File IO operations with java programming language

File Management in OS

File management includes files and folders creation, copy and paste operations, reading the file and writing into files and deleting the files and folders 

And also reading meta data about files and folders. It may include file free space, occupied space and read/write permissions etc.

These above operations are considered as file management and managed by respective operating system.

GUI that represents Windows File Manager

File Management with Java 

Though Java is platform independent, programming language depends on native file IO resources of operating system.

This is possible with the Java API support. These API are categorized into 2 types.

1. Readers and Writers: Readers and writers does the IO operations, character by character
2. InputStream and OutputStream: Where as InputStream and OutputStream does IO operations byte by byte

Below are simple Java programs that demonstrates different File IO operations.

Program for creating directory

package com.allabtjava.fileio;

import java.io.BufferedReader;

import java.io.BufferedWriter;

import java.io.File;

import java.io.FileReader;

import java.io.FileWriter;

import java.io.IOException;

import java.nio.file.Path;

public class FileManager {

public FileManager() {

}

public void makeDirectory(String path, String dirName) {

Path dirPath = Path.of(path, dirName);

File dir = new File(dirPath.toString());

boolean isCreated = dir.mkdir();

if (isCreated)

System.out.println("A new directory with the name " + dir.getPath() + " created!");

}

        public static void main(String args[]) throws IOException {

FileManager manager = new FileManager();

manager.makeDirectory("e:\\", "students");

}

}

Program for creating file:

package com.allabtjava.fileio;

import java.io.BufferedReader;

import java.io.BufferedWriter;

import java.io.File;

import java.io.FileReader;

import java.io.FileWriter;

import java.io.IOException;

import java.nio.file.Path;

public class FileManager {

public FileManager() {

}

public void createFile(String dirPath, String dirName, String fileName) throws IOException {

Path filePath = Path.of(dirPath, dirName, fileName);

File file = new File(filePath.toString());

boolean isFileCreated = file.createNewFile();

if (isFileCreated)

System.out.println("A new file with the name " + file.getPath() + " created!");

}

        public static void main(String args[]) throws IOException {

FileManager manager = new FileManager();

manager.createFile("e:\\", "students", "student_1");

}

}

Listing all files available in given folder

package com.allabtjava.fileio;

import java.io.BufferedReader;

import java.io.BufferedWriter;

import java.io.File;

import java.io.FileReader;

import java.io.FileWriter;

import java.io.IOException;

import java.nio.file.Path;

public class FileManager {

public FileManager() {

}

     public void listFiles(String dirPath, String dirName) {
Path dir = Path.of(dirPath, dirName);
File file = new File(dir.toString());
String[] listOfAllFiles = file.list();
System.out.println("List of all Files in the directory/folder - " + dirName + ": ");
for (String fileName : listOfAllFiles) {
System.out.println(fileName);
}
}

        public static void main(String args[]) throws IOException {

FileManager manager = new FileManager();

manager.listFiles("e:\\", "pinterest");

}

}

Delete a directory

package com.allabtjava.fileio;

import java.io.BufferedReader;

import java.io.BufferedWriter;

import java.io.File;

import java.io.FileReader;

import java.io.FileWriter;

import java.io.IOException;

import java.nio.file.Path;

public class FileManager {

public FileManager() {

}

     public void deleteDirectory(String dirPath, String dirName) {

Path dir = Path.of(dirPath, dirName);

File dirToBeDeleted = new File(dir.toString());

if (dirToBeDeleted.exists()) {

boolean isDeleted = dirToBeDeleted.delete();

if(isDeleted)

System.out.println("File deleted!");

else

System.out.println("Could not delete file. File is being used by other program or application.");

}

}

        public static void main(String args[]) throws IOException {

FileManager manager = new FileManager();

manager.deleteDirectory("e:\\", "pinterest");

}

}

Read a file content

package com.allabtjava.fileio;

import java.io.BufferedReader;

import java.io.BufferedWriter;

import java.io.File;

import java.io.FileReader;

import java.io.FileWriter;

import java.io.IOException;

import java.nio.file.Path;

public class FileManager {

public FileManager() {

}

     public void readFile(String dirPath, String dirName, String fileName) throws IOException {

Path filePath = Path.of(dirPath, dirName, fileName);

File file = new File(filePath.toString());

FileReader reader = new FileReader(file.getAbsolutePath());

BufferedReader bufferedRead = new BufferedReader(reader);

