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Object Oriented Programming Articles
Page 451 of 589
Difference between HashMap and ConcurrentHashMap in Java
Following are the notable differences between HashMap and ConcurrentHashMap classes in Java. HashMapConcurrentHashMapSynchronizedHashMap is not synchronized.ConcurrentHashMap is synchronized.Thread SafeHashMap is not thread safe.ConcurrentHashMap is thread safe.Iterator typeHashMap iterator is fail-fast and ArrayList throws ConcurrentModificationException if concurrent modification happens during iteration.ConcurrentHashMap is fail-safe and it will never throw ConcurrentModificationException during iteration.Null valuesHashMap allows key and value to be null.ConcurrentHashMap does not allow null key/value. It will throw NullPointerException.PerformanceHashMap is faster.ConcurrentHashMap is slower than HashMap.Since Java Version1.21.5Exampleimport java.util.ArrayList; import java.util.Iterator; import java.util.List; import java.util.concurrent.CopyOnWriteArrayList; public class Tester { public static void main(String[] args) { ...
Read MoreHow to extract a group from a Java String that contains a Regex pattern
How to extract a group from a Java String that contains a Regex patternimport java.util.regex.Matcher; import java.util.regex.Pattern; public class RegexTest { public static void main(String[] args) { Pattern pattern = Pattern.compile("fun"); Matcher matcher = pattern.matcher("Java is fun"); // using Matcher find(), group(), start() and end() methods while (matcher.find()) { System.out.println("Found the text "" + matcher.group() + "" starting at " + matcher.start() + " index and ending at index ...
Read MoreHow to capture multiple matches in the same line in Java regex
Exampleimport java.util.regex.*; class PatternMatcher { public static void main(String args[]) { int count = 0; // String to be scanned to find the pattern. String content = "aaa bb aaa"; String string = "aaa"; // Create a Pattern object Pattern p = Pattern.compile(string); // get a matcher object Matcher m = p.matcher(content); while(m.find()) { count++; System.out.println("Match no:"+count); ...
Read MoreJava Regular Expression that doesn't contain a certain String.
Exampleimport java.util.regex.*; class PatternMatch{ public static void main(String args[]) { String content = "I am a student"; String string = ".*boy.*"; boolean isMatch = Pattern.matches(string, content); System.out.println("The line contains 'boy'?"+ isMatch); } }Outputthe line contains 'boy'?falsematches()It is used to check if the whole text matches a pattern. Its output is boolean. It returns true if match is found otherwise false.This is one of simplest and easiest way of searching a String in a text using Regex .There is a another method compile() , if you want ...
Read MoreDatabase operations in Java
This article provides an example of how to create a simple JDBC application. This will show you how to open a database connection, execute a SQL query, and display the results.Creating JDBC ApplicationThere are following six steps involved in building a JDBC application −Import the packages: Requires that you include the packages containing the JDBC classes needed for database programming. Most often, using import java.sql.* will suffice.Register the JDBC driver: Requires that you initialize a driver so you can open a communication channel with the database.Open a connection: Requires using the DriverManager.getConnection() method to create a Connection object, which represents ...
Read MoreCounting number of paragraphs in text file using java
We can read paragraphs in a file by reading it in a string and then spilting based on "\r" pattern. See the example below −ExampleConsider the following text file in the classpath.test.txtThis is Line 1 This is Line 2 This is Line 3 This is Line 4 This is Line 5 This is Line 6 This is Line 7 This is Line 8 This is Line 9 This is Line 10Tester.javaimport java.io.File; import java.io.FileInputStream; import java.io.IOException; public class Tester { public static void main(String args[]) throws IOException { FileUtil fileUtil = ...
Read MoreCounting number of characters in text file using java
We can read characters in a file using BufferedReader class of Java. See the example below −ExampleConsider the following text file in the classpath.test.txtThis is Line 1 This is Line 2 This is Line 3 This is Line 4 This is Line 5 This is Line 6 This is Line 7 This is Line 8 This is Line 9 This is Line 10Tester.javaimport java.io.BufferedReader; import java.io.File; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.IOException; import java.io.InputStreamReader; public class Tester { private static final String FILE_PATH = "data.txt"; public static void main(String args[]) throws IOException { ...
Read MoreCreate translucent windows in Java Swing
With JDK 7, we can create a translucent window using swing very easily. With following code, a JFrame can be made translucent.// Set the window to 55% opaque (45% translucent). frame.setOpacity(0.55f);ExampleSee the example below of a window with 55% translucency.import java.awt.GridBagLayout; import javax.swing.JButton; import javax.swing.JFrame; import javax.swing.SwingUtilities; public class Tester { public static void main(String[] args) { JFrame.setDefaultLookAndFeelDecorated(true); // Create the GUI on the event-dispatching thread SwingUtilities.invokeLater(new Runnable() { @Override public void ...
Read MoreConversion of Set To Stream in Java
Being a type of Collection, we can convert a set to Stream using its stream() method. Example import java.util.HashSet; import java.util.Set; import java.util.stream.Stream; public class Tester { public static void main(String args[]) { Set<String> set = new HashSet<String>(); set.add("a"); set.add("b"); set.add("c"); set.add("d"); set.add("e"); set.add("f"); Stream<String> stream = set.stream(); stream.forEach(data->System.out.print(data+" ")); } } Output a b c d e f
Read MoreCharacter Stream vs Byte Stream in Java
Byte StreamsJava byte streams are used to perform input and output of 8-bit bytes. Though there are many classes related to byte streams but the most frequently used classes are, FileInputStream and FileOutputStream. Following is an example which makes use of these two classes to copy an input file into an output file −Exampleimport java.io.*; public class CopyFile { public static void main(String args[]) throws IOException { FileInputStream in = null; FileOutputStream out = null; try { in = new ...
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