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Articles on Trending Technologies
Technical articles with clear explanations and examples
Initialize HashSet in Java
A set is a collection which does not allows duplicate values. HashSet is an implementation of a Set. Following are the ways in which we can initialize a HashSet in Java.Using constructor − Pass a collection to Constructor to initialize an HashSet.Using addAll() − Pass a collection to Collections.addAll() to initialize an HashSet.Using unmodifiableSet() − Pass a collection to Collections.unmodifiableSet() to get a unmodifiable Set.Using add() − Using add(element) method of Set.Following is an example of using above ways.ExampleInfinityNow consider the following code snippet.Exampleimport java.util.Arrays; import java.util.Collections; import java.util.HashSet; import java.util.List; import java.util.Set; public class Tester{ public static ...
Read MoreGet the unqualified name of a class in Java
A qualified class name in Java contains the package that the class originated from. In contrast to this, the unqualified class name contains only the class name without any package information. A program that gets the unqualified name of a class is given as follows:Examplepublic class Demo { public static void main(String[] argv) throws Exception { Class c = java.util.ArrayList.class; String className = c.getName(); System.out.println("The qualified class name is: " + className); if (className.lastIndexOf('.') < 0) { className = className.substring(className.lastIndexOf('.') + 1); ...
Read MoreGet the fully-qualified name of a class in Java
A fully-qualified class name in Java contains the package that the class originated from. An example of this is java.util.ArrayList. The fully-qualified class name can be obtained using the getName() method.A program that demonstrates this is given as follows −Examplepublic class Demo { public static void main(String[] argv) throws Exception { Class c = java.util.ArrayList.class; String className = c.getName(); System.out.println("The fully-qualified name of the class is: " + className); } }OutputThe fully-qualified name of the class is: java.util.ArrayListNow let us understand the above program.The getName() method is used to ...
Read Moreinstanceof operator vs isInstance method in java
isInstance method is equivalent to instanceof operator. The method is used in case of objects are created at runtime using reflection. General practice says if type is to be checked at runtime then use isInstance method otherwise instanceof operator can be used. See the example below −Examplepublic class Tester{ public static void main(String[] args) throws ClassNotFoundException { Integer i = new Integer(10); System.out.println(usingInstanceOf(i)); System.out.println(usingIsInstance(i)); } public static String usingInstanceOf(Object i){ if(i instanceof String){ return "String"; } ...
Read MoreSubtract minutes from current time using Calendar.add() method in Java
Import the following package for Calendar class in Java.import java.util.Calendar;Firstly, create a Calendar object and display the current date and time.Calendar calendar = Calendar.getInstance(); System.out.println("Current Date and Time = " + calendar.getTime());Now, let us decrement the minutes using the calendar.add() method and Calendar.MINUTE constant. Set a negative value since you want to decrease the minutes.calendar.add(Calendar.MINUTE, -15);Exampleimport java.util.Calendar; public class Demo { public static void main(String[] args) { Calendar calendar = Calendar.getInstance(); System.out.println("Current Date = " + calendar.getTime()); // Subtract 15 minutes from current date calendar.add(Calendar.MINUTE, -15); ...
Read MoreUsing reflection to check array type and length in Java
The array type can be checked using the java.lang.Class.getComponentType() method. This method returns the class that represents the component type of the array. The array length can be obtained in int form using the method java.lang.reflect.Array.getLength().A program that demonstrates this is given as follows −Exampleimport java.lang.reflect.Array; public class Demo { public static void main (String args[]) { int[] arr = {6, 1, 9, 3, 7}; Class c = arr.getClass(); if (c.isArray()) { Class arrayType = c.getComponentType(); System.out.println("The array is of type: " ...
Read MoreDisplay Date Time in dd MMM yyyy hh:mm:ss zzz format in Java
Firstly, import the following Java packagesimport java.text.SimpleDateFormat; import java.util.Date;Now, create objectsDate dt = new Date(); SimpleDateFormat dateFormat;Displaying date in the format we want −dateFormat = new SimpleDateFormat("dd MMM yyyy hh:mm:ss zzz");The following is an example −Exampleimport java.text.SimpleDateFormat; import java.util.Date; public class Demo { public static void main(String args[]) { Date dt = new Date(); SimpleDateFormat dateFormat; dateFormat = new SimpleDateFormat("dd MMM yyyy hh:mm:ss zzz"); System.out.println("Date: "+dateFormat.format(dt)); } }OutputDate: 22 Nov 2018 07:53:58 UTC
Read MoreIterator vs forEach in Java
Collections can be iterated easily using two approaches.Using for-Each loop − Use a foreach loop and access the array using object.Using Iterator − Use a foreach loop and access the array using object.DifferencesConcurrentModificationException − Using for-Each loop, if an object is modified, then ConcurrentModificationException can occur. Using iterator, this problem is elliminated.Size Check − Using for-Each, size check is not required. Using iterator if hasNext() is not used properly, NoSuchElementException can occur.Performance − Performance is similar for both cases.Following is an example of using above ways.Exampleimport java.util.ArrayList; import java.util.Iterator; import java.util.List; public class Tester { public static ...
Read MoreC++ Program to Compute Combinations using Factorials
The following is an example to compute combinations using factorials.Example#include using namespace std; int fact(int n) { if (n == 0 || n == 1) return 1; else return n * fact(n - 1); } int main() { int n, r, result; coutn; coutr; result = fact(n) / (fact(r) * fact(n-r)); cout
Read MoreSet a duration in Java
To set a duration, let us declare two objects of Calendar classCalendar c1 = Calendar.getInstance(); Calendar c2 = Calendar.getInstance();Set a time for one of the calendar objectsc2.add(Calendar.HOUR, 9); c2.add(Calendar.MINUTE, 15); c2.add(Calendar.SECOND, 40);Now, find the difference between both the time. One would be the current time and another we declared above −long calcSeconds = (c2.getTimeInMillis() - c1.getTimeInMillis()) / 1000;The following is an example −Exampleimport java.util.Calendar; public class Demo { public static void main(String args[]) { Calendar c1 = Calendar.getInstance(); Calendar c2 = Calendar.getInstance(); // set hour, minute and second c2.add(Calendar.HOUR, 9); ...
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