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

TOPIC	TEXT	SYNTAX	Example
ARRAY_GET	Returns one element of an array.	ARRAY_GET(arrayExpression, indexExpression)
ARRAY_LENGTH	Returns the length of an array.	ARRAY_GET(arrayExpression)
AUTOCOMMIT	Returns true if auto commit is switched on for this session.	AUTOCOMMIT()
CANCEL_SESSION	Cancels the currently executing statement of another session.	CANCEL_SESSION(sessionInt)
CASEWHEN Function	Returns 'a' if the boolean expression is true, otherwise 'b'.	CASEWHEN(boolean, aValue, bValue)
CAST	Converts a value to another data type.	CAST(value AS dataType)
COALESCE	Returns the first value that is not null.	COALESCE(aValue, bValue [,...])
CONVERT	Converts a value to another data type.	CONVERT(value, dataType)
CURRVAL	Returns the current (last) value of the sequence, independent of the session.	CURRVAL( [ schemaName, ] sequenceString )
CSVREAD	Returns the result set of reading the CSV (comma separated values) file.	CSVREAD(fileNameString [, columnsString [, csvOptions ] ] )
CSVWRITE	Writes a CSV (comma separated values).	CSVWRITE ( fileNameString, queryString [, csvOptions [, lineSepString] ] )
DATABASE	Returns the name of the database.	DATABASE()
DATABASE_PATH	Returns the directory of the database files and the database name, if it is file based.	DATABASE_PATH()
FILE_READ	Returns the contents of a file.	FILE_READ(fileNameString [,encodingString])
GREATEST	Returns the largest value that is not NULL, or NULL if all values are NULL.	GREATEST(aValue, bValue [,...])
IDENTITY	Returns the last inserted identity value for this session.	IDENTITY()
IFNULL	Returns the value of 'a' if it is not null, otherwise 'b'.	IFNULL(aValue, bValue)
LEAST	Returns the smallest value that is not NULL, or NULL if all values are NULL.	LEAST(aValue, bValue [,...])
LOCK_MODE	Returns the current lock mode.	LOCK_MODE()
LOCK_TIMEOUT	Returns the lock timeout of the current session (in milliseconds).	LOCK_TIMEOUT()
LINK_SCHEMA	Creates table links for all tables in a schema.	LINK_SCHEMA(targetSchemaString, driverString, urlString, userString, passwordString, sourceSchemaString)
MEMORY_FREE	Returns the free memory in KB (where 1024 bytes is a KB).	MEMORY_FREE()
MEMORY_USED	Returns the used memory in KB (where 1024 bytes is a KB).	MEMORY_USED()
NEXTVAL	Returns the next value of the sequence.	NEXTVAL ( [ schemaName, ] sequenceString )
NULLIF	Returns NULL if 'a' is equals to 'b', otherwise 'a'.	NULLIF(aValue, bValue)
READONLY	Returns true if the database is read-only.	READONLY()
ROWNUM	Returns the number of the current row.	ROWNUM()
SCHEMA	Returns the name of the default  schema for this session.	SCHEMA()
SCOPE_IDENTITY	Returns the last inserted identity value for this session for the current scope.	SCOPE_IDENTITY()
SESSION_ID	Returns the unique session id number for the current database connection.	SESSION_ID()
SET	Updates a variable with the given value.	SET(@variableName, value)
TABLE	Returns the result set.	{ TABLE | TABLE_DISTINCT } ( { name dataType = expression } [,...] )
TRANSACTION_ID	Returns the current transaction id for this session.	TRANSACTION_ID()
USER	Returns 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

