Example of how to create class and access private constructor of the class using reflection and how to prevent it

Singleton.java

/**
 * @author hendrawd on 22/12/17
 */
public class Singleton {

    // some singleton creation mechanisms

    private Singleton(){
        // throwing an exception here is needed to avoid developer cheating by creating this class with reflection
        throw new UnsupportedOperationException("Should not create instance of Util class. Please use as static..");
    }

    public String getText(){
        return "Some text";
    }
}

SingletonCreator.java

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;

/**
 * @author hendrawd on 22/12/17
 */
public class SingletonCreator {

    public static void create() {
        Singleton singleton = null;
        // try {
        //     singleton = Singleton.class.newInstance();
        // } catch (InstantiationException e) {
        //     e.printStackTrace();
        // } catch (IllegalAccessException e) {
        //     e.printStackTrace();
        // }

        try {
            Constructor<Singleton> constructor = Singleton.class.getDeclaredConstructor();
            // Constructor<Singleton> constructor = (Constructor<Singleton>) Class.forName("package.name.SingletonCreator").getConstructor();
            constructor.setAccessible(true);
            singleton = constructor.newInstance();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        }
        System.out.println(singleton.getText());
    }
}