiated sound, the two sound signals overlap. If they are coherent, i.e. if their phase positions are the same, they add up; if they are incoherent, their levels subtract. This effect is called comb filter effect.
Reflection in the

context of object-oriented programming

In object-oriented programming

, reflection designates a way inwhich software can access information

atruntime via appropriate interfaces

thatclarify the structure of the software. The structure of a program is thereby described by so-called meta-information. However, it is not possible to modify the structure of a software on the basis of this information. Introspection has a close relationship to reflection

. Reflectiondescribes a concept of reading classes and objects

thatare held in memory

at runtimeand also modifying them to a limited extent. However, the concept is not supported by all object-oriented programming languages. For example, when translating C++, all specific information - also called meta-information - such as the names of attributes, classes and objects is lost due to the pointer arithmetic used by the compiler. In contrast, in other object-oriented programming languages such as Smalltalk, Python, Ruby, C-Sharp (C#) or Java

, this information is available in a wide variety of forms at the runtime of a program. The term introspection is also frequently mentioned in connection with reflection. This refers to the fact that meta-information provides additional information about a component.Meta-information summarizes information about the structure of a program. This information can be:

  • Which classes exist?
  • What are their subclasses and superclasses?
  • What are their attributes and methods?
  • Which copies of the classes exist?
  • Which operations do they support?
  • What methods are implemented?
Provided that this meta-information is available at the runtime of a software, it can be used, for example, to define rules for mapping classes to the tables of a relational database. Object Relational Mapping tools often use the mechanism of reflection to generate information about the structure of a software - the classes and their related objects - at runtime. An example of this is Hibernate - which is an open sourceframework

that maps objects to relational databases. Inthis context, we also speak of meta-objects when the elements - classes, attributes and methods - of a software's structure are available as objects at a software's runtime

. Programming languages such as Java or the proprietary language C# offer corresponding packages or namespaces for programming reflection - in Java it is the package java.lang.reflect and in the .NET framework

thenamespace System

.Reflection. In Java, reflection can be used not only to determine information but also to modify it. However, this only applies to the data of the program and not to its structure as a whole. Thus, it is not possible to insert new methods or create additional classes dynamically at runtime. However, you can change the attributes of an object or call its methods dynamically. Reflection is often used with respect to persisting objects - inserting objects into a database at runtime. The concept of reflection is also used in Java beans, debugging programs, and GUI builders, which is why these programs are often referred to as meta programs. So-called meta programs always work on classes and objects of external programs.

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Englisch: reflection
Updated at: 17.11.2019
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