Free memory result should indicate whether Garbage collector has run : Garbage Collection « Java Source And Data Type « SCJP

1. SCJP
2. Java Source And Data Type
3. Garbage Collection

import java.util.Date;
   
   public class MainClass {
      public static void main(String [] args) {
         Runtime rt = Runtime.getRuntime();
         System.out.println("Total JVM memory: " + rt.totalMemory());
         System.out.println("Before Memory = " + rt.freeMemory());
         Date d = null;
         for(int i = 0;i<10000;i++) {
            d = new Date();
            d = null;
        }
        System.out.println("After Memory = " + rt.freeMemory());
        rt.gc();   // an alternate to System.gc()
        System.out.println("After GC Memory = " + rt.freeMemory());
     }
  }