String line = null;

while((line = bufferedRead.readLine()) != null) {

System.out.println(line);

}

bufferedRead.close();

}

        public static void main(String args[]) throws IOException {

FileManager manager = new FileManager();

manager.readFile("e:\\", "pinterest", "demo.txt");

}

}

Write content into file

package com.allabtjava.fileio;

import java.io.BufferedReader;

import java.io.BufferedWriter;

import java.io.File;

import java.io.FileReader;

import java.io.FileWriter;

import java.io.IOException;

import java.nio.file.Path;

public class FileManager {

public FileManager() {

}

     public void writeToFile(String dirPath, String dirName, String fileName) throws IOException {

Path filePath = Path.of(dirPath, dirName, fileName);

File file = new File(filePath.toString());

FileWriter writer = new FileWriter(file);

BufferedWriter bufferedWriter = new BufferedWriter(writer);

bufferedWriter.write("allabtjava.com is a web site, has information about java technologies \n");

bufferedWriter.write("This article explains about, files and IO management with java programming language.");

bufferedWriter.close();

}

        public static void main(String args[]) throws IOException {

FileManager manager = new FileManager();

manager.writeToFile("e:\\", "pinterest", "demo.txt");

}

}

Agile Methodology with SCRUM Framework Basics

Software development activities can be managed and taken care with different life cycle models. These life cycle models has became legacy since few years. Few of the available Software Development Life Cycle Models in short SDLC are Win-Win Model and Waterfall Model etc.

These traditional models has different phases of development. 

       1. Requirements 

       2. Analysis 

       3. Design 

       4. Implementation 

       5. Test 

       6. Documentation 

and 7. Maintenance 

In SDLC, the above stages are freezed one after the other. If developer is in Design phase and realized that there could be a possibility of change in requirements, then it is not possible to go back one phase and fix in Requirement phase. 
These scenarios and use cases has brought Agility in to existence in software development activities.  

Agility in English: 

Agility means "able to move quickly and easily".  Being agile in software development makes the development move or progressed quick enough and flexible to go back and forth through out the development phases and complete the activities on time.

Agile Methodology:

"Agility is the ability that gives better productivity..."

Agile is the ability to create and respond to change. It is a way of dealing with and ultimately succesing in an uncertain environment. Agile methodology has different subsets also called as frameworks. 
SCRUM and Kanban are few among others. These frameworks can be adapted as process solutions based upon different development needs.

SCRUM Framework:

Scrum is a process framework used to manage product development and other knowledge work.

SCRUM framework manages the development activities biweekly, 3 weeks or 4 weeks. This duration is called as Sprint. Usually it is not recommended to have more than 6 members or developers in a team.

Sprint:

Sprint is a duration of time where few backlogs are realized as tasks and completed by development team. Once the Sprint is completed these software changesets goes into release version of the application software.
Based on the need Sprint duration can be 2 or 3 or 4 weeks. But most of the Scrum experts suggest Biweekly sprints.

SCRUM and Meetings:

    1. Standup call

    2. Review Meeting

    3. Grooming Session

    4. Retrospective

Standup calls are held everyday morning that lasts for 15 minutes. And following are discussed:

    1. What is done yesterday?

    2. What is planned today?

    3. Any Roadblocks?

NOTE: It is not recommended to consider more than 15 minutes for Standup meeting

Review Meeting is held at the end of the Sprint showing different works and demos of Sprint's development activites.

Grooming Session lasts for one and half hours. During this session tasks are pulled from backlogs and discussed the following:

    1. Estimations for the Tasks

    2. Deciding the priorities

    3. Severity levels

    4. Assignments

Retrospective meetings are held after the end of Sprint and discussed about:

    What went correct..?

    What went wrong..?

And Appreciations if any...

     

Scrum framework and few notable points:

1. All requirements are consolidated as backlogs along with its descriptions and other details.
2. Estimations of backlogs are done with the Poker Cards
3. Poker cards are numbered in a Fibonacci order
4. SCRUM is managed by Certified SCRUM Master or SCRUM Coach
5. If Standups are not held with in 15 minutes, can be considered as limitation.
6. Virtual Boards are considered over Physical boards, if members are in remote locations 

SCRUM and Agile Supporting Tools:

1. Microsoft Azure Boards
2. Atlassian JIRA
3. IBM - Rational Team Concert 

SCRUM Limitations:

• Geographically if team members are located in different places, Agile may not be effective

Coding and best practices

 Write code or write code in right way...

