How to Use garbage collection in java?

import java.util.*;

 class GarbageCollection{  

 public static void main(String s[]) throws Exception  

 {      Runtime rs =  Runtime.getRuntime();

  System.out.println("Free memory in JVM before Garbage Collection = "+rs.freeMemory()); 

     rs.gc();//garbage collection    

  System.out.println("Free memory in JVM after Garbage Collection = "+rs.freeMemory()); 

//We can also use 

System.gc();

  }}