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Object Oriented Programming Articles
Page 253 of 589
Java Program to insert a value to a SortedSet
Let’s say we have the following SortedSet −SortedSet set = new TreeSet(); set.add("T"); set.add("R"); set.add("S"); set.add("Q"); set.add("V"); set.add("U"); set.add("W");Now, after displaying the above elements with Iterator, you can insert values like this to a SortedSetset.add("Z"); set.add("Y");Exampleimport java.util.Iterator; import java.util.SortedSet; import java.util.TreeSet; public class Demo { public static void main(String[] argv) throws Exception { SortedSet set = new TreeSet(); set.add("T"); set.add("R"); set.add("S"); set.add("Q"); set.add("V"); set.add("U"); set.add("W"); Iterator i = set.iterator(); ...
Read MoreChecking if a HashSet contains certain value in Java
Let’s say the following is our Integer array −Integer arr[] = { 50, 100, 150, 200, 250, 300 };Set the above integer array in HashSet −Setset = new HashSet(Arrays.asList(arr));Now, let us check whether the HashSet contains certain value or not −set.contains(150)TRUE is returned if the value is in the List, else FALSE is the return value.Exampleimport java.util.Arrays; import java.util.HashSet; import java.util.Set; public class Demo { public static void main(String[] a) { Integer arr[] = { 50, 100, 150, 200, 250, 300 }; Setset = new HashSet(Arrays.asList(arr)); System.out.println(set.contains(200)); ...
Read MoreMake a Hashtable read-only in Java
Read-only Hashtable would mean users won’t be able to add or remove elements from it. Let us first create a Hashtable with key-value pair −Hashtablehash = new Hashtable(); hash.put("1", "A"); hash.put("2", "B"); hash.put("3", "C"); hash.put("4", "D"); hash.put("5", "E"); hash.put("6", "F"); hash.put("7", "G");Now, use unmodifiableMap() to form a Hashtable read-only −Mapm = Collections.unmodifiableMap(hash);Exampleimport java.util.Collections; import java.util.Hashtable; import java.util.Map; public class Demo { public static void main(String[] s) { Hashtablehash = new Hashtable(); hash.put("1", "A"); hash.put("2", "B"); hash.put("3", "C"); hash.put("4", "D"); hash.put("5", "E"); ...
Read MoreJava Program to get the reverse of the NavigableSet
We will create a NavigableSet collection and add some elements −NavigableSet set = new TreeSet(); set.add("ABC"); set.add("DEF"); set.add("GHI"); set.add("JKL"); set.add("MNO"); set.add("PQR"); set.add("STU");Now, use descendingSet() for the reverse of NavigableSet −NavigableSetreverse = set.descendingSet();Exampleimport java.util.NavigableSet; import java.util.TreeSet; public class Demo { public static void main(String[] args) { NavigableSet set = new TreeSet(); set.add("ABC"); set.add("DEF"); set.add("GHI"); set.add("JKL"); set.add("MNO"); set.add("PQR"); set.add("STU"); NavigableSetreverse = set.descendingSet(); System.out.println("NavigableSet = " + set); System.out.println("NavigableSet ...
Read MoreJava Program to get day of week for the last day of each month in 2019
For last day of each month, at first create a List collection for day of week −ListdayOfWeek = new ArrayList();Now, get day of week for the last day of each month in 2019, set the year using withYear() and use lastDayOfMonth() and getDayOfWeek methods −for (Month m: Month.values()) { DayOfWeek days = LocalDate.now().withYear(2019).with(m).with(TemporalAdjusters.lastDayOfMonth()).getDayOfWeek(); }Exampleimport java.time.DayOfWeek; import java.time.LocalDate; import java.time.Month; import java.time.temporal.TemporalAdjusters; import java.util.ArrayList; import java.util.List; public class Demo { public static void main(String[] argv) { ListdayOfWeek = new ArrayList(); for (Month m: Month.values()) { DayOfWeek days = LocalDate.now().withYear(2019).with(m).with(TemporalAdjusters.lastDayOfMonth()).getDayOfWeek(); ...
Read MoreJava Program to fill an array with random numbers
Let us first crate an array −double[] arr = new double[5];Now, create Random class object −Random randNum = new Random();Now, fill the above array with random numbers −for (int i = 0; i < 5; i++) { arr[i] = randNum.nextInt(); }Exampleimport java.util.Arrays; import java.util.Random; public class Demo { public static void main(String args[]) { double[] arr = new double[5]; Random randNum = new Random(); for (int i = 0; i < 5; i++) { arr[i] = randNum.nextInt(); } System.out.println("Random numbers = "+Arrays.toString(arr)); } }OutputRandom numbers = [-6.59888981E8, 1.141160731E9, -9.931249E8, 1.335266582E9, 8.27918412E8]
Read MoreIs it possible to use this keyword in static context in java?
A static method or, block belongs to the class and these will be loaded into the memory along with the class. You can invoke static methods without creating an object. (using the class name as reference).Whereas "this" in Java acts as a reference to the current object. But static contexts(methods and blocks) doesn't have any instance they belong to the class.In a simple sense, to use “this” the method should be invoked by an object, which is not always necessary with static methods.Therefore, you cannot use this keyword from a static method.ExampleIn the following Java program, the class ThisExample contains a private ...
Read MoreCan we declare final variables without initialization in java?
In Java, final is the access modifier which can be used with a filed class and a method.When a method if final it cannot be overridden.When a variable is final its value cannot be modified further.When a class is final it cannot be extended.Declaring final variable without initializationIf you declare a final variable later on you cannot modify or, assign values to it. Moreover, like instance variables, final variables will not be initialized with default values.Therefore, it is mandatory to initialize final variables once you declare them.Still, if you try to declare final variables without initialization that will generate a ...
Read MoreWhy main() method must be static in java?
Static − If you declare a method, subclass, block, or a variable static it is loaded along with the class.In Java whenever we need to call an (instance) method we should instantiate the class (containing it) and call it. If we need to call a method without instantiation it should be static. Moreover, static methods are loaded into the memory along with the class.In the case of the main method, it is invoked by the JVM directly, so it is not possible to call it by instantiating its class. And, it should be loaded into the memory along with the ...
Read MoreCan we declare main() method as private or protected or with no access modifier in java?
Java provides various access specifiers namely private, public and protected etc...The Private modifier restricts the access of members from outside the class. A class and interface cannot be public.The Public access modifier can be associated with class, method, constructor, interface, etc. public can be accessed from any other class.The protected access modifier can be associated with variables, methods, and constructors, which are declared protected in a superclass can be accessed only by the subclasses in other package or any class within the package of the protected members' class.The default access modifier does not have keyword a variable or method declared ...
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