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. 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 секс ксоникс java.
That is, the method секс ксоникс java of class java. Stack are listed, along with their fully qualified parameter and return types. This program loads the specified class using class. Method is a class representing a single class method. The reflection classes, such as Methodare found in java. There are three steps that must be followed to use these classes. The first step is to obtain a java. Class object for the class that you want to manipulate.
Class is used to represent classes and interfaces in a running Секс ксоникс java program. The second step is to call a method such as getDeclaredMethodsto get a list of all the methods declared by the class. Секс ксоникс java this information is in hand, then the third step is to use the reflection API to manipulate the information.
For example, the sequence:. In the examples below, the three steps are combined to present self contained illustrations of how to tackle specific applications using reflection. Once Class information is секс ксоникс java hand, often the next step is to ask basic questions about the Class object. For example, the Class.
One of the most valuable and basic uses of reflection is to find out секс ксоникс java methods are defined within a class. To do this the following code can be used:.
Each of these types, whether they are fundamental or class types, is in turn represented by a Class descriptor. To do this, the following code can be used:.
So far the examples that have been presented секс ксоникс java relate to obtaining class information. Once this method has been found and captured into a Method object, it is invoked upon an object instance of the appropriate type. To invoke a method, a parameter list must be constructed, with the fundamental integer values 37 and 47 wrapped in Integer секс ксоникс java.
The return value 84 is also wrapped in an Integer object. There is no equivalent to method invocation for constructors, because invoking a constructor is equivalent to creating a new object to be the most precise, creating a new object involves both memory allocation and object construction.
So the секс ксоникс java equivalent to the previous example is to say:. Another use of reflection is to change the values of data fields in objects. The value of this секс ксоникс java again derived from the dynamic nature of reflection, where a field can be looked up by name in an executing program and then have its value changed. This is illustrated by the following example:.
One final use of reflection is in creating and manipulating arrays. Arrays in the Java language are a specialized type of class, and an array reference can be assigned to an Object reference. Note that the type of array that is created is dynamic, and does not have to be known at compile time. Java reflection is useful because it supports dynamic retrieval of information about classes and data structures by name, and allows for their manipulation within an executing Java program.
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A Simple Example To see how reflection works, consider this simple example: Stack the output is: Object public synchronized java. Object That is, the method names of class java.
One way of obtaining a Class object is to say: String" ; to get the Class object for String. Another approach is to use: TYPE; to obtain Class information on fundamental types. The latter approach accesses the predefined Секс ксоникс java field of the wrapper such as Integer for the fundamental type. For example, the sequence: Simulating the instanceof Operator Once Class information is in hand, often the next step is to ask basic questions about the Секс ксоникс java object.
Integer 37 is not, but секс ксоникс java A is. Finding Out About Methods of a Class One of the most valuable and basic uses of reflection is to find out what methods are defined within a class. To do this the following code can be used: These include public, protected, package, and private methods.
If you use getMethods in the секс ксоникс java instead of getDeclaredMethodsyou can also obtain information for inherited methods. The output of the program is: Object param 1 int exc 0 class java.
When this program is run, the output is: To do this, the following code can be used: One new секс ксоникс java is the use of Modifier.
This секс ксоникс java a reflection class that represents the modifiers found on a field member, for example " private int ". The modifiers themselves are represented by an integer, and Modifier.
Invoking Methods by Name So far the examples that have been presented all relate to obtaining class information. To see how this works, consider the following example: That is, the name of the method is specified during execution this might be секс ксоникс java by a JavaBeans development environment, for example. The above program shows a way of doing this.
Creating New Objects There is no equivalent to method invocation for constructors, because invoking a секс ксоникс java is equivalent to creating a new object to be the most precise, creating a new object involves both memory allocation and object construction.
So the nearest equivalent to the previous example is to say: Changing Values of Fields Another use of reflection is to change the values of data fields in objects. This is illustrated by the following example: Using Arrays One final use of reflection is in creating and manipulating arrays.
To see how arrays work, consider the following example: The value is retrieved секс ксоникс java displayed. A секс ксоникс java complex manipulation of arrays is illustrated by the following code: Note here that a multi-dimensional array is секс ксоникс java an array of arrays, so that, for example, after the first Array.
This is peeled back once again to obtain a long array, and the 10th slot in that array is set using Array. Summary Java reflection is useful because it supports dynamic retrieval of information about classes and data structures by name, and allows for their manipulation within an executing Java program. Contact Us US Sales: News Newsroom Magazines Acquisitions Blogs.
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