TOPIC	TEXT	SYNTAX	Example
CURRENT_DATE	Returns the current date.	{ CURRENT_DATE [ () ] | CURDATE() | SYSDATE | TODAY }
CURRENT_TIME	Returns the current time.	{ CURRENT_TIME [ () ] | CURTIME() }
CURRENT_TIMESTAMP	Returns the current timestamp.	{ CURRENT_TIMESTAMP [ ( [ int ] ) ] | NOW( [ int ] ) }
DATEADD	Adds units to a timestamp.	DATEADD(unitString, addInt, timestamp)
DATEDIFF	Returns the the number of crossed unit boundaries between two timestamps.	{ DATEDIFF | TIMESTAMPDIFF } (unitString, aTimestamp, bTimestamp)
DAYNAME	Returns the name of the day (in English).	DAYNAME(date)
DAY_OF_MONTH	Returns the day of the month (1-31).	DAY_OF_MONTH(date)
DAY_OF_WEEK	Returns the day of the week (1 means Sunday).	DAY_OF_WEEK(date)
DAY_OF_YEAR	Returns the day of the year (1-366).	DAY_OF_YEAR(date)
EXTRACT	Returns a specific value from a timestamps.	EXTRACT ( { YEAR | YY | MONTH | MM | DAY | DD | DAY_OF_YEAR     | DOY | HOUR | HH | MINUTE | MI | SECOND | SS | MILLISECOND | MS }     FROM timestamp )
FORMATDATETIME	Formats a date, time or timestamp as a string.	FORMATDATETIME ( timestamp, formatString [ , localeString [ , timeZoneString ] ] )
HOUR	Returns the hour (0-23) from a timestamp.	HOUR(timestamp)
MINUTE	Returns the minute (0-59) from a timestamp.	MINUTE(timestamp)
MONTH	Returns the month (1-12) from a timestamp.	MONTH(timestamp)
MONTHNAME	Returns the name of the month (in English).	MONTHNAME(date)
PARSEDATETIME	Parses a string and returns a timestamp.	PARSEDATETIME(string, formatString [, localeString [, timeZoneString]])
QUARTER	Returns the quarter (1-4) from a timestamp.	QUARTER(timestamp)
SECOND	Returns the second (0-59) from a timestamp.	SECOND(timestamp)
WEEK	Returns the week (1-53) from a timestamp.	WEEK(timestamp)
YEAR	Returns 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
component.paint(image.getGraphics());

Save Image :

SQL basics- complete reference guide - part6 - String functions

Part6: SQL String Functions Complete Reference

TOPIC	TEXT	SYNTAX	Example
ASCII	Returns the ASCII value of the first character in the string.	ASCII(string)
BIT_LENGTH	Returns the number of bits in a string.	BIT_LENGTH(string)
LENGTH	Returns the number of characters in a string.	{ LENGTH | CHAR_LENGTH | CHARACTER_LENGTH } ( string )
OCTET_LENGTH	Returns the number of bytes in a string.	OCTET_LENGTH(string)
CHAR	Returns the character that represents the ASCII value.	{ CHAR | CHR } ( int )
CONCAT	Combines strings.	CONCAT(string, string [,...])
DIFFERENCE	Returns the difference between the sounds of two strings.	DIFFERENCE(string, string)
HEXTORAW	Converts a hex representation of a string to a string.	HEXTORAW(string)
RAWTOHEX	Converts a string to the hex representation.	RAWTOHEX(string)
INSTR	Returns the location of a search string in a string.	INSTR(string, searchString, [, startInt])
INSERT Function	Inserts a additional string into the original string at a specified start position.	INSERT(originalString, startInt, lengthInt, addString)
LOWER	Converts a string to lowercase.	{ LOWER | LCASE } ( string )
UPPER	Converts a string to uppercase.	{ UPPER | UCASE } ( string )
LEFT	Returns the leftmost number of characters.	LEFT(string, int)
RIGHT	Returns the rightmost number of characters.	RIGHT(string, int)
LOCATE	Returns the location of a search string in a string.	LOCATE(searchString, string [, startInt])
POSITION	Returns the location of a search string in a string.	POSITION(searchString, string)
LPAD	Left pad the string to the specified length.	LPAD(string, int[, paddingString])
RPAD	Right pad the string to the specified length.	RPAD(string, int[, paddingString])
LTRIM	Removes all leading spaces from a string.	LTRIM(string)
RTRIM	Removes all trailing spaces from a string.	RTRIM(string)
TRIM	Removes all leading spaces, trailing spaces, or spaces at both ends, from a string.	TRIM ( [ { LEADING | TRAILING | BOTH } [ string ] FROM ] string )
REGEXP_REPLACE	Replaces each substring that matches a regular expression.	REGEXP_REPLACE(inputString, regexString, replacementString)
REPEAT	Returns a string repeated some number of times.	REPEAT(string, int)
REPLACE	Replaces all occurrences of a search string in a text with another string.	REPLACE(string, searchString [, replacementString])
SOUNDEX	Returns a four character code representing the sound of a string.	SOUNDEX(string)
SPACE	Returns a string consisting of a number of spaces.	SPACE(int)
STRINGDECODE	Converts a encoded string using the Java string literal encoding format.	STRINGDECODE(string)
STRINGENCODE	Encodes special characters in a string using the Java string literal encoding format.	STRINGENCODE(string)
STRINGTOUTF8	Encodes a string to a byte array using the UTF8 encoding format.	STRINGTOUTF8(string)
SUBSTRING	Returns a substring of a string starting at a position.	{ SUBSTRING | SUBSTR } ( string, startInt [, lengthInt ] )
UTF8TOSTRING	Decodes a byte array in the UTF8 format to a string.	UTF8TOSTRING(bytes)
XMLATTR	Creates an XML attribute element of the form "name=value".	XMLATTR(nameString, valueString)
XMLNODE	Create an XML node element.	XMLNODE(elementString [, attributesString [, contentString]])
XMLCOMMENT	Creates an XML comment.	XMLCOMMENT(commentString)
XMLCDATA	Creates an XML CDATA element.	XMLCDATA(valueString)
XMLSTARTDOC	The string "	XMLSTARTDOC()
XMLTEXT	Creates 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

