java calculate method run time

long startTime = System.currentTimeMillis();

doReallyLongThing(); // call your method here
long endTime = System.currentTimeMillis();
// calculate the difference - that the method just took to executeSystem.out.println("That took " + (endTime - startTime) + " milliseconds");

SQL basics- complete reference guide - part8 SQL System Commands

Part8: SQL System Commands Reference guide

ARRAY_GETReturns one element of an array.ARRAY_GET(arrayExpression, indexExpression)
ARRAY_LENGTHReturns the length of an array.ARRAY_GET(arrayExpression)
AUTOCOMMITReturns true if auto commit is switched on for this session.AUTOCOMMIT()
CANCEL_SESSIONCancels the currently executing statement of another session.CANCEL_SESSION(sessionInt)
CASEWHEN FunctionReturns 'a' if the boolean expression is true, otherwise 'b'.CASEWHEN(boolean, aValue, bValue)
CASTConverts a value to another data type.CAST(value AS dataType)
COALESCEReturns the first value that is not null.COALESCE(aValue, bValue [,...])
CONVERTConverts a value to another data type.CONVERT(value, dataType)
CURRVALReturns the current (last) value of the sequence, independent of the session.CURRVAL( [ schemaName, ] sequenceString )
CSVREADReturns the result set of reading the CSV (comma separated values) file.CSVREAD(fileNameString [, columnsString [, csvOptions ] ] )
CSVWRITEWrites a CSV (comma separated values).CSVWRITE ( fileNameString, queryString [, csvOptions [, lineSepString] ] )
DATABASEReturns the name of the database.DATABASE()
DATABASE_PATHReturns the directory of the database files and the database name, if it is file
FILE_READReturns the contents of a file.FILE_READ(fileNameString [,encodingString])
GREATESTReturns the largest value that is not NULL, or NULL if all values are NULL.GREATEST(aValue, bValue [,...])
IDENTITYReturns the last inserted identity value for this session.IDENTITY()
IFNULLReturns the value of 'a' if it is not null, otherwise 'b'.IFNULL(aValue, bValue)
LEASTReturns the smallest value that is not NULL, or NULL if all values are NULL.LEAST(aValue, bValue [,...])
LOCK_MODEReturns the current lock mode.LOCK_MODE()
LOCK_TIMEOUTReturns the lock timeout of the current session (in milliseconds).LOCK_TIMEOUT()
LINK_SCHEMACreates table links for all tables in a schema.LINK_SCHEMA(targetSchemaString, driverString, urlString,
userString, passwordString, sourceSchemaString)
MEMORY_FREEReturns the free memory in KB (where 1024 bytes is a KB).MEMORY_FREE()
MEMORY_USEDReturns the used memory in KB (where 1024 bytes is a KB).MEMORY_USED()
NEXTVALReturns the next value of the sequence.NEXTVAL ( [ schemaName, ] sequenceString )
NULLIFReturns NULL if 'a' is equals to 'b', otherwise 'a'.NULLIF(aValue, bValue)
READONLYReturns true if the database is read-only.READONLY()
ROWNUMReturns the number of the current row.ROWNUM()
SCHEMAReturns the name of the default  schema for this session.SCHEMA()
SCOPE_IDENTITYReturns the last inserted identity value for this session for the current scope.SCOPE_IDENTITY()
SESSION_IDReturns the unique session id number for the current database connection.SESSION_ID()
SETUpdates a variable with the given value.SET(@variableName, value)
TABLEReturns the result set.{ TABLE | TABLE_DISTINCT } ( { name dataType = expression } [,...] )
TRANSACTION_IDReturns the current transaction id for this session.TRANSACTION_ID()
USERReturns the name of the current user of this session.{ USER | CURRENT_USER } ()Select User();

