Reflection API : Its a per-defined programming interface provided by JDK, which helps us to find out all the capabilities of a class at runtime.
POC of Reflection API:
Part 1 consists POC on
1. Reflection on Class
2. Reflections on Methods
3. Reflections on Fields.
Finding out the class information.
Lets create a simple class
with name CompanyClassInformation
package com.learning.reflections;
public class CompanyProfileInformation {
private String name;
private int age;
private String company;
public CompanyProfileInformation() {
System.out.println("Calling Constructor");
this.name = "bharani";
this.age = 26;
this.company = "EIL";
System.out.println(name);
System.out.println(age);
System.out.println(company);
}
public CompanyProfileInformation(String name, int age, String company) {
System.out.println("Calling Parameterized Constructor");
this.name = name;
this.age = age;
this.company = company;
System.out.println(this.name);
System.out.println(this.age);
System.out.println(this.company);
}
public void getName() {
System.out.println(this.name);
}
public void getAge() {
System.out.println(this.age);
}
public void getCompany() {
System.out.println(this.company);
}
public void getName(String name) {
System.out.println(name);
}
public void getAge(int age) {
System.out.println(age);
}
public void getCompany(String company) {
System.out.println(company);
}
}
Lets create one more Class called FindingOutClassInformation, Which tells us the information like Class Name,
Class Loaders, Constructors and Invoking default and paramterized constructor through reflections.
package com.learning.reflections;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
public class FindingOutClassInformation {
@SuppressWarnings({ "rawtypes", "unchecked" })
public static void main(String[] args) {
try {
Class companyProfileInformation = Class.forName("com.learning.reflections.CompanyProfileInformation");
// getName will provide you the Class Name with its Package
System.out.println(companyProfileInformation.getName());
// getName will provide you the Class Name without the package
System.out.println("*****************************");
System.out.println(companyProfileInformation.getSimpleName());
// getClassLoader will provide you the information about the
// ClassLoader which loads the class in the JVM.
System.out.println("*****************************");
System.out.println(companyProfileInformation.getClassLoader());
// provides you the information about Constructors
System.out.println("*****************************");
Constructor[] companyProfileInformationDeclaredConstructors = companyProfileInformation
.getDeclaredConstructors();
for (Constructor constructor : companyProfileInformationDeclaredConstructors) {
System.out.println(constructor.getName());
}
System.out.println("*****************************");
Constructor[] companyProfileInformationConstructors = companyProfileInformation.getConstructors();
for (Constructor constructor : companyProfileInformationConstructors) {
System.out.println(constructor.getName());
}
// Invoking a parameterized Constructor
Constructor companyProfileInformationParameterizedConstructor = companyProfileInformation
.getConstructor(String.class, int.class, String.class);
CompanyProfileInformation paramterizedobject = (CompanyProfileInformation) companyProfileInformationParameterizedConstructor
.newInstance("Bharani", 27, "EGIL");
System.out.println("*****************************");
// Invoking default Constructor
Constructor companyProfileInformationdefaultConstructor = companyProfileInformation.getConstructor();
CompanyProfileInformation defaultobject = (CompanyProfileInformation) companyProfileInformationdefaultConstructor
.newInstance();
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (NoSuchMethodException e) {
e.printStackTrace();
} catch (SecurityException e) {
e.printStackTrace();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (IllegalArgumentException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
}
}
}
output:
com.learning.reflections.CompanyProfileInformation
*****************************
CompanyProfileInformation
*****************************
sun.misc.Launcher$AppClassLoader@3301f287
*****************************
com.learning.reflections.CompanyProfileInformation
com.learning.reflections.CompanyProfileInformation
*****************************
com.learning.reflections.CompanyProfileInformation
com.learning.reflections.CompanyProfileInformation
Calling Parameterized Constructor
Bharani
27
EGIL
*****************************
Calling Constructor
bharani
26
EIL
Finding the information about the methods,declared Methods and invoking methods of a Class
Lets create one more Class with Name
FindingOutTheMethodsOftheClass which provides us the information of methods of CompanyClassInformation through Reflections.
package com.learning.reflections;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.List;
public class FindingOutTheMethodsOftheClass {
@SuppressWarnings({ "rawtypes", "unchecked" })
public static void main(String[] args) throws NoSuchMethodException, SecurityException, IllegalAccessException,
IllegalArgumentException, InvocationTargetException, InstantiationException {
try {
// This will create a Class Object
Class complayProfileInformation = Class.forName("com.learning.reflections.CompanyProfileInformation");
// getMethods will return you the methods used in your current class
// as well as its super class.
// ***************************************************************
// complayProfileInformation Super class is Object, so the methods
// of Object class is also visible.
