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		ABS ( { int | long | decimal | double } )
ACOS		ACOS(double)
ASIN		ASIN(double)
ATAN		ATAN(double)
COS		COS(double)
COT		COT(double)
SIN		SIN(double)
TAN		TAN(double)
ATAN2		ATAN2(double, double)
BITAND	The bitwise AND operation.	BITAND(long, long)
BITOR	The bitwise OR operation.	BITOR(long, long)
BITXOR	The bitwise XOR operation.	BITXOR(long, long)
MOD	The modulo operation.	MOD(long, long)
CEILING		CEILING(double)
DEGREES		DEGREES(double)
EXP		EXP(double)
FLOOR		FLOOR(double)
LOG		LOG(double)
LOG10		LOG10(double)
RADIANS		RADIANS(double)
SQRT		SQRT(double)
PI		PI()
POWER		POWER(double, double)
RAND	Calling the function without parameter returns the next a pseudo random number.	RAND( [ int ] )
RANDOM_UUID	Returns a new UUID with 122 pseudo random bits.	RANDOM_UUID()
ROUND	Rounds to a number of digits.	ROUND(double, digitsInt)
ROUNDMAGIC	This function rounds numbers in a good way, but it is slow.	ROUNDMAGIC(double)
SECURE_RAND	Generates a number of cryptographically secure random numbers.	SECURE_RAND(int)
SIGN	Returns -1 if the value is smaller 0, 0 if zero, and otherwise 1.	SIGN ( { int | long | decimal | double } )
ENCRYPT	Encrypts data using a key.	ENCRYPT(algorithmString, keyBytes, dataBytes)
DECRYPT	Decrypts data using a key.	DECRYPT(algorithmString, keyBytes, dataBytes)
HASH	Calculate the hash value using an algorithm, and repeat this process for a number of iterations.	HASH(algorithmString, dataBytes, iterationInt)
TRUNCATE	Truncates to a number of digits (to the next value closer to 0).	TRUNCATE(double, digitsInt)
COMPRESS	Compresses the data using the specified compression algorithm.	COMPRESS(dataBytes [, algorithmString])
EXPAND	Expands data that was compressed using the COMPRESS function.	EXPAND(bytes)
ZERO	Returns the value 0.	ZERO()

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;
    }
}

SQL basics- complete reference guide - part3 - Data Types in SQL

Part3: SQL Data Types Reference

TOPIC	TEXT	SYNTAX	Example
INT Type	Possible values: -2147483648 to 2147483647.	INT | INTEGER | MEDIUMINT | INT4 | SIGNED
BOOLEAN Type	Possible values: TRUE and FALSE.	BOOLEAN | BIT | BOOL
TINYINT Type	Possible values are: -128 to 127.	TINYINT
SMALLINT Type	Possible values: -32768 to 32767.	SMALLINT | INT2 | YEAR
BIGINT Type	Possible values: -9223372036854775808 to 9223372036854775807.	BIGINT | INT8
IDENTITY Type	Auto-Increment value.	IDENTITY
DECIMAL Type	Data type with fixed precision and scale.	{ DECIMAL | NUMBER | DEC | NUMERIC } ( precisionInt [ , scaleInt ] )
DOUBLE Type	Floating point number.	{ DOUBLE [ PRECISION ] | FLOAT | FLOAT4 | FLOAT8 }
REAL Type	Single precision floating point number.	REAL
TIME Type	The format is hh:mm:ss.	TIME
DATE Type	The format is yyyy-MM-dd.	DATE
TIMESTAMP Type	The format is yyyy-MM-dd hh:mm:ss[.	{ TIMESTAMP | DATETIME | SMALLDATETIME }
BINARY Type	Represents a byte array.	{ BINARY | VARBINARY | LONGVARBINARY | RAW | BYTEA } [ ( precisionInt ) ]
OTHER Type	This type allows storing serialized Java objects.	OTHER
VARCHAR Type	Unicode String.	{ VARCHAR | LONGVARCHAR | VARCHAR2 | NVARCHAR     | NVARCHAR2 | VARCHAR_CASESENSITIVE}  [ ( precisionInt ) ]
VARCHAR_IGNORECASE Type	Same as VARCHAR, but not case sensitive when comparing.	VARCHAR_IGNORECASE [ ( precisionInt ) ]
CHAR Type	This type is supported for compatibility with other databases and older applications.	{ CHAR | CHARACTER | NCHAR } [ ( precisionInt ) ]
BLOB Type	Like BINARY, but intended for very large values such as files or images.	{ BLOB | TINYBLOB | MEDIUMBLOB | LONGBLOB | IMAGE | OID } [ ( precisionInt ) ]
CLOB Type	CLOB is like VARCHAR, but intended for very large values.	{ CLOB | TINYTEXT | TEXT | MEDIUMTEXT | LONGTEXT | NTEXT | NCLOB } [ ( precisionInt ) ]
UUID Type	Universally unique identifier.	UUID
ARRAY Type	An array of values.	ARRAY

