Java Program to convert ArrayList to String array

Posted by: Instanceofjava Posted date: February 05, 2018 / comment : 0 , ,

  • Java code to convert arraylist to string array.
  • We can convert ArrayList of strings to String array by using  toArray() method.
  • Lets see an Example java program to convert ArrayList to string array.



#1:  Java example program to convert ArrayList to String Array

  1. package com.instanceofjava;

  3. import java.util.ArrayList;
  4. import java.util.List;

  6. public class ArrayListToStringArray {
  7. /**
  8. * @author www.Instanceofjava.com
  9. * @category interview programs
  10. * 
  11. * Description: Java Prorgam to convert ArrayList to String array
  12. *
  13. */
  14. public static void main(String[] args) {
  16. List<String> lstflowers = new ArrayList<String>();
  17. lstflowers.add("Rose");
  18. lstflowers.add("Lilly");

  20. String[] arrayflower = new String[lstflowers.size()];
  21. arrayflower = lstflowers.toArray(arrayflower);

  23. for(String flower : arrayflower)
  24.     System.out.println(flower);
  25. }

  27. }


Output:


  1. Rose
  2. Lilly

#2:  Java example program to convert ArrayList to String Array Using java 8

  1. package com.instanceofjava;

  3. import java.util.ArrayList;
  4. import java.util.List;

  6. public class ArrayListToStringArray {
  7. /**
  8. * @author www.Instanceofjava.com
  9. * @category interview programs
  10. * 
  11. * Description: Java Prorgam to convert ArrayList to String array using java 8
  12. *
  13. */
  14. public static void main(String[] args) {
  16. List<String> lstflowers = new ArrayList<String>();
  17. lstflowers.add("Rose");
  18. lstflowers.add("Lilly");

  20. String[] arrayflower = lstflowers.toArray(new String[lstflowers.size()]);

  22. for(String flower : arrayflower)
  23.     System.out.println(flower);
  24. }

  26. }


java program to convert arraylist to string array

Java 8 subtract N minutes from current date

Posted by: Instanceofjava Posted date: February 05, 2018 / comment : 0 ,

  • Java 8 provides java.time.LocalDateTime class.
  • By using minusMinutes() methods of LocalDateTime class we can subtract minutes from date or current date in java.
  • Lets see an example program on how to remove / subtract n minutes from current date using java 8.



  1. package com.instanceofjava.java8;
  2. import java.time.LocalDateTime;

  4. /**
  5.  * @author www.Instanceofjava.com
  6.  * @category interview programs
  7.  * 
  8.  * Description: subtract minutes to current date using java 8
  9.  *
  10.  */
  11. public class AddMinutesToDate {

  13. public static void main(String[] args) {
  15. //create data using java 8 LocalDateTime 
  16.     LocalDateTime datetime= LocalDateTime.now();
  18. System.out.println("Before subtracting 30 minutes to date: "+datetime);
  19.     //add seconds by using minuesMinutes(seconds) method
  20. datetime=datetime.minusMinutes(30);
  21. System.out.println("After subtracting 30 minutes to date: "+datetime);

  23. }

  25. }

Output:

  1. Before subtracting 30 minutes to date: 2018-02-05T22:41:42.463
  2. After subtracting 30 minutes to date: 2018-02-05T22:11:42.463


subtract minutes from java 8 date time.png

How to Add N minutes to current date using java 8

Posted by: Instanceofjava Posted date: February 05, 2018 / comment : 0 ,

  • Java 8 providing java java.time package which is having more utility methods related to date and time.
  • LocalDateTime class providing plusMinutes(int minutes) method to add minutes to current date or given date in java.
  • Lets see an example program to add 30 minutes to current date using java 8 LocalDateTime class.



#1: Java Example program to add 30 minutes to current date 

  1. package com.instanceofjava.java8;

  3. import java.time.LocalDateTime;

  5. /**
  6.  * @author www.Instanceofjava.com
  7.  * @category interview programs
  8.  * 
  9.  * Description: Add minutes to current date using java 8
  10.  *
  11.  */
  12. public class AddMinutesToDate {

  14. public static void main(String[] args) {
  16. //create data using java 8 LocalDateTime 
  17.     LocalDateTime datetime= LocalDateTime.now();
  19. System.out.println("Before adding minutes to date: "+datetime);
  20.     //add seconds by using plusMinutes(Minutes) method
  21. datetime=datetime.plusMinutes(30);
  22. System.out.println("After adding 30 minutes to date: "+datetime);

  24. }

  26. }

Output:


  2. Before adding minutes to date: 2018-02-05T22:14:33.664
  3. After adding 30 minutes to date: 2018-02-05T22:44:33.664



add minutes to current date java 8


Can we define default methods in functional interfaces in java 8

Posted by: Instanceofjava Posted date: February 05, 2018 / comment : 0 ,

  • Functional interfaces in java 8 will have single abstract method in it.
  • Check below two pages regarding defining and using functional interfaces using Lamda expressions.
  • Java 8 functional interface with example
  • Implement java 8 functional interface using lambda example program
  • We can define default methods in functional interfaces in java 8.
  • But every functional interface must have single abstract method in it.
  • As we know that default methods should have a implementation as they are not abstract methods.
  • Lets see an example program on defining functional interface with default method.