SQL basics- complete reference guide - part7 - Date Time Functions

Part7: SQL Date Time Functions Reference

CURRENT_DATEReturns the current date.{ CURRENT_DATE [ () ] | CURDATE() | SYSDATE | TODAY }
CURRENT_TIMEReturns the current time.{ CURRENT_TIME [ () ] | CURTIME() }
CURRENT_TIMESTAMPReturns the current timestamp.{ CURRENT_TIMESTAMP [ ( [ int ] ) ] | NOW( [ int ] ) }
DATEADDAdds units to a timestamp.DATEADD(unitString, addInt, timestamp)
DATEDIFFReturns the the number of crossed unit boundaries between two timestamps.{ DATEDIFF | TIMESTAMPDIFF } (unitString, aTimestamp, bTimestamp)
DAYNAMEReturns the name of the day (in English).DAYNAME(date)
DAY_OF_MONTHReturns the day of the month (1-31).DAY_OF_MONTH(date)
DAY_OF_WEEKReturns the day of the week (1 means Sunday).DAY_OF_WEEK(date)
DAY_OF_YEARReturns the day of the year (1-366).DAY_OF_YEAR(date)
EXTRACTReturns a specific value from a timestamps.EXTRACT ( { YEAR | YY | MONTH | MM | DAY | DD | DAY_OF_YEAR
    FROM timestamp )
FORMATDATETIMEFormats a date, time or timestamp as a string.FORMATDATETIME ( timestamp, formatString
[ , localeString [ , timeZoneString ] ] )
HOURReturns the hour (0-23) from a timestamp.HOUR(timestamp)
MINUTEReturns the minute (0-59) from a timestamp.MINUTE(timestamp)
MONTHReturns the month (1-12) from a timestamp.MONTH(timestamp)
MONTHNAMEReturns the name of the month (in English).MONTHNAME(date)
PARSEDATETIMEParses a string and returns a timestamp.PARSEDATETIME(string, formatString
[, localeString [, timeZoneString]])
QUARTERReturns the quarter (1-4) from a timestamp.QUARTER(timestamp)
SECONDReturns the second (0-59) from a timestamp.SECOND(timestamp)
WEEKReturns the week (1-53) from a timestamp.WEEK(timestamp)
YEARReturns the year from a timestamp.YEAR(timestamp)

Java Capture/save image from swing Component eg : JFrame JPanel ..

Capture image from any swing Component and save to file.
Capture  :
BufferedImage image = new BufferedImage(component.getWidth(),
                                     component.getHeight(), BufferedImage.TYPE_INT_RGB);
// paints into image's Graphics
Save Image :

SQL basics- complete reference guide - part6 - String functions

Part6: SQL String Functions Complete Reference

ASCIIReturns the ASCII value of the first character in the string.ASCII(string)
BIT_LENGTHReturns the number of bits in a string.BIT_LENGTH(string)
LENGTHReturns the number of characters in a string.{ LENGTH | CHAR_LENGTH | CHARACTER_LENGTH } ( string )
OCTET_LENGTHReturns the number of bytes in a string.OCTET_LENGTH(string)
CHARReturns the character that represents the ASCII value.{ CHAR | CHR } ( int )
CONCATCombines strings.CONCAT(string, string [,...])
DIFFERENCEReturns the difference between the sounds of two strings.DIFFERENCE(string, string)
HEXTORAWConverts a hex representation of a string to a string.HEXTORAW(string)
RAWTOHEXConverts a string to the hex representation.RAWTOHEX(string)
INSTRReturns the location of a search string in a string.INSTR(string, searchString, [, startInt])
INSERT FunctionInserts a additional string into the original string at a specified start position.INSERT(originalString, startInt, lengthInt, addString)
LOWERConverts a string to lowercase.{ LOWER | LCASE } ( string )
UPPERConverts a string to uppercase.{ UPPER | UCASE } ( string )
LEFTReturns the leftmost number of characters.LEFT(string, int)
RIGHTReturns the rightmost number of characters.RIGHT(string, int)
LOCATEReturns the location of a search string in a string.LOCATE(searchString, string [, startInt])
POSITIONReturns the location of a search string in a string.POSITION(searchString, string)
LPADLeft pad the string to the specified length.LPAD(string, int[, paddingString])
RPADRight pad the string to the specified length.RPAD(string, int[, paddingString])
LTRIMRemoves all leading spaces from a string.LTRIM(string)
RTRIMRemoves all trailing spaces from a string.RTRIM(string)
TRIMRemoves all leading spaces, trailing spaces, or spaces at both ends, from a string.TRIM ( [ { LEADING | TRAILING | BOTH } [ string ] FROM ] string )
REGEXP_REPLACEReplaces each substring that matches a regular expression.REGEXP_REPLACE(inputString, regexString, replacementString)
REPEATReturns a string repeated some number of times.REPEAT(string, int)
REPLACEReplaces all occurrences of a search string in a text with another string.REPLACE(string, searchString [, replacementString])
SOUNDEXReturns a four character code representing the sound of a string.SOUNDEX(string)
SPACEReturns a string consisting of a number of spaces.SPACE(int)
STRINGDECODEConverts a encoded string using the Java string literal encoding format.STRINGDECODE(string)
STRINGENCODEEncodes special characters in a string using the Java string literal encoding format.STRINGENCODE(string)
STRINGTOUTF8Encodes a string to a byte array using the UTF8 encoding format.STRINGTOUTF8(string)
SUBSTRINGReturns a substring of a string starting at a position.{ SUBSTRING | SUBSTR } ( string, startInt [, lengthInt ] )
UTF8TOSTRINGDecodes a byte array in the UTF8 format to a string.UTF8TOSTRING(bytes)
XMLATTRCreates an XML attribute element of the form "name=value".XMLATTR(nameString, valueString)
XMLNODECreate an XML node element.XMLNODE(elementString [, attributesString [, contentString]])
XMLCOMMENTCreates an XML comment.XMLCOMMENT(commentString)
XMLCDATACreates an XML CDATA element.XMLCDATA(valueString)
XMLTEXTCreates an XML text element.XMLTEXT(valueString)