SQL basics- complete reference guide - part2 - DDL

Part2: DDL -Data Definition Language Reference

Command	Description	SYNTAX	Example
ALTER INDEX RENAME	Renames an index.	ALTER INDEX indexName RENAME TO newIndexName
ALTER SCHEMA RENAME	Renames a schema.	ALTER SCHEMA schema RENAME TO newSchemaName
ALTER SEQUENCE	Changes the next value and the increment of a sequence.	ALTER SEQUENCE sequenceName [ RESTART WITH long ] [ INCREMENT BY long ]
ALTER TABLE ADD	Adds a new column to a table.	ALTER TABLE tableName ADD name dataType [ DEFAULT expression ] [ [ NOT ] NULL ] [ AUTO_INCREMENT | IDENTITY ] [ BEFORE columnName ]
ALTER TABLE ADD CONSTRAINT	Adds a constraint to a table.	ALTER TABLE tableName ADD constraint [ CHECK | NOCHECK ]
ALTER TABLE ALTER	Changes the data type of a column, rename a column, change the identity value, or change the selectivity.	ALTER TABLE tableName ALTER COLUMN columnName { { dataType [ DEFAULT expression ] [ [ NOT ] NULL ] [ AUTO_INCREMENT | IDENTITY ] }     | { RENAME TO name }     | { RESTART WITH long }     | { SELECTIVITY int }     | { SET DEFAULT expression }     | { SET NULL }     | { SET NOT NULL } }
ALTER TABLE DROP COLUMN	Removes a column from a table.	ALTER TABLE tableName DROP COLUMN columnName
ALTER TABLE DROP CONSTRAINT	Removes a constraint or a primary key from a table.	ALTER TABLE tableName DROP { CONSTRAINT [ IF EXISTS ] constraintName | PRIMARY KEY }
ALTER TABLE SET	Disables or enables referential integrity checking for a table.	ALTER TABLE tableName SET REFERENTIAL_INTEGRITY     { FALSE | TRUE [ CHECK | NOCHECK ] }
ALTER TABLE RENAME	Renames a table.	ALTER TABLE tableName RENAME TO newName
ALTER USER ADMIN	Switches the admin flag of a user on or off.	ALTER USER userName ADMIN { TRUE | FALSE }
ALTER USER RENAME	Renames a user.	ALTER USER userName RENAME TO newUserName
ALTER USER SET PASSWORD	Changes the password of a user.	ALTER USER userName SET { PASSWORD string | SALT bytes HASH bytes }
ALTER VIEW	Recompiles a view after the underlying tables have been changed or created.	ALTER VIEW viewName RECOMPILE
ANALYZE	Updates the selectivity statistics of all tables.	ANALYZE [ SAMPLE_SIZE rowCountInt ]
COMMENT	Sets the comment of a database object.	COMMENT ON { { COLUMN [ schemaName. ] tableName.columnName }     | { { TABLE | VIEW | CONSTANT | CONSTRAINT | ALIAS | INDEX | ROLE     | SCHEMA | SEQUENCE | TRIGGER | USER | DOMAIN } [ schemaName. ] objectName } } IS expression
CREATE AGGREGATE	Creates a new user-defined aggregate function.	CREATE AGGREGATE [ IF NOT EXISTS ] newAggregateName FOR className
CREATE ALIAS	Creates a new function alias.	CREATE ALIAS [ IF NOT EXISTS ] newFunctionAliasName [ DETERMINISTIC ] { FOR classAndMethodName | AS sourceCodeString }
CREATE CONSTANT	Creates a new constant.	CREATE CONSTANT [ IF NOT EXISTS ] newConstantName VALUE expression