Writing a coding solution to a problem can be done in many ways. If the solution can be obtained with less number of code lines, then it is easy to understand and maintain.

But what if code is large with having millions of lines. Moreover maintenance and readability becomes difficult as the code base grows... Right? 

In this blog I want to share my views and experiences on writing code efficiently and effectively with less maintenance efforts.

Aspects to consider while coding:

• Naming convention
• Cyclomatic Complexity
• SOLID principles
• DRY Principle
• Managing dead code
• Comments

Naming conventions:

Every programming language mandates few norms in order to name variables, classes and functions etc. For ex: Java uses class names first letter to be a alphabet and rest to be lower case letters. 

But if we dig little bit more, naming conventions are not limited to only upper case or lower case letters and using alphanumeric letters etc.

Naming a variable must be enough concise as naming your first child's name...

Few bad names for variables and constants:

          int final static TWO = 2;  [wrong]

          int final static MAX_LENGHT = 2; [Correct] 

  

Cyclomatic Complexity:

Cyclomatic complexity is a measure or metric to estimate complexity level of a snippet or block of code. 

Cyclomatic complexity and best practices:

• Never put more than three conditional checks (&& operator and || operator etc.) in one if condition
• Never exceed more than thirty lines in one function or method.
• Never exceed more than 1000 lines in one class or one file.

SOLID principles:

Usually developing a large and scalable application, requires better design. Adhering to SOLID principles yields better scalable and easily maintainable applications.

There are five SOLID principles. They are:

1. Single Responsibility Principle
2. Open/Closed Principle
3. Liskov's Substitution Principle
4. Interface Segregation Principle
5. Dependency Inversion Principle

DRY Principle:  

DRY stands for Do Not Repeat Yourself. Sometimes, There could be a need to use same or similar set of lines of code to be used multiple times in the same application. For ex. String utilities, DB connections or updating records in database etc.

Writing frequently used code snippets multiple times is not a good practice. Instead move this code to a function or method and use this method in places where ever required.

Simple use cases are:

• DB Connections
• File IO Operations
• String Utilities etc. 

Managing Dead Code:

Sometimes there are some lines or instructions in code base, which are completely not executed in all cases at all. This is considered as dead code. 

Dead code reduces the quality with respect to the readability.  

Comments:

Comments increases the readability of the program for programmers. Comments are written at class level, method level and variable level [Constants, instance variables and class variables] differently. 

The reason for this difference is, the pattern of comments is identified by API document generator tools and generates API documents.

Conclusion:

What all I tried to share through this post is, writing code for a specific problem can be done in different ways. But making sure that the program is more readable, maintenance free and easily scalable is also very important. 

The above few solutions or hacks will definitely help in developing better applications. 

Hope you enjoyed reading the post. Comments are welcomed. Thank you!! 

Happy coding!...

Exception handling and java keywords

Exception:

Exception in a programming language and in English language is pretty similar. Exception means being different from or not following the rules. And in programming language like Java, exception is  an event which occurs during the execution of a program that disturbs the complete flow of application or program.

When something beyond expected happens while executing a program is considered as an error. handling these errors or abnormality is called as Exception handling.

Exception Handling:

Exception handling in java is managed with the help of java keywords and java API support.. 

            1. Java Keywords

            2. Java API support

Java Keywords: 

There are 5 keywords in Java.

          1. Try

          2. catch

          3. finally

          4. throw

   and 5. throws

These five keywords used all together or combination of few keywords are used on need basis.

1. Try:

The code or set of instructions which are prone to errors or exceptions are enclosed in try block.

For example dividing a five or some number with zero [5/0]. The result of 5/0 is undefined and in Java,  this scenario is considered as exception.

2. Catch:

Usually try block is followed by a catch block. If some exception is occurred in try block, the execution control is moved to catch block instead of  continuing the execution of  try block's code. 

The purpose of catch block is, handling the exceptions that are raised in try.

There is a possibility of handling multiple scenarios in multiple catches. 

NOTE: Multiple catches can be written for single try.

Java code example:

           try{

                   ---                     // code

                } catch(OtherException e) {

                   ---                    // code

               }catch(AnotherException e) {

                }      

3. Finally:

Usually if there is an exception in try block, the rest of the lines in try are not executed and control moves on to catch block. And if there is no exception at all in try block control never moves to catch block. Then catch block is considered to be dead code. 

