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Object Oriented Programming Articles
Page 250 of 589
How to extract multiple integers from a String in Java?
Let’s say the following is our string with integer and characters −String str = "(29, 12; 29, ) (45, 67; 78, 80)";Now, to extract integers, we will be using the following pattern −\dWe have set it with Pattern class −Matcher matcher = Pattern.compile("\d+").matcher(str);Exampleimport java.util.ArrayList; import java.util.List; import java.util.regex.Matcher; import java.util.regex.Pattern; public class Demo { public static void main(String[] args) { String str = "(29, 12; 29, ) (45, 67; 78, 80)"; Matcher matcher = Pattern.compile("\d+").matcher(str); Listlist = new ArrayList(); while(matcher.find()) { list.add(Integer.parseInt(matcher.group())); } System.out.println("Integers = "+list); } }OutputIntegers = [29, 12, 29, 45, 67, 78, 80]
Read MoreHow to get the Checksum of a Byte Array in Java?
Create a Byte Array for which you want the Checksum −byte[] arr = "This is it!".getBytes();Now, create a Checksum object −Checksum checksum = new Adler32(); checksum.update(arr, 0, arr.length);The update() above updates the current checksum with the specified array of bytes.Now, get the checksum with getValue() method, which gives the current checksum value.Exampleimport java.util.zip.Adler32; import java.util.zip.Checksum; public class Demo { public static void main(String[] argv) throws Exception { byte[] arr = "This is it!".getBytes(); Checksum checksum = new Adler32(); checksum.update(arr, 0, arr.length); long res = checksum.getValue(); ...
Read MoreJava Program to change a file attribute to writable
Let’s say our file is “input.txt”, which is set read-only −File myFile = new File("input.txt"); myFile.createNewFile(); myFile.setReadOnly();Now, set the above file to writable −myFile.setWritable(true);After that, you can use canWrite() to check whether the file is writable or not.Exampleimport java.io.File; public class Demo { public static void main(String[] args) throws Exception { File myFile = new File("input.txt"); myFile.createNewFile(); myFile.setReadOnly(); if (myFile.canWrite()) { System.out.println("Writable!"); } else { System.out.println("Read only mode!"); } // ...
Read MoreCheck the frequency of an element in Java with Collections.frequency
Create a List in Java −List< String >list = Arrays.asList("P", "Q", "R", "P", "T", "P", "U", "V", "W", "X", "W" );Now, let’s say you want to get the frequency of element P. For that, use the Collections.frequency() method −Collections.frequency(list, "P");A shown above, we can find the occurrence of any letter as well −Collections.frequency(list, "T");Exampleimport java.util.Arrays; import java.util.Collections; import java.util.List; public class Demo { public static void main(String[] args) { Listlist = Arrays.asList("P", "Q", "R", "P", "T", "P", "U", "V", "W", "X", "W" ); int checkOccurrence = Collections.frequency(list, "P"); System.out.println("Occurrence of ...
Read MoreHow to create a Queue from LinkedList in Java?
Let us create a queue from LinkedList like this −Queuequeue = new LinkedList(); queue.add("P"); queue.add("Q"); queue.add("R"); queue.add("S"); queue.add("T"); queue.add("U"); queue.add("V");Now, use a List to display the elements of the queue −Listlist = new ArrayList(queue);Exampleimport java.util.ArrayList; import java.util.LinkedList; import java.util.List; import java.util.Queue; public class Demo { public static void main(String[] args) { Queuequeue = new LinkedList(); queue.add("P"); queue.add("Q"); queue.add("R"); queue.add("S"); queue.add("T"); queue.add("U"); queue.add("V"); Listlist = new ArrayList(queue); for (Object ob: ...
Read MoreJava Program to create a new list with values from existing list with Function Mapper
To create a new list with values from fields from existing list with Function Mapper, the following is an example. Here, we have a class Employee −class Employee { private String emp_name; private int emp_age; private String emp_zone; }The following is an example that creates a new list from existing with Function Mapper −Exampleimport java.util.ArrayList; import java.util.Arrays; import java.util.List; import java.util.function.Function; public class Demo { public static void main(String args[]) { List < Employee > emp = Arrays.asList(new Employee("Jack", 29, "South"), new Employee("Tom", 24, "North"), new Employee("Harry", 35, "West"), ...
Read MoreHow to create Java Priority Queue to ignore duplicates?
The simplest way to create a Java Priority Queue to ignore duplicates is to first create a Set implementation −HashSet set = new HashSet (); set.add(100); set.add(150); set.add(250); set.add(300); set.add(250); set.add(500); set.add(600); set.add(500); set.add(900);Now, create Priority Queue and include the set to remove duplicates in the above set −PriorityQueuequeue = new PriorityQueue(set);Exampleimport java.util.HashSet; import java.util.PriorityQueue; public class Demo { public static void main(String[] args) { HashSetset = new HashSet(); set.add(100); set.add(150); set.add(250); set.add(300); set.add(250); set.add(500); ...
Read MoreHow to fetch elements with iterator in Java?
Let us first create a List and add elements −Listlist = Arrays.asList(new String[] { "P", "Q", "R", "S", "T", "U", "V", "W" });Now, use Iterator to fetch each element −Iteratori = list.iterator();Display the elements −while (i.hasNext()) { System.out.println(i.next()); }Exampleimport java.util.Arrays; import java.util.Iterator; import java.util.List; public class Demo { public static void main(String[] a) { Listlist = Arrays.asList(new String[] { "P", "Q", "R", "S", "T", "U", "V", "W" }); Iteratori = list.iterator(); System.out.println("Displaying elements..."); while (i.hasNext()) { System.out.println(i.next()); } ...
Read MoreJava Program to get previous and next index using ListIterator
To get the exact evaluation of the previous and next index, you need use the next() method of the Iterator. This will eventually help you in gaining more understanding about Iterators. Let us first create an ArrayList and add some elements −ArrayList arrList = new ArrayList (); arrList.add(100); arrList.add(200); arrList.add(300); arrList.add(400); arrList.add(500); arrList.add(600); arrList.add(700); arrList.add(800); arrList.add(900); arrList.add(1000);Now, create a ListIterator −ListIteratoriterator = arrList.listIterator();Get the previous and next index now −iterator.previousIndex(); iterator.nextIndex();Exampleimport java.util.ArrayList; import java.util.ListIterator; public class Demo { public static void main(String[] args) { ArrayListarrList = new ArrayList(); arrList.add(100); ...
Read MoreHow to remove all elements from a Collection in another Collection
Let’s say the following is our Collection i.e. ArrayList −Listlist = new ArrayList(); list.add(100); list.add(200); list.add(200); list.add(200); list.add(300); list.add(400); list.add(400); list.add(500);Now, create another Collection −List list2 = new ArrayList(); list2.add(100); list2.add(200); list2.add(300); list2.add(400);To remove all elements from a Collection in another Collection, try the following with list and list2 as our two Collections −list.removeAll(list2);Exampleimport java.util.ArrayList; import java.util.List; public class Demo { public static void main(String args[]) throws Exception { Listlist = new ArrayList(); list.add(100); list.add(200); list.add(200); list.add(200); list.add(300); ...
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