CREATE DOMAIN	Creates a new data type (domain).	CREATE DOMAIN [ IF NOT EXISTS ] newDomainName AS dataType [ DEFAULT expression ] [ [ NOT ] NULL ] [ SELECTIVITY selectivity ] [ CHECK condition ]
CREATE INDEX	Creates a new index.	CREATE { [ UNIQUE ] [ HASH ] INDEX [ IF NOT EXISTS ] newIndexName     | PRIMARY KEY [ HASH ] } ON tableName ( indexColumn [,...] )
CREATE LINKED TABLE	Creates a table link to an external table.	CREATE [ [ GLOBAL | LOCAL ] TEMPORARY ] LINKED TABLE [ IF NOT EXISTS ] name ( driverString, urlString, userString, passwordString, [ originalSchemaString, ] originalTableString ) [ EMIT UPDATES | READONLY ]
CREATE ROLE	Creates a new role.	CREATE ROLE [ IF NOT EXISTS ] newRoleName
CREATE SCHEMA	Creates a new schema.	CREATE SCHEMA [ IF NOT EXISTS ] name [ AUTHORIZATION ownerUserName ]
CREATE SEQUENCE	Creates a new sequence.	CREATE SEQUENCE [ IF NOT EXISTS ] newSequenceName [ START WITH long ] [ INCREMENT BY long ] [ CACHE long ]
CREATE TABLE	Creates a new table.	CREATE [ CACHED | MEMORY ] [ TEMP | [ GLOBAL | LOCAL ] TEMPORARY ] TABLE [ IF NOT EXISTS ] name { { ( { columnDefinition | constraint } [,...] ) [ AS select ] }     | { AS select } } [ ENGINE tableEngineName ] [ TRANSACTIONAL ] [ NOT PERSISTENT ]
CREATE TRIGGER	Creates a new trigger.	CREATE TRIGGER [ IF NOT EXISTS ] newTriggerName { BEFORE | AFTER | INSTEAD OF } { INSERT | UPDATE | DELETE | SELECT | ROLLBACK } [,...] ON tableName [ FOR EACH ROW ] [ QUEUE int ] [ NOWAIT ] CALL triggeredClassName
CREATE USER	Creates a new user.	CREATE USER [ IF NOT EXISTS ] newUserName { PASSWORD string | SALT bytes HASH bytes } [ ADMIN ]
CREATE VIEW	Creates a new view.	CREATE [ OR REPLACE ] [ FORCE ] VIEW [ IF NOT EXISTS ] newViewName [ ( columnName [,...] ) ] AS select
DROP AGGREGATE	Drops an existing user-defined aggregate function.	DROP AGGREGATE [ IF EXISTS ] aggregateName
DROP ALIAS	Drops an existing function alias.	DROP ALIAS [ IF EXISTS ] existingFunctionAliasName
DROP ALL OBJECTS	Drops all existing views, tables, sequences, schemas, function aliases, roles, user-defined aggregate functions, domains, and users (except the current user).	DROP ALL OBJECTS [ DELETE FILES ]
DROP CONSTANT	Drops a constant.	DROP CONSTANT [ IF EXISTS ] constantName
DROP DOMAIN	Drops a data type (domain).	DROP DOMAIN [ IF EXISTS ] domainName
DROP INDEX	Drops an index.	DROP INDEX [ IF EXISTS ] indexName
DROP ROLE	Drops a role.	DROP ROLE [ IF EXISTS ] roleName
DROP SCHEMA	Drops a schema.	DROP SCHEMA [ IF EXISTS ] schemaName
DROP SEQUENCE	Drops a sequence.	DROP SEQUENCE [ IF EXISTS ] sequenceName
DROP TABLE	Drops an existing table, or a list of tables.	DROP TABLE [ IF EXISTS ] tableName [,...] [ CASCADE | RESTRICT ]
DROP TRIGGER	Drops an existing trigger.	DROP TRIGGER [ IF EXISTS ] triggerName
DROP USER	Drops a user.	DROP USER [ IF EXISTS ] userName
DROP VIEW	Drops an existing view.	DROP VIEW [ IF EXISTS ] viewName [ RESTRICT | CASCADE ]
TRUNCATE TABLE	Removes all rows from a table.	TRUNCATE TABLE tableName