Then where must we write mandatory code? 

So, finally block is written after try and catch which gets executed always. 

Java code example:

            try{

                  ---

                } catch (Exception e) {

                  ---

                } finally{

                  ---              // mandatory code for execution

                } 

NOTE: Always put mandatory code in finally block. For example: closing IO resources connections like network and database connections etc

4. Throws and Throw:

Throws and throw keywords works along with Java API support. I will explain the Java API support for Exception handling in next subsequent articles. 

For now, we can understand that for every exception scenario there is one Java class(Java API). Example: Number divided by zero. [5/0]. The result is ArithmeticException

Java code example:

     try{

               int result = 5/0;

                ---        // other code

         }catch(ArithmeticException e) {

                ---        // exception of try block is handled here   

         }  

  Why there is no "throws" keyword here....?

The alternative solution for above snippet with throws and throw for checking election voting age eligibility exception is:

void votingAgeNumber() throws ArithmeticException{

                int age = 12; 

                if(age <=18) {

                           throw new ArithmeticException("Age is not sufficient to vote");

                 }

                 ---       // other code              

           }

NOTE: Sometimes "throws" keyword works as an alternative solution for try and catch blocks. The throws keyword is used instead of try and catch.

Example:

Solution with throws:

void divideNumber() throws ArithmeticException{

         int result = 5/0;

 } 

 And snippet with try and catch:        

void divideNumber(){

   try{

      int result = 5/0;

    }catch(ArithmeticException e){

     ----      // handle exception

    }

} // method end                      

         

The above both solutions are same, but with different keywords.


 Some key points:

1. There can be one try with multiple catch blocks.

2. Try block can be followed by either catch or finally block.

3. Or both can be followed

4. Throws is like warning that exception can be thrown and throw keyword is real accident took place.

I wrote here  https://www.allabtjava.com/2021/01/java-api-support-for-exception-handling.html on checked exceptions and runtime or unchecked exceptions.

Happy coding... :)

   

Java and OOPS concepts

Java is an object oriented programming language which can be downloaded and installed in your local Machine from java.com

To explain java binaries and tools requires block diagram which gives clear picture. For now I brief few important tools.

• JDK - java development toolkit
• JVM - Java virtual machine
• JRE - Java Run time environment

From oracle site we can download JDK which is shipped along with JVM and JRM. Mostly java programmers need the JDK. For end users JRE alone is enough.

Basic OOPS characteristics are

Inheritance

Encapsulation

Abstraction

and Polymorphism

The above concepts collectively makes application software extendable and changeable with less effort.
Also helps in Developing design patterns. Design patterns gives solutions for common challenges usually a programmer faces while development applications.
Factory design pattern, Abstract design pattern, Builder pattern etc. I explain these Design patterns in another article.

Inheritance:
Inheritance is all about reusing one class behavior and members in it's child class. In java terminology these classes are called as super class and sub class. If class B extends class A then, class A becomes super class and class B becomes class A's sub class.

public class A{

  public A(){

 }

   -------

}

public class B extends A{

   public B(){

    } 

    -------

}   

Encapsulation:
Encapsulation is a technique of putting the source code all together within a unit. Java uses class and interface as keywords to represent unit. Data Hiding is one of the buzzwords which is possible only with implementation of Encapsulation in the program.

Abstraction:
Abstraction is the concept of hiding the irrelevant data from client/user visibility. To implement this feature java uses abstract keyword. this can be be prefixed to a class and methods. Once the class is abstract class then it's object can not be created. And id one or all methods of same class are followed by abstract keyword it can not be implemented.
The point here is java programming language gives implementation freedom to the developers where ever expected.
Sometimes java program is written to a another programmer rather a end user. Usually this code is called Application programming interface in short API. When a programmer writes a program with the intention to be used by another programmer, He/She may not need all the details [line by line] instruction's description is not required. Right?
The punch line is abstraction helps in showing only relevant data to the client of our program.
One of the mostly used design pattern is abstract factory design pattern.

Polymorphism:
In generic terminology poly means many morph means forms. It means many forms of a single method names.
Polymorphism can be achieved within the class or using inheritance i.e extends keyword.

Overloading and overriding:

Overloading rules:
within the class a same method can be duplicated but accepts different arguments and returns different result

1.       Number of arguments must be different
2. Or  Sequence of arguments must be different
3. Or  Type of the arguments must be different.

