Learn Java by Examples: October 2013

How to create Composite Primary Keys by @Embeddable annotation in Hibernate using JPA ?

Program to demonstrate how to create Composite Primary Keys by @Embeddable annotation in Hibernate using JPA.

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How to create Composite Primary Keys by @EmbeddedId annotation in Hibernate using JPA ?

Program to demonstrate how to create Composite Primary Keys by @EmbeddedId annotation in Hibernate using JPA.

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How to Create - Store - Save - Persist a Java Entity Object in Hibernate using JPA ?.

Program to demonstrate how to Create - Store - Save - Persist a Java Entity Object in Hibernate using JPA.

How to create Composite Primary Keys by @IdClass annotation in Hibernate using JPA ?

Program to demonstrate how to create Composite Primary Keys by @IdClass annotation in Hibernate using JPA.

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How to implement Component Mapping by @Embedded annotation in Hibernate using JPA ?.

Program to demonstrate how to implement Component Mapping by @Embedded annotation in Hibernate using JPA.

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How to update a detached Entity by merge method in Hibernate using JPA ?.

Program to demonstrate how to update a detached Entity by merge method in Hibernate using JPA.

How to delete a Java Entity by its primary key in Hibernate using JPA ?

Program to demonstrate how to delete a Java Entity by its primary key in Hibernate using JPA.

How to create persistence xml file in Hibernate using JPA ?.

A simple video explaining persistence.xml file in JPA.

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How to convert a Java Object into an Entity in Hibernate using JPA ?.

A simple video explaining Entities creation in Hibernate using JPA.

How to calculate Exponential of a number in Java using Math class ?.

Program to demonstrate how to calculate Exponential of a number in Java using Math class.

How to declare or make a Java method, class and fields as Deprecated ?.

Program to demonstrate how to declare or make a Java method, class and fields as Deprecated.

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@Deprecated
public class Calculator {
 
 @Deprecated
 public int sum(int x , int y){
  return x + y;
 }
 
 public int sum(int ... numbers) {
  int sum = 0;
  for(int number : numbers) {
   sum = sum + number;
  }
  return sum;
 }
 
 public static void main(String [] args) { 
  Calculator calculator = new Calculator();
  int result = calculator.sum(5, 10);
  System.out.println("The sum is : " + result);
  
  result = calculator.sum(5, 5, 10, 15);
  System.out.println("The sum is : " + result);
  
 }
 
}

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How to use Javadoc Comments in Java program for Documentation ?.

Program to demonstrate how to use Javadoc Comments in Java program for Documentation.

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/** 
 * This class demonstrate usage of javadoc comments.
 * 
 * @author Jonty.
 */
public class JavadocDemo {

	/**
	 *  
	 * @param number1 first int value
	 * @param number2 second int value
	 * @return sum of number1 and number2
	 * @throws no exception
	 */
	public int sum(int number1 , int number2) {
		return number1 + number2;
	}

}

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How to query Environment Variables through a Java Program ?.

Program to demonstrate how to query Environment Variables through Java.

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import java.util.Map;
import java.util.Scanner;


public class EnvironmentVariables {

 public static void main(String[] args) {
  
  Scanner scanner = new Scanner(System.in);
  
  System.out.print("Enter the name of Environment Variables : ");
  
  String name = scanner.nextLine();
  
  String value = System.getenv(name);
  
  System.out.println(name + " = " + value);
  
  Map < String , String > mapOfEnvironmentVariables = System.getenv();
  
  for(String var : mapOfEnvironmentVariables.keySet()) { 
   
   System.out.println(var + " = " + System.getenv(var));
   
  }  

 }

}

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Output of the program :

How to use Command Line Arguments in Java ?.

Program to demonstrate how to use Command Line Arguments in Java.

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public class CommandLineArguments {

 public static void main(String[] args) {
  
  System.out.print(args[0] + " ");
  
  System.out.print(args[1]);
  

 }

}

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Output of the program :

hello world

How to create a file in Java ?

Program to demonstrate how to create a file in Java.

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import java.io.File;
import java.io.IOException;

public class CreateFile {

 public static void main(String[] args) {
  
  File file = new File("test.txt");
  
  try {
  
  if(file.createNewFile()) { 
   System.out.println("File successfully created.");
  } else {
   System.out.println("File already exists.");
  }
  
  } catch(IOException ioe) { 
   System.out.println("IO Exception occured.");
  }

 }

}

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