java pad string left right - String.format() method

String.format() can be used to left/right pad a given string.
public static String padRight(String s, int n) {
     return String.format("%1$-" + n + "s", s);  }
public static String padLeft(String s, int n) {
    return String.format("%1$#" + n + "s", s);  }
public static void main(String args[]) throws Exception {
 System.out.println(padRight("Howto", 20) + "*");
 System.out.println(padLeft("Howto", 25) + "*");

Top Java Interview Question : reverse a string using recursion

Best Answer using Recursion :

  public String reverse(String str) {
     if ((null == str) || (str.length()  <= 1)) {
        return str;
    return reverse(str.substring(1)) + str.charAt(0);

Less Best Answer :
public class JdkReverser implements Reverser {
  public String reverse(String str) {
     if ((null == str) || (str.length() <= 1)) {
         return str;
     return new StringBuffer(str).reverse().toString();

SQL basics- complete reference guide - part5 - Mathematical Functions

Part5: Mathematical Functions in SQL- Complete Reference

ABSABS ( { int | long | decimal | double } )
ATAN2ATAN2(double, double)
BITANDThe bitwise AND operation.BITAND(long, long)
BITORThe bitwise OR operation.BITOR(long, long)
BITXORThe bitwise XOR operation.BITXOR(long, long)
MODThe modulo operation.MOD(long, long)
POWERPOWER(double, double)
RANDCalling the function without parameter returns the next a pseudo random number.RAND( [ int ] )
RANDOM_UUIDReturns a new UUID with 122 pseudo random bits.RANDOM_UUID()
ROUNDRounds to a number of digits.ROUND(double, digitsInt)
ROUNDMAGICThis function rounds numbers in a good way, but it is slow.ROUNDMAGIC(double)
SECURE_RANDGenerates a number of cryptographically secure random numbers.SECURE_RAND(int)
SIGNReturns -1 if the value is smaller 0, 0 if zero, and otherwise 1.SIGN ( { int | long | decimal | double } )
ENCRYPTEncrypts data using a key.ENCRYPT(algorithmString, keyBytes, dataBytes)
DECRYPTDecrypts data using a key.DECRYPT(algorithmString, keyBytes, dataBytes)
HASHCalculate the hash value using an algorithm, and repeat this process for a number of iterations.HASH(algorithmString, dataBytes, iterationInt)
TRUNCATETruncates to a number of digits (to the next value closer to 0).TRUNCATE(double, digitsInt)
COMPRESSCompresses the data using the specified compression algorithm.COMPRESS(dataBytes [, algorithmString])
EXPANDExpands data that was compressed using the COMPRESS function.EXPAND(bytes)
ZEROReturns the value 0.ZERO()

SQL basics- complete reference guide - part4 - Aggregate Functions in SQL

Part4: Aggregate Functions in SQL- complete reference sheet

AVGThe average (mean) value.AVG ( [ DISTINCT ] { int | long | decimal | double } )
BOOL_ANDReturns true if all expressions are true.BOOL_AND(boolean)
BOOL_ORReturns true if any expression is true.BOOL_OR(boolean)
COUNTThe count of all row, or of the non-null values.COUNT( { * | { [ DISTINCT ] expression } } )
GROUP_CONCATConcatenates strings with a separator.GROUP_CONCAT ( [ DISTINCT ] string
[ ORDER BY { expression [ ASC | DESC ] } [,...] ]
[ SEPARATOR expression ] )
MAXThe highest value.MAX(value)
MINThe lowest value.MIN(value)
SUMThe sum of all values.SUM( [ DISTINCT ] { int | long | decimal | double } )
SELECTIVITYEstimates the selectivity (0-100) of a value.SELECTIVITY(value)
STDDEV_POPThe population standard deviation.STDDEV_POP( [ DISTINCT ] double )
STDDEV_SAMPThe sample standard deviation.STDDEV_SAMP( [ DISTINCT ] double )
VAR_POPThe population variance (square of the population standard deviation).VAR_POP( [ DISTINCT ] double )
VAR_SAMPThe sample variance (square of the sample standard deviation).VAR_SAMP( [ DISTINCT ] double )

Call one constructor from another in Java

Is this possible to call one constructor from another in Java ?

Yes, it is possible:

public class Foo
    private int x;

    public Foo()
        this(1);//calling constructor -->> public Foo(int x)

    public Foo(int x)
        this.x = x;