Method[] methods = complayProfileInformation.getMethods();
for (Method m : methods) {
System.out.println(m.getName());
}
System.out.println("************************************************************************");
// getDeclaredMethods will return you the methods which are declared
// in the current class
Method[] declaredMethods = complayProfileInformation.getDeclaredMethods();
for (Method declaredm : declaredMethods) {
System.out.println(declaredm.getName());
}
System.out.println("************************************************************************");
CompanyProfileInformation cpi = (CompanyProfileInformation) complayProfileInformation.newInstance();
// Invoking Methods through Reflections.
List<String> listMethodName = new ArrayList<>();
listMethodName.add("getName");
listMethodName.add("getAge");
listMethodName.add("getCompany");
for (String methodname : listMethodName) {
switch (methodname) {
case "getName":
System.out.println("************************************************************************");
Method getNamewithParameters = complayProfileInformation.getDeclaredMethod(methodname);
getNamewithParameters.invoke(cpi);
Method getNameWithoutParameters = complayProfileInformation.getDeclaredMethod(methodname,
String.class);
getNameWithoutParameters.invoke(cpi, "Bharani Ravi Kanth R");
System.out.println("************************************************************************");
break;
case "getAge":
System.out.println("************************************************************************");
Method getagewithParameters = complayProfileInformation.getDeclaredMethod(methodname);
getagewithParameters.invoke(cpi);
Method getageWithoutParameters = complayProfileInformation.getDeclaredMethod(methodname, int.class);
getageWithoutParameters.invoke(cpi, 32);
System.out.println("************************************************************************");
break;
case "getCompany":
System.out.println("************************************************************************");
Method getCompanywithParameters = complayProfileInformation.getDeclaredMethod(methodname);
getCompanywithParameters.invoke(cpi);
Method getCompanyWithoutParameters = complayProfileInformation.getDeclaredMethod(methodname,
String.class);
getCompanyWithoutParameters.invoke(cpi, "BHARANIRAVIKANTHSOFT");
System.out.println("************************************************************************");
break;
default:
System.err.println("No Such Method available");
break;
}
}
} catch (ClassNotFoundException e) {
System.err.println(e.getMessage());
}
}
}
output:
getName
getName
getAge
getAge
getCompany
getCompany
wait
wait
wait
equals
toString
hashCode
getClass
notify
notifyAll
************************************************************************
getName
getName
getAge
getAge
getCompany
getCompany
************************************************************************
Calling Constructor
bharani
26
EIL
************************************************************************
bharani
Bharani Ravi Kanth R
************************************************************************
************************************************************************
26
32
************************************************************************
************************************************************************
EIL
BHARANIRAVIKANTHSOFT
************************************************************************
Accessing the Private variables of a class.
Lets create a simple class PrivateMembersClass.Java which has only private and public variables
package com.learning.reflections;
public class PrivateMembersClass {
private String empName = "bharani Ravi Kanth";
private int empAge = 27;
private String empCompany = "EIL";
public String mobileNo = "+918778888278";
public String designation = "Solution Integrator";
}
Create one more class FindingOutThePrivateAndPublicVariableOfaClass which we use to access the variables of PrivateMembersClass class through reflections.
package com.learning.reflections;
import java.lang.reflect.Field;
public class FindingOutThePrivateAndPublicVariableOfaClass {
@SuppressWarnings("rawtypes")
public static void main(String[] args)
throws ClassNotFoundException, IllegalArgumentException, IllegalAccessException, InstantiationException {
Class privateOutThePrivatePublicVariables = Class.forName("com.learning.reflections.PrivateMembersClass");
// GetFields will provide only the public Variables
Field[] variablesinClass = privateOutThePrivatePublicVariables.getFields();
for (Field field : variablesinClass) {
System.out.println(field.getName());
}
System.out.println("**********************************");
// GetDeclaredFields will provide you private and public Variables
Field[] PrivateandPublicvariablesinClass = privateOutThePrivatePublicVariables.getDeclaredFields();
for (Field field : PrivateandPublicvariablesinClass) {
System.out.println(field.getName());
}
System.out.println("**********************************");
// GetDeclaredFields accessing the public variables from the class
PrivateMembersClass membersClass = (PrivateMembersClass) privateOutThePrivatePublicVariables.newInstance();
for (Field field : variablesinClass) {
System.out.println(field.getName());
System.out.println(field.get(membersClass));
}
System.out.println("**********************************");
// GetDeclaredFields accessing the public and private variables from the
// class
// you cannot access private variables directly, We need to set the value as true for the
// Field method setAccessible
for (Field field : PrivateandPublicvariablesinClass) {
System.out.println(field.getName());
field.setAccessible(true);
System.out.println(field.get(membersClass));
}
}
}
Output:
mobileNo
designation
**********************************
empName
empAge
empCompany
mobileNo
designation
**********************************
mobileNo
+918778888278
designation
Solution Integrator
**********************************
empName
bharani Ravi Kanth
empAge
27
empCompany
EIL
mobileNo
+918778888278
designation
Solution Integrator