Uses:
Let us take a method .
     int add(int a, int b){

        return a+b;

     }

Now let us overload this method to add decimal values
 float add(float a, float b){

     return a+b;

 }

Now based on the arguments passed to the add() respect add() method will be invoked.
Overriding:
Overriding is possible only by using inheritance.For an instance super class has add(int a, int b). and sub class also needs add operation but computes differently. Then programmer simply overrides the add() of super class overrides the add() with his new implementation. 

public class SuperClass{

  int add(int a, int b){

       ....

   }

}

public Subclass extends SuperClass{

@Overrides

int add(int a, int b){

// computes his own add operation

}

} 

In next article I write about tools of JDK and JRE and internals of JVM Java Virtual Machine.

Please click the link for more good look and feel and elegant font

Happy Coding. ;-)

Core Java: Immutable objects and mutable objects with an example

Immutable objects and mutable objects with an example 

In object oriented programming language in short OOPS, every problem, precisely every requirement is viewed as an object. Understanding the problem in this point of view brings many good things possible in programming like encapsulation, abstraction, polymorphism and inheritance. Anyways this post is not intended for describing benefits of OOPS.

Object could be any thing. Let us take Car for an instance. Basically car is an object and it has name, wheels, metal body, engine, maximum speed,  gear box etc as properties.

Let us consider the car name is Ferrari, maximum speed is 200 km per hr with 6 gears. While driving the car driver can change the speed of the car and change the gear etc.
So while car is running it's current speed, current gear are considered to be state of the object.
The current speed can be changed using accelerator and gear can be changed using gear box. These can be considered as behavior of the car object. Of course car has a name as well.

 Every object has 3 characteristics they are State, Behavior and Name. 

In our example Ferrari is name of the object. Number of gears, current gear, current speed are State and accelerator and gear box decides the behavior of the car object. In java language object's reference name is name of object and methods which decides state are behavior.  

ImmutableObject ferrari = new ImmutableObject("Ferrari", 200, "Red");

             1. new operator creates the object

             2. ferrari is name of object

             3. Ferrari, 200, and Red are State of object

Objects based upon it's behavior can be categorized into two types. They are 

              1. Immutable objects and 

              2. Mutable objects

Mutable and Immutable objects

Mutable object's state can be changed at run time, where as immutable object's state can not be changed. String class is the ideal example for immutable objects. 

    

The state of an object can be decided at it's creation time or at run time or at both times. If state is decided at creation time and it is restricted not be changed at run time, this object is considered to be an  immutable object. If this can be changed at run time, it is called as mutable object.

If car is automatic [no gears] and it's speed can not be changed at any time, then it is immutable car object.  

Below program creates immutable objects:

01  public final class ImmutableObject {
02
03  private String name;
04
05  private int maxSpeed;
06
07  private String color;
08
09  /**
10  * @param name
11  *            holds car name
12  * @param maxSpeed
13  *            holds maximum speed of the car
14  * @param color
15  *            holds color of car
16  */
17  public ImmutableObject(String name, int maxSpeed, String color) {
18  this.name = name;
19  this.maxSpeed = maxSpeed;
20  this.color = color;
21  }
22
23  public String getName() {
24  return name;
25  }
26
27  public int getMaxSpeed() {
28  return maxSpeed;
29  }
30
31  public String getColor() {
32  return color;
33  }
34
35  public static void main(String[] args) {
36  ImmutableObject ferrari = new ImmutableObject("Ferrari", 200, "Red");
37  System.out.println("Car name: " + ferrari.getName());
38  System.out.println("Car color:" + ferrari.getColor());
39  System.out.println("Car maximum speed:" + ferrari.getMaxSpeed());
40  System.out.println();
41
42  ImmutableObject anotherCar = new ImmutableObject("BMW", 180, "White");
43  System.out.println("Car name: " + anotherCar.getName());
44  System.out.println("Car color:" + anotherCar.getColor());
45  System.out.println("Car maximum speed:" + anotherCar.getMaxSpeed());
46  }
47  }
48

Output:

Car name: Ferrari
Car color:Red
Car maximum speed:200

Car name: BMW
Car color:White
Car maximum speed:180

Explanation

Line 1: First and fore most rule is to make your class final class.

Line 3 to Line 7: All variables are private variables. private access modifier restrics usage of members within the class

Note: Do not use other classes as data types of your instance variables which are mutable in behavior. All of our example variables are of String type. String is immutable. See API document of String class for more information.   

