Getting java run time memory statistics

   public static void logJVMStatistics()
    {
        System.out.println("JVM Statistics -- Max : " + Runtime.getRuntime().maxMemory() + "; " +
                            "Free: " + Runtime.getRuntime().freeMemory() + "; " +
                            "Total: " + Runtime.getRuntime().totalMemory());
    }

Iterate through values of Java Hashtable example

This example shows how to iterate over hash table using enumerator:

//create Hashtable object    
Hashtable ht = new Hashtable();    
//add key value pairs to Hashtable    
ht.put("1","One");    
ht.put("2","Two");    
ht.put("3","Three");
//get Enumeration of values contained in Hashtable using
//Enumeration elements() method of Hashtable class
Enumeration e = ht.elements();    
//iterate through Hashtable values Enumeration    
while(e.hasMoreElements())
      System.out.println(e.nextElement());

How do I convert String to Date object?

The following code shows how we can convert a string representation of date into java.util.Date object.
To convert a string of date we can use the help from java.text.SimpleDateFormat that extends java.text.DateFormat abstract class.







import java.text.DateFormat;

import java.text.SimpleDateFormat;

import java.text.ParseException;

import java.util.Date;




public Date StringToDate

{

         DateFormat df = new SimpleDateFormat("dd/MM/yyyy");




       try

        {

            Date today = df.parse("20/12/2005");           

           System.out.println("Today = " + df.format(today));

      } catch (ParseException e)

      {

            System.out.println("Cannot convert to date "+e);

        }

    

}

And here is the result of our code:

Today = 20/12/2005

The example starts by creating an instance of SimpleDateFormat with "dd/MM/yyyy" format which mean that the date string is formatted in day-month-year sequence.
Finally using the parse(String source) method we can get the Date instance. Because parse method can throw java.text.ParseException exception if the supplied date is not in a valid format; we need to catch it.
Here are the list of defined patterns that can be used to format the date taken from the Java class documentation.

Letter	Date / Time Component	Examples
G	Era designator	AD
y	Year	1996; 96
M	Month in year	July; Jul; 07
w	Week in year	27
W	Week in month	2
D	Day in year	189
d	Day in month	10
F	Day of week in month	2
E	Day in week	Tuesday; Tue
a	Am/pm marker	PM
H	Hour in day (0-23)	0
k	Hour in day (1-24)	24
K	Hour in am/pm (0-11)	0
h	Hour in am/pm (1-12)	12
m	Minute in hour	30
s	Second in minute	55
S	Millisecond	978
z	Time zone	Pacific Standard Time; PST; GMT-08:00
Z	Time zone	-0800