The example that we are going to use again and again throughout the article, is accessing the title of watchmen inside the catalog and convert it to upper case. Homogeneous maps of unknown size are usually represented by hash maps, while heterogeneous maps of fixed sized are usually represented with classes. Other pieces of data are heterogeneous maps of fixed size (e.g. Some pieces of data in our catalog are homogeneous maps of unknown size (e.g. Here is an example of a catalog data in JSON: Let’s take as an example data from a library catalog with a single book. Using Java Reflection you can inspect the fields (member variables) of classes and get / set them at runtime.
Java reflection get name of instance field how to#
Towards the end of the article, we suggest how to keep a bit of type safety even when data access is dynamic.
Java reflection get name of instance field code#
But, when dealing with generic types, the following line of code wont compile (when T is a generic type): Java. The purpose of this article is to illustrate various ways to access data dynamically in Java, both with classes and maps. For getting a types name in Java we call the getTypeName function on the types class. It includes methods for discovering the name of the class (getName). For every type of object JVM creates an immutable instance of which provides methods to examine the runtime properties of the object including its members and type information. IllegalAccessException - if this Field object is enforcing Java language access control and the underlying field is either inaccessible or final.
This method is equivalent to set (obj, fObj), where fObj is a Float object and fObj.floatValue () f.
The first two principles of Data-Oriented programming (DOP) seem to be in the spirit of the newest additions to Java (e.g data records in Java 14): To what extent Data-Oriented programming is applicable in a statically-typed language like Java? A Field permits widening conversions to occur during a get or set access operation. Before returning the value, GetValue checks to see if the user has access permission.An interesting question in the context of information systems is: The reflected field may be a class (static) field or an instance field. For example, if the field holds a Boolean primitive value, an instance of Object with the appropriate Boolean value is returned. Note that the return type of GetValue is Object. For non-static fields, obj should be an instance of a class that inherits or declares the field. ' Displaying the values of the fields of FieldsClass: using namespace System įieldsClass^ fieldsInst = gcnew FieldsClass Īrray^ fields = fieldsType->GetFields(static_cast(BindingFlags::Public | BindingFlags::Instance)) Ĭonsole::WriteLine("Displaying the values of the fields of :", fieldsType)įor i As Integer = 0 To fields.Length - 1įields(i).Name, fields(i).GetValue(fieldsInst), vbTab) The newInstance() method on constructor object is used to instantiate a new instance of the class. The following example retrieves an array of FieldInfo objects that represents the fields of the FieldsClass type, and then calls the GetValue to display the value of each field for the fieldsInst object. ' The example displays the following output: The example displays the following output:įieldInfo fld = typeof(Example).GetField("val") ĭim fld As FieldInfo = GetType(Example).GetField("val") using namespace System įieldInfo^ fld = Example::typeid->GetField( "val" ) Ĭonsole::WriteLine(fld->GetValue(nullptr) ) It then uses the reflection method Class.getDeclaredField() to obtain a field given the fields class and name.
Note that the value of the obj argument is null. This code operates inside a doPrivileged() block. The reflected field may be a class (static) field or an instance field. The following example uses the GetValue method to retrieve the value of a static field. A Field provides information about, and dynamic access to, a single field of a class or an interface. The method is neither declared nor inherited by the class of obj.
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