#1:  Java example program to create functional interface with default method.

  1. package com.instanceofjava.java8;

  3. /**
  4.  * @author www.Instanceofjava.com
  5.  * @category interview programming questions
  6.  * 
  7.  * Description: java 8 functional interfaces
  8.  *
  9.  */
  10. @FunctionalInterface
  11. public interface FunctionalInterfaceExample {
  12.  
  13. void show();
  14.         //default method
  15. default void message() {
  16. System.out.println("hello this is default method in functional interface");
  17. }
  18. }


#2: Java Example program on how to implement functional interface abstract method and use default method.


Can we define default methods in functional interfaces in java 8


Functional interface with multiple methods in java 8

Posted by: Instanceofjava Posted date: February 04, 2018 / comment : 0 ,

  • Functional interfaces will contains single abstract method with @FunctionalInterface annotation.
  • Check below two posts for defining functional interface and implementing functional interface method using Lamda in java 8.
  • Java 8 functional interface with example
  • Implement java 8 functional interface using lambda example program
  • Now the question is can we declare or define multiple abstract methods in one functional interface in java 8.
  • No. Functional interface should contain only one abstract method so that Lamda will implement it.
  • Lets see what happens if we define multiple abstract methods inside a functional interface
  • Note: all methods inside any interface by default abstract methods.



  1. package com.instanceofjava.java8;

  3. /**
  4.  * @author www.Instanceofjava.com
  5.  * @category interview programming questions
  6.  * 
  7.  * Description: java 8 functional interfaces
  8.  *
  9.  */
  10. @FunctionalInterface
  11. public interface FunctionalInterfaceExample {
  12. //compile time error: Invalid '@FunctionalInterface' annotation; FunctionalInterfaceExample is
  13. not a functional interface
  14.  
  15. void show();
  16. void calculate();
  17. }


  • If we define multiple abstract methods inside a functional interface it will throw a compile time error.
  • Invalid '@FunctionalInterface' annotation; FunctionalInterfaceExample is not a functional interface

Implement java 8 functional interface using lambda example program

Posted by: Instanceofjava Posted date: February 04, 2018 / comment : 0 ,

  • Functional interfaces introduces in java 8 .
  • Functional interfaces will have single abstract method in it.
  • Check here for full details on Java 8 functional interface with example.
  • Functional interfaces will be implemented by java 8 Lamda expressions.
  • Lets see an example program on how can we use functional interfaces or how can we implement functional interfaces using Lamda expression in java 8.
  • Create one functional interface with one abstract method in it.
  • Create a class and implement this abstract method using Lamda Expressions.



#1: Java example program to create functional interface.

functional interface example in java 8 using lamda expressions


#2: Java example program to implement functional interface using Lamda expressions in java 8.

  2. package com.instanceofjava.java8;
  3. /**
  4.  * @author www.Instanceofjava.com
  5.  * @category interview programming questions
  6.  * 
  7.  * Description: java 8 Lamda expressions
  8.  *
  9.  */
  10. public class LamdaExpressions {

  12. public static void main(String[] args) {
  14. FunctionalInterfaceExample obj = ()->{
  15. System.out.println("hello world");
  16. };

  18. obj.show();
  19. }

  21. }

Output:

  2. hello world

Java 8 functional interface with example

Posted by: Instanceofjava Posted date: February 04, 2018 / comment : 0 ,

  • Java 8 introduced Lamda expressions and functional interfaces.
  • An interface with one abstract method is known as functional interfaces.
  • Functional interfaces in java 8 marked with @FunctionalInterface.
  • These functional interfaces implementation will be provided by Lamda expressions.
  • Default methods in java 8 interfaces are not abstract methods. But we can define  multiple default methods in functional interface.
  • Java 8 functional interface example program


#1: Java Example program to create java 8 functional interface.


  1. package com.instanceofjava.java8;

  3. /**
  4.  * @author www.Instanceofjava.com
  5.  * @category interview programming questions
  6.  * 
  7.  * Description: java 8 functional interfaces
  8.  *
  9.  */
  10. @FunctionalInterface
  11. public interface FunctionalInterfaceExample {

  13. void show();
  14. }


  • Can we create functional interface with @FunctionalInterface annotation without any single abstract method?
  • No. Functional interfaces must have single abstract method inside it.
  • It will throw compile time error : Invalid '@FunctionalInterface' annotation; FunctionalInterfaceExample is not a functional interface.
  • Lets see an example program on this so that we can conclude it.
  • How to use these functional interfaces we will discuss in next post on Lamda expressions.
  • Implement java 8 functional interface using lambda example program


#2: What will happend if we define functional interface without a single abstract method in it?

functional interface example in java 8
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