Line 17: Creates parameterised constructor with state which can not be changed at run time

Line 23 to Line 33: Create only those methods which shares it's state to the other classes. As we did in our example ImmutableObject. Allows only getter methods and no setter methods at all.


Line 36 to Line 42: Finally, create 2 objects ferrari and another car with different state which can not be changed at run time..

Now, let us change the same class which allows creating mutable objects:

01
02 public class MutableObject {
03
04 private String name;
05
06 private int maxSpeed;
07
08 private String color;
09
10 private int currentGear;
11
12 private int currentSpeed;
13
14 /**
15 * @param name
16 *            holds car name
17 * @param maxSpeed
18 *            holds maximum speed of the car
19 * @param color
20 *            holds color of car
21 */
22 public MutableObject(String name, int maxSpeed, String color) {
23 this.name = name;
24 this.maxSpeed = maxSpeed;
25 this.color = color;
26 }
27
28 public String getName() {
29 return name;
30 }
31
32 public int getMaxSpeed() {
33 return maxSpeed;
34 }
35
36 public int getCurrentGear() {
37 return currentGear;
38 }
39
40 public void setCurrentGear(int currentGear) {
41 this.currentGear = currentGear;
42 }
43
44 public int getCurrentSpeed() {
45 return currentSpeed;
46 }
47
48 public void setCurrentSpeed(int currentSpeed) {
49 this.currentSpeed = currentSpeed;
50 }
51
52 public String getColor() {
53 return color;
54 }
55
56 public static void main(String[] args) {
57 MutableObject ferrari = new MutableObject("Ferrari", 200, "Red");
58 System.out.println("Car name: " + ferrari.getName());
59 System.out.println("Car colo: " + ferrari.getColor());
60 System.out.println("Car maximum speed:" + ferrari.getMaxSpeed());
61
62 ferrari.setCurrentGear(5);
63 ferrari.setCurrentSpeed(150);

64 System.out.println(String.format("Current speed is %s and current gear is %s \n", ferrari.getCurrentSpeed(), ferrari.getCurrentGear()));

65
66
67 ferrari.setCurrentGear(1);
68 ferrari.setCurrentSpeed(10);
69 System.out.println(String.format("Changed state at run time!.. \nCurrent speed is %s and current gear is %s ", ferrari.getCurrentSpeed(), ferrari.getCurrentGear()));

70

71

72 System.out.println();
73
74 }
75}
76

Output:

Car name: Ferrari

Car colo: Red

Car maximum speed:200

Current speed is 150 and current gear is 5 

Changed state at run time!.. 

Current speed is 10 and current gear is 1 

Explanation

  

Line 2: Remove final keyword. This makes the class extendable using extend keyword

Line 10 to Line 12: Introduced new variables which adds new information to the state of object

Line 40 and Line 48: Introduced new setter methods which changes state at run time.

Line 57: Finally, create the ferrari object and change it's state run time by calling different setter methods.

Line 62 to Line 72: Changes the state by calling setters on member variables.  

Few more details about immutable objects:

• It is always good practice to use immutable objects in our application especially in concurrent apps where ever applicable
• Immutable objects ensures correct results/output always in all environments like multi threading environment, collection framework.
• HashMap<key, value> always requires immutable object as key. Otherwise it behaves in undetermined way.
• Consider cloning when creating immutable classes. I will post another article about importance of deep cloning and shallow copy in details in near future.
• Cache memory implementation uses immutable objects 
• java.lang.String is the most used immutable class in java

    .

Swing JLabel demo with example

This article is continuation of previous post JFrame usage demo. Please read it before continuing.

This post uses the same example code shown in JFrame usage demo with JLabel changes and introduces layout manager BorderLayout.

Layout Manager:

Layout manager is responsible to arrange components on containers. Usually every swing container is created with a default layout manager but can be changed with setLayout() api. For example JFrame uses BorderLayout as default layout amanger.

