Initializing a boolean array in java with an example program

Posted by: Instanceofjava Posted date: 9:27 PM / comment : 0 ,

  • Initializing a boolean variable : boolean b=true;
  • In some cases we need to initialize all values of boolean array with true or false.
  • In such cases we can use Arrays.fill() method
  • Arrays.fill(array, Boolean.FALSE);
  • java initialize boolean array with true:  Arrays.fill(array, Boolean.FALSE);
  • Lets see an example java program on how to assign or initialize boolean array with false or true values.



#1: Java Example program on initializing boolean array.

  1. package com.instanceofjava;

  3. import java.util.Arrays;
  4. /**
  5.  * @author www.Instanceofjava.com
  6.  * @category interview questions
  7.  * 
  8.  * Description: Initialize boolean array values with false or true
  9.  *
  10.  */
  11. public class InitializeBoolean {

  13. public static void main(String[] args) {
  15. Boolean[] array = new Boolean[4];
  16. //initially all values will be null
  17. for (int i = 0; i < array.length; i++) {
  18. System.out.println(array[i]);
  19. }
  20. Arrays.fill(array, Boolean.FALSE);
  21. // all values will be false
  22. for (int i = 0; i < array.length; i++) {
  23. System.out.println(array[i]);
  24. }
  26. Arrays.fill(array, Boolean.TRUE);
  27. // all values will be false
  28. for (int i = 0; i < array.length; i++) {
  29. System.out.println(array[i]);
  30. }
  31. }

  33. }

Output:

  1. null
  2. null
  3. null
  4. null
  5. false
  6. false
  7. false
  8. false
  9. true
  10. true
  11. true
  12. true


java initialize boolean array with true

Java 8 initialize set with values with an example program

Posted by: Instanceofjava Posted date: 9:05 PM / comment : 0 ,

  • We can initialize set while defining by passing values to constructor.
  • For example to initialize HashSet we can use Arrays.asList(value1,value2).
  • Set<Integer> hashset = new HashSet<>(Arrays.asList(12, 13));

#1: Java Example program to initialize set without using java 8

  1. import java.util.Arrays;
  2. import java.util.HashSet;
  3. import java.util.Set;
  4. /**
  5.  * @author www.Instanceofjava.com
  6.  * @category interview questions
  7.  * 
  8.  * Description: Initialize set 
  9.  *
  10.  */
  11. public class InitializeSet {

  13. public static void main(String[] args) {

  15. Set<Integer> hashset = new HashSet<>(Arrays.asList(12, 13));
  16. System.out.println(hashset);
  17. }

  19. }

Output:

  1. [12, 13]


  • We can initialize set in java 8 using Stream.
  • Stream.of("initialize", "set").collect(Collectors.toSet());



#2: Java Example program to initialize set without using java 8

  2. import java.util.Set;
  3. import java.util.stream.Collectors;
  4. import java.util.stream.Stream;
  5. /**
  6.  * @author www.Instanceofjava.com
  7.  * @category interview questions
  8.  * 
  9.  * Description: Initialize set using java 8 Stream
  10.  *
  11.  */
  12. public class InitializeSet {

  14. public static void main(String[] args) {

  16. Set<String> set = Stream.of("initialize", "set").collect(Collectors.toSet());
  17. System.out.println(set);
  18. }

  20. }



Output:

  1. [set, initialize]


  • We can initialize Set in java 8 by creating stream from an Array and list


#3: Java Example program to initialize set without using java 8


java 8 initialize set with values with an example program

Top 10 Java array example programs with output

Posted by: Instanceofjava Posted date: 11:23 PM / comment : 0

1.Java Example program to find missing numbers in an array.
2. Java interview Example program to find second maximum number in an integer array


3.Java Practice programs on arrays: find second smallest number.


4. How many ways we can print arrays in java: lets check below link for 5 different ways.


5.Advantages and disadvantages of arrays




6. Benefits of arraylist over arrays


7. Creating Array of objects in java 


8. Find top two maximum numbers in an array : java array practice programs


9. Remove duplicates from an array java


10. Sort integer array using Bubble Sort in java


How to run multiple java programs simultaneously in eclipse

Posted by: Instanceofjava Posted date: 10:30 PM / comment : 0

  • In some cases we may need to run two java programs simultaneously and need to observe the ouput of two progarsms. In such cases we need to run multiple java programs parallel.  
  • Now we will see how to run two java programs simultaneously
  • First thing we need to understand is we can run multiple java programs at a time in eclipse.
  • Second thing is we can view multiple consoles in eclipse.   