SQL basics- complete reference guide - part1 - DML

Part1: DML-Data Manipulation Language

Command	Description	SYNTAX	Example
SELECT	Selects data from a table or multiple tables.	SELECT [ TOP term ] [ DISTINCT | ALL ] selectExpression [,...] FROM tableExpression [,...] [ WHERE expression ] [ GROUP BY expression [,...] ] [ HAVING expression ] [ { UNION [ ALL ] | MINUS | EXCEPT | INTERSECT } select ] [ ORDER BY order [,...] ] [ LIMIT expression [ OFFSET expression ] [ SAMPLE_SIZE rowCountInt ] ] [ FOR UPDATE ]
INSERT	Inserts a new row / new rows into a table.	INSERT INTO tableName [ ( columnName [,...] ) ] { VALUES { ( { DEFAULT | expression } [,...] ) } [,...] | [ DIRECT ] [ SORTED ] select }
UPDATE	Updates data in a table.	UPDATE tableName [ [ AS ] newTableAlias ] SET { columnName= { DEFAULT | expression } } [,...] [ WHERE expression ]
DELETE	Deletes rows form a table.	DELETE FROM tableName [ WHERE expression ]
BACKUP	Backs up the database files to a .	BACKUP TO fileNameString
CALL	Calculates a simple expression.	CALL expression
EXPLAIN	Shows the execution plan for a statement.	EXPLAIN { [ PLAN FOR ] | ANALYZE } { select | insert | update | delete | merge }
MERGE	Updates existing rows, and insert rows that don't exist.	MERGE INTO tableName [ ( columnName [,...] ) ] [ KEY ( columnName [,...] ) ] { VALUES { ( { DEFAULT | expression } [,...] ) } [,...] | select }
RUNSCRIPT	Runs a SQL script from a file.	RUNSCRIPT FROM fileNameString [ scriptCompression ] [ CIPHER cipher PASSWORD string ] [ CHARSET charsetString ]
SCRIPT	Creates a SQL script from the database.	SCRIPT [ SIMPLE ] [ NODATA ] [ NOPASSWORDS ] [ NOSETTINGS ] [ DROP ] [ BLOCKSIZE blockSizeInt ] [ TO fileNameString [ scriptCompression ]     [ CIPHER cipher PASSWORD string ] ] [ CHARSET charsetString ]
SHOW	Lists the schemas, tables, or the columns of a table.	SHOW { SCHEMAS | TABLES [ FROM schemaName ] |     COLUMNS FROM tableName [ FROM schemaName ] }

Scenarios in which Serialization cannot happen

What are the special cases in which serialization cannot happen?
-> There are following scenarios in which serialization cannot happen:
a. Variables are transient.
b. Variables are static.
c. Base class variables are serialized if class itself is serializable.

java prevent sql injection - using PreparedStatement

PreparedStatement is the best way to prevent sql injection in java, rather than escaping strings. 

Here's a simple example taking the user's input as the parameters:

public insertUser(String name, String email) {
   Connection conn = null;
   PreparedStatement stmt = null;
   try {
      conn = setupTheDatabaseConnectionSomehow();
      stmt = conn.prepareStatement("INSERT INTO person (name, email) values (?, ?)");
      stmt.setString(1, name);
      stmt.setString(2, email);
      stmt.executeUpdate();
   }
   finally {
      try {
         if (stmt != null) { stmt.close(); }
      }
      catch (Exception e) {
         // log this error
      }
      try {
         if (conn != null) { conn.close(); }
      }
      catch (Exception e) {
         // log this error
      }
   }
}

No matter what characters are in name and email, those characters will be placed directly in the database. They won't affect the INSERT statement in any way.

There are different set methods for different data types -- which one you use depends on what your database fields are. For example, if you have an INTEGER column in the database, you should use asetInt method. The PreparedStatement documentation lists all the different methods available for setting and getting data.

redirect message to IO stream

How could Java classes direct program messages to the system console, but error messages, say to a file?
The class System has a variable out that represents the standard output, and the variable err that represents the standard error device. By default, they both point at the system console. This how the standard output could be re-directed:

Stream st = new Stream(new FileOutputStream("output.txt")); 
System.setErr(st);
System.setOut(st);

java socket connect read string

Java - create socket connection to HOST:PORT and read message from there

import java.io.*;
import java.net.*;
import java.util.*;

public class Time_Server_Socket_Test_Java {
    public static void main(String[] args) {
        try {
            Socket s = new Socket(HOST, PORT);//use your own HOST:PORT
            try {
                InputStream inStream = s.getInputStream();
                Scanner in = new Scanner(inStream);

                while (in.hasNextLine()) {
                    String line = in.nextLine();
                    System.out.println(line);
                }
            } finally {
                s.close();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

How to serialize variables selectively

In a Java class, one has 10 variables. One wants to serialize only 3 variables,how can this be achieved?
->Make variables as 'transient' which are not to be serialized.

maximize a JFrame window in java

How to Maximize a JFrame :

 
    JFrame myFrame = new JFrame();
    myFrame.setVisible(true);
    myFrame.setExtendedState(myFrame.getExtendedState() | JFrame.MAXIMIZED_BOTH);
    

The usage of Java packages.