Java program for JLabel

1 
2   import java.awt.BorderLayout;
3   import java.awt.Color;
4   import java.awt.Font;
5 
6   import javax.swing.JFrame;
7   import javax.swing.JLabel;
8   import javax.swing.SwingUtilities;
9 
10  /**
11   *
12   * Simple class to demonstrate JLabel of swing toolkit
13   *
14   * @author Nagasharath
15   *
16   */
17  public class LabelDemo extends JFrame {
18
19  private final String title = "It's all abt java!...  ";
20
21  private JLabel label;
22
23  /**
24  * set properties of the main window. Title, size of frame and position/location
25  */
26  public LabelDemo() {
27  this.setTitle(title);
28  this.setSize(300, 200);
29  this.setLocationRelativeTo(null);
30  initComponents();
31  }
32
33  /**
34  * instantiates controls controls.
35  *
36  */
37  private void initComponents() {
38  BorderLayout layout = new BorderLayout(20, 10);
39  this.setLayout(layout);
40
41  label = new JLabel("java-gui.blogspot.com");
42  label.setForeground(Color.RED);
43  label.setFont(new Font(Font.MONOSPACED, Font.BOLD, 25));
44  this.getContentPane().add(label, BorderLayout.CENTER);
45  }
46
47  public static void main(String[] args) {
48
49  Runnable r = () -> {
50  LabelDemo demo = new LabelDemo();
51  demo.setVisible(true);
52  };
53  SwingUtilities.invokeLater(r);
54  }
55  }
56


Line 21: Introduced new variable of type JLabel

Line 38 and Line 39: Used BorderLayout as layout manager to arrange label component on JFrame container

Line 41: Instantiated label with a text of String type.

Line 42 and Line 43:  label properties like foreground color, font style, size, type and background etc are specified

Line 44:  Finally added this label to the JFrame using add().

Output:

JFrme with JLabel

Java Multi threaded programming basics with Reentrant lock

Java Multi threaded programming basics with Reentrant locks

As we have seen in earlier post that implicit locking mechanism achieved using synchronized keyword slows down the application performance. Hence java concurrency api gives explicit locking mechanism to achieve mutual exclusion among shared object.

How using explicit locks are better than implicit lock?

• Explicit lock acquires lock per Thread basis and not per method invoke basis. It is inverse in the case of implicit lock.  
• If a method is synchronized then every invocation of that method involves acquiring and releasing of lock. This process really slows down the application performance. 
• Hence it is always good idea to prefer reentrent lock or explicit lock to implicit lock.
• ReentrantLock is a class available in java.util.concurrency package
• lock() and unlock() methods are used used to acquire and release the lock.
• Condition class is used in place of Object class wait(), notifyAll() and notify().
• signal() and await() of Condtion are used mostly 

Let's see the  Java Multi threaded programming basics Producer and Consumer Problem's solution with Reentrent lock.

import java.util.Iterator;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;

/**
 * In {@code BufferImpl} we have seen thread safe 
 * buffer implementation using implicit lock/ synchronization block
 * 
 * This {@code BufferImpl_conc} we see same implementation replacing implicit
 * lock with concurrency utility classes Reentrant Locks
 * 
 * Buffer implementation with ArrayList and with Producer consumer 
 * problem implementation
 * 
 * @author Nagasharath
 *
 */

public class BufferImpl_conc {

   private CopyOnWriteArrayList<String> buffer;
   private final short SIZE = 10;
   private boolean isBufferFull = false;
   private ReentrantLock lock;
   private Condition condition;

  public BufferImpl_conc() {
     buffer = new CopyOnWriteArrayList<String>();
     lock = new ReentrantLock();
     condition = lock.newCondition();
  }

 /**
  * @throws InterruptedException
  */
 private void producesFeed() throws InterruptedException {
    lock.lock();
    try {
       while (true) {
         if (isBufferFull) {
             System.out.println("Started Consuming!....\n");
             condition.signal();
             condition.await();
        }
        buffer.add(String.valueOf(System.nanoTime()));
        if (SIZE <= buffer.size()) {
              isBufferFull = true;
              Thread.sleep(10000);
              System.out.println("Buffer full. Production halts...\n");
       }
     }
    } finally {
        lock.unlock();
    }
 }

 /**
  * @throws InterruptedException
  */
 private void consumesFeed() throws InterruptedException {

    lock.lock();
    try {
       while (true) {
          Iterator<String> iter = buffer.iterator();
          while (iter.hasNext()) {
             String next = iter.next();
             System.out.println("Consuming element: " + next);
             buffer.remove(buffer.indexOf(next));
          }
          isBufferFull = false;
          System.out.println("Started producing!....");
          condition.signal();
          condition.await();
      }
   } finally {
      lock.unlock();
   }
 }

 /**
  * @author Nagasharath
  *
  */
 class ProducerThread extends Thread {
     @Override
    public void run() {
      try {
        producesFeed();
      } catch (InterruptedException e) {
      }
  }
 }