Function	Description	SYNTAX	Example
ABS	Returns the absolute value of a number.	ABS ( { int | long | decimal | double } )	SELECT ABS(-10) returns 10
ACOS	Returns the arc cosine of a value in radians.	ACOS(double)	SELECT ACOS(0.5) returns 1.0472...
ASIN	Returns the arc sine of a value in radians.	ASIN(double)	SELECT ASIN(0.5) returns 0.5236...
ATAN	Returns the arc tangent of a value in radians.	ATAN(double)	SELECT ATAN(1) returns 0.7854...
COS	Returns the cosine of an angle (radians).	COS(double)	SELECT COS(0) returns 1.0
COT	Returns the cotangent of an angle (radians).	COT(double)	SELECT COT(1) returns 0.6421...
SIN	Returns the sine of an angle (radians).	SIN(double)	SELECT SIN(0) returns 0.0
TAN	Returns the tangent of an angle (radians).	TAN(double)	SELECT TAN(0) returns 0.0
ATAN2	Returns the arc tangent of y/x, using the signs to determine the quadrant.	ATAN2(double, double)	SELECT ATAN2(1, 0) returns 1.5708...
BITAND	The bitwise AND operation.	BITAND(long, long)	SELECT BITAND(5, 3) returns 1
BITOR	The bitwise OR operation.	BITOR(long, long)	SELECT BITOR(5, 3) returns 7
BITXOR	The bitwise XOR operation.	BITXOR(long, long)	SELECT BITXOR(5, 3) returns 6
MOD	The modulo operation.	MOD(long, long)	SELECT MOD(7, 3) returns 1
CEILING	Returns the smallest integer >= the argument.	CEILING(double)	SELECT CEILING(2.3) returns 3
DEGREES	Converts radians to degrees.	DEGREES(double)	SELECT DEGREES(PI()) returns 180
EXP	Returns e raised to the power of the argument.	EXP(double)	SELECT EXP(1) returns 2.718...
FLOOR	Returns the largest integer <= the argument.	FLOOR(double)	SELECT FLOOR(2.7) returns 2
LOG	Returns the natural logarithm (base e).	LOG(double)	SELECT LOG(1) returns 0.0
LOG10	Returns the base‑10 logarithm.	LOG10(double)	SELECT LOG10(100) returns 2.0
RADIANS	Converts degrees to radians.	RADIANS(double)	SELECT RADIANS(180) returns 3.14159...
SQRT	Returns the square root.	SQRT(double)	SELECT SQRT(9) returns 3.0
PI	Returns the mathematical constant π.	PI()	SELECT PI() returns 3.14159...
POWER	Raises the first argument to the power of the second.	POWER(double, double)	SELECT POWER(2, 3) returns 8.0
RAND	Calling the function without parameter returns the next a pseudo random number. With a seed, the sequence becomes deterministic.	RAND( [ int ] )	SELECT RAND() returns 0.730...
RANDOM_UUID	Returns a new UUID with 122 pseudo random bits.	RANDOM_UUID()	SELECT RANDOM_UUID() returns 'a0eebc99-9c...'
ROUND	Rounds to a number of digits. Positive digits round to decimal places, negative to powers of ten.	ROUND(double, digitsInt)	SELECT ROUND(2.345, 2) returns 2.35
ROUNDMAGIC	This function rounds numbers in a good way, but it is slow. Uses a more mathematically correct rounding algorithm (half‑even).	ROUNDMAGIC(double)	SELECT ROUNDMAGIC(2.5) returns 2 (half-even)
SECURE_RAND	Generates an array of cryptographically secure random bytes. The argument specifies the number of bytes.	SECURE_RAND(int)	SELECT SECURE_RAND(8) returns [B@1a2b3c...
SIGN	Returns -1 if the value is smaller 0, 0 if zero, and otherwise 1.	SIGN ( { int | long | decimal | double } )	SELECT SIGN(-45) returns -1
ENCRYPT	Encrypts data using a key. The algorithm string can be 'AES', 'DES', etc.	ENCRYPT(algorithmString, keyBytes, dataBytes)	SELECT ENCRYPT('AES', '0123456789abcdef', 'my data')
DECRYPT	Decrypts data using a key. Must match the encryption algorithm and key.	DECRYPT(algorithmString, keyBytes, dataBytes)	SELECT DECRYPT('AES', '0123456789abcdef', encrypted_bytes)
HASH	Calculate the hash value using an algorithm, and repeat this process for a number of iterations. Useful for key derivation.	HASH(algorithmString, dataBytes, iterationInt)	SELECT HASH('SHA256', 'hello', 1000)
TRUNCATE	Truncates to a number of digits (to the next value closer to 0).	TRUNCATE(double, digitsInt)	SELECT TRUNCATE(2.345, 2) returns 2.34
COMPRESS	Compresses the data using the specified compression algorithm. If algorithm is omitted, default is 'LZF'.	COMPRESS(dataBytes [, algorithmString])	SELECT COMPRESS('Hello world', 'LZF')
EXPAND	Expands data that was compressed using the COMPRESS function.	EXPAND(bytes)	SELECT EXPAND(compressed_bytes)
ZERO	Returns the value 0. Useful as a placeholder when a constant zero is needed.	ZERO()	SELECT ZERO() returns 0

