Javadoubts

Java Reflection

Java Reflection helps us to read or modify metadata related to class, fields, methods and constructors at run time.

It allow us to fetch or get metadata information like scope, modifier, name, parameters, method invocation etc. related to class, field, constructor and method.

java.lang.reflect package is having Field, Method, Constructor classes which provides us the capability to fetch or modify public as well as private metadata related to class, field, constructor and method.

isInterface(), getSuperclass(), getName(), getClass(), getMethods(), getFields(), .getConstructors() are some of the common and most used method from java.lang.Class class to get or fetch metadata.

Below are the steps to get or read metadata using reflection:

1. Get java.lang.Class class object
2. Using class object get or fetch class metadata at run time.

It require a java.lang.Class class object to get the metadata using reflection. Below are the methods allow us to get metadata using reflection:

1. forName() Method:

forName() static method from java.lang.Class class allow us to create or get Class object.

2. getClass() Method:

getClass() native final method from java.lang.Object class also allow us to get java.lang.Class class object.

3. Using .class

.class extension also allow us to get java.lang.Class class object as shown below:

Field metadata using Reflection

Below is an example to access class fields metadata such as field name, modifier, get or set value etc. using reflection.

OUTPUT:
firstName
lastName
age

Below is reflection example to access private field name from Student class.

OUTPUT
Name =John
Is Interface = false

Below is an example to set age field value of Student class using reflection:

OUTPUT
age = 0
age = 12

Method metadata using Reflection

Below is an example to access method metadata such as method name, parameters and its type, modifiers, method invocation using reflection.

OUTPUT:
Method: private void com.practice.core.Student.getStudentName(java.lang.String)
Declaring Class: com.practice.core.Student
Parameter Type: [Ljava.lang.Class;@246ae04d
Return Type: void

Below is an example to invoke method using Class.forName() method using reflection:

Constructor metadata using Reflection

Below is an example to access constructor and get its metadata such as constructor name, parameters and its type, modifiers using reflection.

OUTPUT

Reflection API disadvantages:

Below are some of the disadvantages of using the reflection API:

1. It makes system slow.
2. It can cause or end up with an unexpected error as class name binding happens at runtime.
3. It can be a security threat to an application as reflection allows us to access private as well as public fields and methods.