 /**
  * @author Nagasharath
  *
  */
 class ConsumerThread extends Thread {
  @Override
  public void run() {
    try {
      consumesFeed();
    } catch (InterruptedException e) {
    }
  }
 }

 public static void main(String[] args) {
   BufferImpl_conc impl = new BufferImpl_conc();
   ProducerThread producerThread = impl.new ProducerThread();
   ConsumerThread consumerThread = impl.new ConsumerThread();
   producerThread.start();
   consumerThread.start();
 }
}

Most parts of the program are same as we used in the post Java Multi threaded programming basics It is advised to read my post  Java Multi threaded programming basics before reading this. I try to explain changes from earlier post program here

  1 private final short SIZE = 10;

  2 private boolean isBufferFull = false;

  3 private ReentrantLock lock;

  4 private Condition condition;

Line 3: Instance of ReentrantLock is similar to synchronized keyword locking but it is more intelligent.
Line 4: Condition instance has methods which replaces Object class wait and notify() methods.

  1  public BufferImpl_conc() {

  2     buffer = new CopyOnWriteArrayList<String>();

  3     lock = new ReentrantLock();

  4     condition = lock.newCondition();

  5  }

Line 3 and Line 4: Instantiates lock and condition Objects

 1 private void producesFeed() throws InterruptedException {

 2   lock.lock();

 3    try {

 4      while (true) {

 5         if (isBufferFull) {

 6             System.out.println("Started Consuming!....\n");

 7             condition.signal();

 8             condition.await();

 9         }

 10         buffer.add(String.valueOf(System.nanoTime()));

 11         if (SIZE <= buffer.size()) {

 12           isBufferFull = true;

 13           Thread.sleep(10000);

 14           System.out.println("Buffer full. Production halts...\n");

 15         }

 16       }

 17     } finally {

 18          lock.unlock();

 19     }

 20 }

Line 1: await() at line 8 throws InterruptedException
Line 2: lock.lock() statement is equal to the synchronized(this)  {  . . .  }
Line 7: condition.signal() notifies the waiting thread on same object to start it's execution
Line 8: condition.await() makes current thread to wait on isBufferFull == true condition check
Line 17 to Line 19: lock.unlock() must be called in finally block always

Output:  

Buffer full. Production halts...

Started Consuming!....

Consuming element: 2838231927112595

Consuming element: 2838231927212435

Consuming element: 2838231927229502

Consuming element: 2838231927238888

Consuming element: 2838231927246995

Consuming element: 2838231927254675

Consuming element: 2838231927261075

Consuming element: 2838231927267902

Consuming element: 2838231927274302

Consuming element: 2838231927281555

Started producing!....

Buffer full. Production halts...

Started Consuming!....

Consuming element: 2838242029132348

Consuming element: 2838242029210428

Consuming element: 2838242029244561

Consuming element: 2838242029271015

Consuming element: 2838242029386215

Consuming element: 2838242029448935

Consuming element: 2838242029479228

Consuming element: 2838242029504401

Consuming element: 2838242029529148

Consuming element: 2838242029553895

Started producing!....

Buffer full. Production halts...

Started Consuming!....

Consuming element: 2838252029524881

Consuming element: 2838252029547921

Consuming element: 2838252029556881

Consuming element: 2838252029563281

Consuming element: 2838252029568401

Consuming element: 2838252029573521

Consuming element: 2838252029578215

Consuming element: 2838252029582908

Consuming element: 2838252029588028

Consuming element: 2838252029593148

Started producing!....

Buffer full. Production halts...

Started Consuming!....

Consuming element: 2838262032106639

Consuming element: 2838262032149732

Consuming element: 2838262032165092

Consuming element: 2838262032193252

Consuming element: 2838262032204772

Consuming element: 2838262032214585

Consuming element: 2838262032223972

Consuming element: 2838262032233359

Consuming element: 2838262032241892

Consuming element: 2838262032251279

Started producing!....

Buffer full. Production halts...

Started Consuming!....

Consuming element: 2838272040024285

Consuming element: 2838272040065245

Consuming element: 2838272040077619

Consuming element: 2838272040086152

Consuming element: 2838272040093832

Consuming element: 2838272040101512

Consuming element: 2838272040108766

Consuming element: 2838272040115592

Consuming element: 2838272040122845

Consuming element: 2838272040130099

Started producing!....