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

Part4: Aggregate Functions in SQL- complete reference sheet

Command/Function	Description	SYNTAX	Example
AVG	The average (mean) value.	AVG ( [ DISTINCT ] { int | long | decimal | double } )
BOOL_AND	Returns true if all expressions are true.	BOOL_AND(boolean)
BOOL_OR	Returns true if any expression is true.	BOOL_OR(boolean)
COUNT	The count of all row, or of the non-null values.	COUNT( { * | { [ DISTINCT ] expression } } )
GROUP_CONCAT	Concatenates strings with a separator.	GROUP_CONCAT ( [ DISTINCT ] string [ ORDER BY { expression [ ASC | DESC ] } [,...] ] [ SEPARATOR expression ] )
MAX	The highest value.	MAX(value)
MIN	The lowest value.	MIN(value)
SUM	The sum of all values.	SUM( [ DISTINCT ] { int | long | decimal | double } )
SELECTIVITY	Estimates the selectivity (0-100) of a value.	SELECTIVITY(value)
STDDEV_POP	The population standard deviation.	STDDEV_POP( [ DISTINCT ] double )
STDDEV_SAMP	The sample standard deviation.	STDDEV_SAMP( [ DISTINCT ] double )
VAR_POP	The population variance (square of the population standard deviation).	VAR_POP( [ DISTINCT ] double )
VAR_SAMP	The 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;
    }
}