Confused in Reflection API concepts in JAVA [duplicate]

This question already has an answer here:

• What is reflection and why is it useful? 16 answers

I have just started learning Java. Sorry for asking silly doubts.

First of all, what is the use of Reflection API? I heard if we have same method and variable name then we use reflection API. I am confused.

Below program 1 and program 2 brings the same output. Then why do we use that. Kindly explain program 1 line 9 and 10. Thanks for the support friends.

Program 1:

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class Practice {

    public static void main(String[] args) throws NoSuchMethodException, SecurityException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
        String x="SampleTest";
    //Explain below 2 lines please
        Method method=Practice.class.getMethod(x, String.class);
        method.invoke(method, "Hello");


    }

    public static void SampleTest(String x){
        System.out.println("In Sample Test--"+x);

    }

}

Program 2:

public class Practice {

    public static void main(String[] args){
        String x="SampleTest";

        SampleTest("Hello");


    }

    public static void SampleTest(String x){
        System.out.println("In Sample Test--"+x);

    }

}

Output for both the program is In Sample Test--Hello

Thanks once again