JAVA EE: How to get the Constructors, methods, and variables of the class using Java Reflection

Tuesday, 14 November 2017

How to get the Constructors, methods, and variables of the class using Java Reflection

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How to get the Constructors, methods, and variables of the class using Java Reflection

Student.java

class Student
{
    public String name;
    public int age;
    private String gender;

    public Student()
    {

    }

    private Student(String name, int age)
    {
        super();
        this.name = name;
        this.age = age;
    }

    public void displayHello()
    {
        System.out.println("Hello");
    }
    
    
    private void displayWelcome()
    {
        System.out.println("Welcome");
    }

}

ReflectionDemo1.java

public class ReflectionDemo1
{
    public static void main(String[] args)
    {
        try
        {
            /*
             * forName method takes fully qualified name of classes or interface
             * as its argument and returns instance of the class assocaited with
             * it.
             */
            Class<?> classObj = Class.forName("Student");
            System.out.println(classObj.getName());
        }
        catch (ClassNotFoundException e)
        {
            e.printStackTrace();
        }

    }

}

Output

Student

ReflectionDemo2.java

import java.lang.reflect.Constructor;

public class ReflectionDemo2
{
    public static void main(String[] args)
    {

        try
        {
            Class<?> classObj = Class.forName("Student");

            /*
             * getConstructors() method returns array of Constructors object
             * that represent all the public constructors of the invoking
             * object. Remember, this method only returns public constructors.
             */
            Constructor<?>[] ct = classObj.getConstructors();
            for (int i = 0; i < ct.length; i++)
            {
                System.out.println(ct[i]);
            }

            System.out.println("--------------------------------------");

            /*
             * If you want to see all the declared constructors of a class then
             * use getDeclaredConstructors()
             */
            Constructor<?>[] cdt = classObj.getDeclaredConstructors();
            for (int i = 0; i < cdt.length; i++)
            {
                System.out.println(cdt[i]);
            }
        }
        catch (ClassNotFoundException e)
        {
            e.printStackTrace();
        }
    }
}

Output

public Student()
--------------------------------------
public Student()
private Student(java.lang.String,int)

ReflectionDemo3.java

import java.lang.reflect.Method;

public class ReflectionDemo3
{
    public static void main(String[] args)
    {
        try
        {
            Class<?> classObj = Class.forName("Student");

            /*
             * getMethods() method returns array of Method object that reflect
             * all the public method of invoking object.
             */
            Method[] methodArray = classObj.getMethods();
            for (int i = 0; i < methodArray.length; i++)
            {
                System.out.println(methodArray[i]);
            }

            System.out.println("---------------------------------");

            /*
             * getDeclaredMethods() returns only the declared methods of the
             * invoking class object.
             */
            Method[] declaredMethodArray = classObj.getDeclaredMethods();
            for (Method method : declaredMethodArray)
            {
                System.out.println(method);
            }
        }
        catch (ClassNotFoundException e)
        {
            e.printStackTrace();
        }
    }
}

Output

public void Student.displayHello()
public final void java.lang.Object.wait() throws java.lang.InterruptedException
public final void java.lang.Object.wait(long,int) throws java.lang.InterruptedException
public final native void java.lang.Object.wait(long) throws java.lang.InterruptedException
public boolean java.lang.Object.equals(java.lang.Object)
public java.lang.String java.lang.Object.toString()
public native int java.lang.Object.hashCode()
public final native java.lang.Class java.lang.Object.getClass()
public final native void java.lang.Object.notify()
public final native void java.lang.Object.notifyAll()
---------------------------------
public void Student.displayHello()
private void Student.displayWelcome()

ReflectionDemo4.java

import java.lang.reflect.Field;

public class ReflectionDemo4
{
    public static void main(String[] args)
    {
        try
        {
            Class<?> classObj = Class.forName("Student");

            /*
             * getFields() returns an array containing Field objects reflecting
             * all the accessible public members of the class or interface
             * represented by this Class object.
             */
            Field[] fieldArray = classObj.getFields();
            for (Field field : fieldArray)
            {
                System.out.println(field);
            }

            System.out.println("-------------------------------");

            /*
             * getDeclaredFields() returns array of Field objects reflecting all
             * the fields declared by the class or interface represented by this
             * Class object.
             */
            Field[] declaredFieldArray = classObj.getDeclaredFields();
            for (Field field : declaredFieldArray)
            {
                System.out.println(field);
            }

        }
        catch (ClassNotFoundException e)
        {
            e.printStackTrace();
        }
    }
}

Output

public java.lang.String Student.name
public int Student.age
-------------------------------
public java.lang.String Student.name
public int Student.age
private java.lang.String Student.gender