/java-reflection

Primary LanguageJava

JAVA REFLECTION

  • Language and JVM feature that gives us Runtime access to information about our application's classes, and objects.
  • Those features are available to us through the java.lang.reflect (Reflection API) package.

getClass()

  • Returns the runtime class of an object.
  • The returned Class object is the object that is locked by static synchronized methods of the represented class.

Object Creation

  • class.getDeclaredConstructor()
    • Returns all the constructors declared by the class. (public, protected, default (package) access, and private constructors)
  • class.getConstructor()
    • Returns only the public constructors declared by the class.

Fields

  • Fields are variables that belong to a class or object.
  • class.getDeclaredFields()
    • Returns all the fields declared by the class. (public, protected, default (package) access, and private fields)
    • Includes inherited fields.
  • class.getFields()
    • Returns only the public fields declared by the class.
    • Includes inherited fields.
  • class.getDeclaredField(<field_name>)
    • Returns a specific field declared by the class.
    • Includes inherited fields.
    • Throws NoSuchFieldException if the field does not exist.

Synthetic Fields

  • Fields that are generated by the compiler for internal usage.
  • For example, the this keyword is a synthetic field.
  • field.isSynthetic()
    • Returns true if the field is synthetic.
  • field.isEnumConstant()
    • Returns true if the field is an enum constant.
  • field.setAccessible(true)
    • Allows us to access private fields.
    • if classes belong to different modules, that don't allow access to those class, we can use --add-opens to allow access to private fields.

Methods

  • Methods are functions that belong to a class or object.
  • getMethod() searches in order backwards through the class hierarchy.
  • getDeclaredMethods()
    • Returns all the methods declared by the class. (public, protected, default (package) access, and private methods)
    • Includes inherited methods.
  • getMethods()
    • Returns only the public methods declared by the class.
    • Includes inherited methods.
  • getDeclaredMethod(<method_name>, <parameter_types>)
    • Returns a specific method declared by the class.
    • Looks only at the methods in current class.
    • Throws NoSuchMethodException if the method does not exist.
  • getMethod(<method_name>, <parameter_types>)
    • Returns a specific public method declared by the class.
    • Includes inherited methods.
    • Throws NoSuchMethodException if the method does not exist.