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Java Articles
Page 43 of 450
Initializer for final static field in Java
The final static field variable is a constant variable. There is only one copy of this variable available. It is mandatory to initialize the final static field variable explicitly as the default value for it is not provided by the JVM. Also, this variable cannot be reinitialized.A program that initializes the final static field variable using a static initialization block is given as follows:Examplepublic class Demo { final static int num; static { System.out.println("Running static initialization block."); num = 6; } public static void main(String[] args) { ...
Read MoreFinding all words that start with an 'a' in Java
All the words that start with a can be found in a string by using regular expressions in Java. The regular expressions are character sequences that can be used to match other strings using a specific pattern syntax. The regular expressions are available in the java.util.regex package which has many classes but the most important are Pattern class and Matcher class.A program that finds all words that start with an 'a' is using regular expressions is given as follows:Exampleimport java.util.regex.Matcher; import java.util.regex.Pattern; public class Demo { public static void main(String args[]) throws Exception { String str ...
Read MoreA Reluctant qualifier in Java Regular Expressions
The reluctant qualifier starts with the shortest string size as possible. If a match is found by the engine, the process continues to find more matches otherwise the engine adds a character to the searched string section and tries again. This continues until a match is obtained or the string is used up.The regex "B+?" is used to find the match in the string "SkyIsBlue".A program that demonstrates this is given as follows:Exampleimport java.util.regex.Matcher; import java.util.regex.Pattern; public class Demo { public static void main(String args[]) { String regex = "B+?"; String str = ...
Read MoreUse a character class in Java Regular Expressions
A character class is set of characters that are enclosed inside square brackets. The characters in a character class specify the characters that can match with a character in an input string for success. An example of a character class is [a-z] which denotes the alphabets a to z.A program that demonstrates a character class in Java Regular Expressions is given as follows:Exampleimport java.util.regex.Matcher; import java.util.regex.Pattern; public class Demo { public static void main(String args[]) { Pattern p = Pattern.compile("[a-z]+"); Matcher m = p.matcher("the sky is blue"); System.out.println("The input string ...
Read MoreName validation using Java Regular Expressions
The name can be validated using the java.util.regex.Pattern.matches() method. This method matches the regular expression for the name and the given input name and returns true if they match and false otherwise.A program that demonstrates this is given as follows:Examplepublic class Demo { public static void main(String args[]) { String name = "John Harry Smith"; String regexName = "\p{Upper}(\p{Lower}+\s?)"; String patternName = "(" + regexName + "){2, 3}"; System.out.println("The name is: " + name); System.out.println("Is the above name valid? " + name.matches(patternName)); } ...
Read MoreCreate a directory in Java
A directory can be created with the required abstract path name using the method java.io.File.mkdir(). This method requires no parameters and it returns true on the success of the directory creation or false otherwise.A program that demonstrates this is given as follows −Exampleimport java.io.File; public class Demo { public static void main(String[] args) { try { File file = new File("c:\demo1"); file.createNewFile(); boolean flag = file.mkdir(); System.out.print("Directory created? " + flag); } catch(Exception e) { ...
Read MoreDisplay File class constants in Java
The java.io.File class has display constants File.separatorChar and File.pathSeparatorChar mainly. The File.separatorChar is ‘/’ and the File.pathSeparatorChar is ‘:’ for Unix.A program that demonstrates this is given as follows −Exampleimport java.io.File; public class Demo { public static void main(String[] args) { try { System.out.println("File.pathSeparatorChar = " + File.pathSeparatorChar); System.out.println("File.separatorChar = " + File.separatorChar); } catch(Exception e) { e.printStackTrace(); } } }The output of the above program is as follows −OutputFile.pathSeparatorChar = : File.separatorChar = /Now let us ...
Read MoreList the file system roots in Java
The method java.io.File.listRoots() is used to list the file system roots in Java. This method requires no parameters. It returns the available file system roots in the form of an array of file objects and if the file system roots cannot be determined, it returns null.A program that demonstrates this is given as follows −Exampleimport java.io.File; public class Demo { public static void main(String[] args) { File[] roots = File.listRoots(); try { for(File r : roots) { System.out.println(r); } ...
Read MoreGet file extension name in Java
The file extension is the suffix that is attached to the computer file and it denotes the format of the file. A program that demonstrates getting the file extension name is given as follows −Exampleimport java.io.File; public class Demo { private static String fileExtension(File file) { String name = file.getName(); if(name.lastIndexOf(".") != -1 && name.lastIndexOf(".") != 0) return name.substring(name.lastIndexOf(".") + 1); else return ""; } public static void main(String[] args) { File file = new File("demo1.txt"); ...
Read MoreFile Path with double slash in Java
The double slash in the file path is required as to create the ’\’ character , another ‘\’ needs to be added to escape it. A program that demonstrates this is given as follows −Exampleimport java.io.File; public class Demo { public static void main(String[] args) { File file = new File("C:\jdk11.0.2\demo1.txt"); System.out.println(file); } }The output of the above program is as follows −OutputC:\jdk11.0.2\demo1.txtNow let us understand the above program.The file path of the file is provided with double slash and then it is printed. A code snippet that demonstrates this is given ...
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