#1. How can we open multiple consoles in eclipse?

  • In Eclipse console window right side we will have one rectangular box with Plus symbol on it to open a new console. by clicking on it we can open a new console view.

open multiple consoles view in eclipse


2: Create two java programs.

ClassOne:
  1. package com.instanceofjava;

  3. public class ClassOne {
  4. /**
  5. * @author www.Instanceofjava.com
  6. * @category interview questions
  7. * 
  8. * Description: how to run two java programs simultaneously
  9. *
  10. */
  11. public static void main(String[] args) throws InterruptedException {

  13. for (int i = 0; i < 100; i++) {
  14. Thread.sleep(1000);
  15. System.out.println(i);
  16. }
  17. }
  18. }

 ClassTwo
  1. package System.out;

  3. public class ClassTwo {
  4. /**
  5. * @author www.Instanceofjava.com
  6. * @category interview questions
  7. * 
  8. * Description: how to run two java programs simultaneously
  9. *
  10. */
  11. public static void main(String[] args) throws InterruptedException {
  12. for (int i = 100; i < 200; i++) {
  13. System.out.println(i);
  14. Thread.sleep(1000);
  15. }


  18. }

  20. }


  • Run ClassOne and ClassTwo.
  • Pin console.

pin console.png



  • You can see both the running programs with output with different console views.
how to run two java programs simultaneously

Log4j example in java using properties file

Posted by: Instanceofjava Posted date: 11:31 PM / comment : 0

  • Logging is very important part of programming. Logging helps programmer to understand process flow and identify the problems where actually occurred.
  • Log4J will be configured externally using properties file. We can print the logging statements in the console or we can push them in to a log file based on the requirement.
  •  org.apache.log4j class will provide required classes to implement logging
  • We need to add Log4J dependency in our project.
  • Create instance of logger by using Logger.getLogger(Log4JExample.class);
  • Lets see how to create log4j.properties file in eclipse



1. Create a maven project and add Log4J dependency:


how to create log4j.properties file in eclipse

2. Create log4j.properties file


log4j.properties example file

  1. log4j.rootLogger=INFO, console

  3. log4j.appender.console=org.apache.log4j.ConsoleAppender

  5. log4j.appender.console.layout=org.apache.log4j.PatternLayout
  6. log4j.appender.console.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss.SSS zzz}

3.Create java example program to read log4j.properties file

  1. import org.apache.log4j.BasicConfigurator;
  2. import org.apache.log4j.Logger;

  4. public class Log4JExample {

  6. static Logger logger = Logger.getLogger(Log4JExample.class);
  7.     public static void main(String[] args)
  8.     {
  9.     BasicConfigurator.configure();
  10.     logger.info("main method start!!");
  11.    
  12.     System.out.println("hi");
  13.     logger.info("log4j properties configuration example");
  14.      
  15.     logger.info("main method end!!");
  16.     }
  17. }

Output:

  1. 2018-02-08 23:09:10.747 IST0 [main] INFO Log4JExample  - main method start!!
  2. hi
  3. 2018-02-08 23:09:10.752 IST5 [main] INFO Log4JExample  - log4j properties configuration example
  4. 2018-02-08 23:09:10.753 IST6 [main] INFO Log4JExample  - main method end!!

Java program to reverse ArrayList elements

Posted by: Instanceofjava Posted date: 11:41 PM / comment : 0

  • How to reverse an ArrayList in java.
  • By using Collections.reverse() method we can reverse ArrayList in java.



#1: Java Example program to reverse ArrayList 

  1. package com.instanceofjava;

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

  6. public class ReverseArrayList {
  7. /**
  8. * @author www.Instanceofjava.com
  9. * @category interview questions
  10. * 
  11. * Description: Java Example program to reverse an ArrayList
  12. *
  13. */
  14. public static void main(String[] args) {
  16. ArrayList<String> arrayList= new ArrayList<>();
  17. arrayList.add("Apple");
  18. arrayList.add("Banana");
  19. arrayList.add("Orange");
  20. Collections.reverse(arrayList);
  22. System.out.println(arrayList);
  24. }

  26. }


Output:

  1. [Orange, Banana, Apple]


#2: Java Example program to print arraylist in reverse order 


reverse arraylist in java example program

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