Explain the usage of Java packages.

A. This is a way to organize files when a project consists of multiple modules. It also helps resolve naming conflicts when different packages have classes with the same names. 

Packages access level also allows you to protect data from being used by the non-authorized classes.

Java: difference between private, protected, and public?

These keywords are for allowing privileges to components such as java methods and variables.
Public: accessible to all classes
Private: accessible only to the class to which they belong
Protected: accessible to the class to which they belong and any subclasses.

Access specifiers are keywords that determines the type of access to the member of a class. These are:
* Public
* Protected
* Private
* Defaults

java show window JFrame JDialog always on top

We have to use this feature of java.awt.Window : Window.alwaysOnTop(boolean); Example code :

import javax.swing.JFrame;
import javax.swing.JLabel;

public class Always_on_Top_JFrame_JAVA{
    public static void main(String[] args) {
        JFrame frame = new JFrame("Title - always on top :D ");
        // Set's the window to be "always on top"
        frame.setAlwaysOnTop( true );

        frame.setLocationByPlatform( true );
        frame.add( new JLabel(" Always on TOP ") );
        frame.pack();
        frame.setVisible( true );
    }
}

Order of catching exception in java

Does it matter in what order catch statements for FileNotFoundException and IOExceptipon are written?

A. Yes, it does. The FileNotFoundException is inherited from the IOException. 

Exception's subclasses have to be caught first.

Exception

^

|

IOException

^

|

FileNotFoundException 

So while catching exceptions, we must catch the low level exception first - here : FileNotFoundException .

#The hierarchy in Java Exception framework :

wrapper classes in Java

Describe the wrapper classes in Java.Wrapper class is wrapper around a primitive data type. An instance of a wrapper class contains, or wraps, a primitive value of the corresponding type.

Following table lists the primitive types and the corresponding wrapper classes:

Primitive - Wrapper

boolean  - java.lang.Boolean

byte - java.lang.Byte

char - java.lang.Character

double - java.lang.Double

float - java.lang.Float

int - java.lang.Integer

long - java.lang.Long

short - java.lang.Short

void - java.lang.Void

Java Class as Applet as well as Application

Can you write a Java class that could be used both as an applet as well as an application?
A. Yes. Add a main() method to the applet.

Bring JFrame JDialog Window to front java swing

To bring JFrame or JDialog ... or Window (JFrame and JDialog inherits Window)   to front in JAVA, fun the code below :

java.awt.EventQueue.invokeLater(new Runnable() {
    @Override

    //myFrame is object of Window or JFrame
    public void run() {
        myFrame.toFront();
        myFrame.repaint();
    }
});

Redirect Standard System Output and Error Message to PrintStream in Java

In a Java program, how can you divert standard system output or error messages, say to a file?
->We can achieve this by using
public static void setErr(PrintStream err)
and public static void setOut(PrintStream out) methods.
By default, they both point at the system console. The following example redirects Out and Err messages to 'error.txt'  file

Stream stream = new Stream(new FileOutputStream("error.txt"));
System.setErr(stream);
System.setOut(stream);

You can redirect the Err and Out stream to any PrintStream object.

concatenate arrays of any type - java

Combining two arrays of any type

 public static  T[] concat(T[] first, T[] second) {
  T[] result = Arrays.copyOf(first, first.length + second.length);
  System.arraycopy(second, 0, result, first.length, second.length);
  return result;
 }

For combining arbitrary number of arrays

difference between an interface and an abstract class

What's the difference between an interface and an abstract class? Also discuss the similarities. (Very Important)
Abstract class is a class which contain one or more abstract methods, which has to be implemented by sub classes. Interface is a Java Object containing method declaration and doesn't contain implementation. The classes which have implementing the Interfaces must provide the method definition for all the methods
Abstract class is a Class prefix with a abstract keyword followed by Class definition. Interface is a Interface which starts with interface keyword.
Abstract class contains one or more abstract methods. where as Interface contains all abstract methods and final declarations
Abstract classes are useful in a situation that Some general methods should be implemented and specialization behavior should be implemented by child classes. Interfaces are useful in a situation that all properties should be implemented.

