Install maven on Windows by using "Command Line Prompt"

1.Download maven. http://maven.apache.org/download.cgi (apache-maven-3.3.9-bin.zip)
2. Unzip the file.
3. Open cmd - command line prompt. Set system variable using by below command. (Windows 7 & 8):    

setx M2_HOME "C:\apache-maven-3.3.9"

4. You can see M2_HOME path :

echo %M2_HOME%

5. Update PATH variable. Run the below command in command line prompt:

setx PATH "%PATH%;%M2_HOME%\bin" echo %PATH%

6.Run the below command:

mvn - version

7. Eclipse - maven integration:
         Help - > install new software:   http://download.eclipse.org/technology/m2e/releases/

java.lang.IllegalArgumentException: No enum const class java.util.concurrent.TimeUnit.MİLLİSECONDS

BUG:
I got the below error when i started JBOSS server.
java.lang.IllegalArgumentException: No enum const class java.util.concurrent.TimeUnit.MİLLİSECONDS

FIX:
1. Double click to the server.
2. Click "Open launch configuration"
3. Add to the Vm arguments '-Duser.language=en'
4. Then save and start your server.

ResourceBundle example - read a property file based on the locale inside the class folder

package read.properties.file; import java.util.Locale; import java.util.ResourceBundle; public class ResourcesBundleExample {        public static void main(String[] args) {               ResourceBundle bundle = ResourceBundle.getBundle("config");               // read config_tr_TR.properties               Locale.setDefault(new Locale("tr", "TR"));               bundle = ResourceBundle.getBundle("config");               System.out.println("Current Locale: " + Locale.getDefault());               System.out.println("my name is: " + bundle.getString("who_are_you"));                             // read config_en_US.properties               Locale.setDefault(new Locale("en", "US"));               bundle = ResourceBundle.getBundle("config");               System.out.println("Current Locale: " + Locale.getDefault());               System.out.println("my name is: " + bundle.getString("who_are_you"));        } }

config_tr_TR.properties who_are_you = eda_TR config_en_US.properties who_are_you = eda_EN

outputs:

Current Locale: tr_TR

my name is: eda_TR

Current Locale: en_US

my name is: eda_EN

Read a .properties file inside the class folder

package read.properties.file; import java.io.IOException; import java.io.InputStream; import java.util.Enumeration; import java.util.Properties; public class App {        public static void main(String[] args) {               App app = new App();               app.readProperties();        }        //read a .properties file inside  the class folder        private void readProperties() {               Properties prop = new Properties();               InputStream inputStream = null;               String filename = "config.properties";               try {                      inputStream = getClass().getClassLoader().getResourceAsStream(filename);                      if (inputStream == null) {                            System.out.println("Unable to find " + filename);                            return;                      }                      prop.load(inputStream);                      // get all values                      Enumeration<?> e = prop.propertyNames();                      while (e.hasMoreElements()) {                            String key = (String) e.nextElement();                            String value = prop.getProperty(key);                            System.out.println("Key : " + key + ", Value : " + value);                      }                      // get only one value you wanted                      System.out.println("get only one value you wanted: user: " + prop.getProperty("user"));               } catch (Exception e) {                      // throw or log the exception               } finally {                      if (inputStream != null) {                            try {                                   inputStream.close();                            } catch (IOException e) {                                   // throw or log the exception                            }                      }               }        } }

Config.properties user=eda password=less talk more code

outputs:

Key : user, Value : eda Key : password, Value : less talk more code get only one value you wanted: user: eda

java - Enum as instance variables

public class Test {

    public enum MESSAGE {
        SUCCESS("1"),
        ERROR("2");

        private final String msg_id;

        private MESSAGE( final String msg_id ) {
            this.msg_id = msg_id;
        }

        public String getMsgId() {
             return msg_id;
        }
    }

    public static void main(String[] args) {
        System.out.println("MESSAGE.ERROR --> " + MESSAGE.ERROR.getMsgId());
    }

}

Java singleton design pattern example

//Singleton design pattern - example class //Eager initialization public class SingletonObject {             //Our static variable holding an instance of an existing singleton class        private static SingletonObject singletonObject;              static {          // Initialize "singletonObject" only once          singletonObject = new SingletonObject();        }             //The class constructor method is also private. We can not create the class instance outside of this class        private SingletonObject() {               //...constructor codes        }             //The method that returns the single instance of the SingletonObject class        public static SingletonObject getInstance() {               return singletonObject;        }        //Prevent cloning of class by throwing CloneNotSupportedException        @Override        public Object clone() throws CloneNotSupportedException {               throw new CloneNotSupportedException();        } }

//Singleton design pattern - example class //Lazy initialization public class SingletonObject {             //Our static variable holding an instance of an existing singleton class        private static SingletonObject singletonObject = null;              //The class constructor method is also private. We can not create the class instance outside of this class        private SingletonObject() {               //...constructor codes        }             //The method that returns the single instance of the SingletonObject class        public static SingletonObject getInstance() {           if(singletonObject == null) {                  synchronized (SingletonObject.class) {                         //double-checked locking                         if(singletonObject == null) {                               singletonObject = new SingletonObject();                         }                  }                             }               return singletonObject;        }        //Prevent cloning of class by throwing CloneNotSupportedException        @Override        public Object clone() throws CloneNotSupportedException {               throw new CloneNotSupportedException();        } }

Java builder design pattern example

import java.util.List; public class Student {     private String name;     private int age;               //optional     private List<String> language; //optinal     public static class Builder {         private String name;         private int age;         private List<String> language;         public Builder (String name) {             this.name = name;         }         public Builder age(int age) {             this.age = age;             return this;         }         public Builder language(List<String> language) {             this.language = language;             return this;         }         public Student build() {             return new Student(this);         }     }     private Student(Builder builder) {         name = builder.name;         age = builder.age;         language = builder.language;     }     @Override     public String toString() {         return "Student{" + "name='" + name + '\'' + ", age=" + age + ", language=" + language +'}';     } }

import java.util.Arrays; public class TestStudent {     public static void main(String[] args) {        Student s1 = new Student.Builder("eda").build();                Student s2 = new Student.Builder("eda").age(28).language(Arrays.asList("japanese","english")).build();         System.out.println("s1--> " + s1);         System.out.println("s2--> " + s2);     } }

Output:

s1--> Student{name='eda', age=0, language=null}

s2--> Student{name='eda', age=28, language=[japanese, english]}


Quoting from Joshua Bloch's Second Edition of Effective Java:
"In summary, the Builder pattern is a good choice when designing classes
whose constructors or static factories would have more than a handful of
parameters, especially if most of those parameters are optional."