Returns the total number of fields of this class.ĩ) public Method getDeclaredMethods()throws SecurityException Loads the class and returns the reference of Class class.ģ) public Object newInstance()throws InstantiationException,IllegalAccessExceptionĨ) public Field getDeclaredFields()throws SecurityException Caching normally consists of creating a Map between class names to Class objects, as well as method/field names to Method or Field objects respectively.Commonly used methods of Class class: MethodĢ) public static Class forName(String className)throws ClassNotFoundException Private constructors can be accessed by using tAccessible(true) as you would expect Appendix B: Caching Reflectionīecause reflection is incredibly performance heavy (due to the overhead created by using reflection), it is often a good idea to cache reflection so access to the same methods/fields are quicker. InstantiationException if it fails to instantiate the class.
NoSuchMethodException for when it cannot find the specific constructor.
#JAVA REFLECTION TUTORIAL FOR BEGINNERS CODE#
Import // Code here public void someMethod () throws InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException, NoSuchMethodException Thrown when setting the value of a field or invoking a methodĬonstructors in reflection are almost identical to using methods via reflection. The common ones are outlined below: Exception Otherwise, you need to supply an instance of the class which has that method.
In the example below, you are able to retrieve the String object from a different class ExternalClass.java (You can view this file by pressing the file icon on the left). Reflection can be used to access private fields from external classes that you would not normally have access to. Most tutorials would probably tell you why reflection is very bad practice and that it should almost never be used under any circumstances, but this tutorial won’t inform you of the cons of reflection - that’s for you to discover. This allows a plethora of features that could never be accomplished without reflection, such as reading annotations that are attached to methods and running code that are not normally accessible. In the context of Java, this means that we can write code in Java to modify how code runs in Java, whilst it is running. Reflection basically allows you to write code in a particular language that can manipulate and analyse code written in the same language at runtime.