Differences are as follows:
* Interfaces provide a form of multiple inheritance. A class can extend only one other class.
* Interfaces are limited to public methods and constants with no implementation. Abstract classes can have a partial implementation, protected parts, static methods, etc.
* A Class may implement several interfaces. But in case of abstract class, a class may extend only one abstract class.
* Interfaces are slow as it requires extra indirection to to find corresponding method in in the actual class. Abstract classes are fast. 

Similarities:
* Neither Abstract classes or Interface can be instantiated.


How to define an Abstract class?
A class containing abstract method is called Abstract class. An Abstract class can't be instantiated.
Example of Abstract class:

abstract class testAbstractClass { 
    protected String myString; 
    public String getMyString() { 
    return myString; 
} 
public abstract string anyAbstractFunction();
}

How to define an Interface?Answer: In Java Interface defines the methods but does not implement them. Interface can include constants. A class that implements the interfaces is bound to implement all the methods defined in Interface.
Example of Interface:

public interface sampleInterface {
    public void functionOne();
    public long CONSTANT_ONE = 1000;
}

Adding image to JPanel Java

Adding Image to JPanel

BufferedImage myPicture = ImageIO.read(new File("path-to-file"));
JLabel picLabel = new JLabel(new ImageIcon( myPicture ));
add( picLabel );

:D

Read time from internet time server - working java code

Read time from internet time server - working java code

import java.io.*;
import java.net.*;
import java.util.*;

/**
 * This program makes a socket connection to the atomic clock in Boulder,
 * Colorado, and prints the time that the server sends.
 */
public class Time_Server_Socket_Test_Java {
    public static void main(String[] args) {
        try {
            Socket s = new Socket("time-A.timefreq.bldrdoc.gov", 13);
            try {
                InputStream inStream = s.getInputStream();
                Scanner in = new Scanner(inStream);

                while (in.hasNextLine()) {
                    String line = in.nextLine();
                    System.out.println(line);
                }
            } finally {
                s.close();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

iterate through map hashmap linkedhashmap in java

How to iterate through Map.. MashMap, LinkedHashMap ...  in Java
Method 1 : If you're only interested in the keys, you can iterate through the keySet() of the map:

Map map = ...;

for (String key : map.keySet()) {
    // ...
}

Method 2 :

java escape text in regular expression

Java's a built-in way to escape arbitrary text so that it can be included in a regular expression-
For example, users enter "$5", we can match that exactly rather than a "5" after the end of input.


Just do this : to escape text in regex

Pattern.quote("$5");

use of @override annotation in java - why ?

The @override annotation  is most useful as a compile-time reminder that the intention of the method is to override a parent method. See this example:

import java.util.HashSet;
import java.util.Set;
/**
 * Override_Annotation_Usage_Example, from  Effective Java
 */

java reflection - what is - 101 tutorial

The name reflection is used to describe code which is able to inspect other code in the same system (or itself).

A simple code example of this in Java (imagine the object in question is foo) :

Method method = foo.getClass().getMethod("doSomething", null);
method.invoke(foo, null);

One very common use case in Java is the usage with annotations. JUnit 4, for example, will use reflection to look through your classes for methods tagged with the @Test annotation, and will then call them when running the unit test.

There are some good reflection examples to get started : at http://java.sun.com/developer/technicalArticles/ALT/Reflection/index.html

Bubble sort working source code - C/C++

Bubble sort working source code - C/C++

#include <stdio.h>
#include <iostream.h>

void bubbleSort(int *array,int length)//Bubble sort function 
{
    int i,j;
    for(i=0;i<length;i++)
    {
        for(j=0;j<i;j++)
        {
            if(array[i]>array[j])
            {
                int temp=array[i]; //swap 
                array[i]=array[j];
                array[j]=temp;
            }
        }
    }
}

void printElements(int *array,int length) //print array elements
{
    int i=0;
    for(i=0;i<length;i++)
        cout<<array[i]<<endl;
}


void main()
{

    int a[]={9,6,5,23,2,6,2,7,1,8};   // array to sort 
    bubbleSort(a,10);                 //call to bubble sort  
    printElements(a,10);               // print elements 
}