Few Python examples to show you how to generate random integers between 0 (inclusive) and 9 (inclusive) 0 1 2 3 4 5 6 7 8 9 1. randrange 1.1 Generates random integers between 0 – 9 #!/usr/bin/python import random for i in range(10): print(random.randrange(10)) # 0-9 Output 7 4 1 1 5 1 4 […]
In Java 13, the JEP 354: Switch Expressions extends the previous Java 12 Switch Expressions by adding a new yield keyword to return a value from the switch expression. P.S Switch expressions are a preview feature and are disabled by default. Note This is a standard feature in Java 14. 1. No more value breaks! […]
Java 13 reached General Availability on 17 September 2019, download Java 13 here or this openJDK archived. Java 13 features. 1. JEP 350 Dynamic CDS Archives 2. JEP 351 ZGC: Uncommit Unused Memory 3. JEP-353 Reimplement the Legacy Socket API 4. JEP-354 Switch Expressions (Preview) 5. JEP-355 Text Blocks (Preview) Java 13 developer features. Switch […]
This article shows you how to use JUnit 5 Assumptions to perform a conditional test execution. Technologies used: Maven 3.6 Java 8 JUnit 5.5.2 1. Assumptions 1.1 If the assumeTrue() condition is true, then run the test, else aborting the test. 1.2 The assumingThat() is much more flexible, it allows part of the code to […]
This article shows you how to update the IntelliJ IDEA to use the new JDK 13. 1. On the menu, clicks File -> Project Structure 2. Platform Settings -> SDKs, add and point to the JDK 13 installed folder. 3. Project Settings -> Project, change both Project SDK and Project language level to JDK 13. […]
In Python, we can use index -1 to get the last element of a list. #!/usr/bin/python nums = [1, 2, 3, 4, 5] print(nums[-1]) print(nums[-2]) print(nums[-3]) print(nums[-4]) print(nums[-5]) print(nums[0]) print(nums[1]) print(nums[2]) print(nums[3]) print(nums[4]) Output 5 4 3 2 1 1 2 3 4 5 Yet another example. #!/usr/bin/python # getting list of nums from the […]
This article shows you how to add JUnit 5 in a Gradle project. Technologies used: Gradle 5.4.1 Java 8 JUnit 5.5.2 1. Gradle + JUnit 5 1. Add the JUni 5 jupiter engine, and define the useJUnitPlatform() like the following: gradle.build plugins { id ‘java’ id ‘eclipse’ // optional, for Eclipse project id ‘idea’ // […]
This article shows you how to add JUnit 5 in a Maven project, nothing special, just add the JUnit 5 junit-jupiter-engine library and make sure the maven-surefire-plugin is at least version 2.22.0 Technologies used: Maven 3.6 Java 8 JUnit 5.5.2 1. Maven + JUnit 5 1. Add the JUni 5 jupiter engine. pom.xml <dependency> <groupId>org.junit.jupiter</groupId> […]
In this tutorial, we are going to learn how to add / concatenate two lists in Python. What Is Concatenation? Concatenation of lists is an operation where the elements of one list are added at the end of another list. For example, if we have a list with elements [1, 2, 3] and another list […]
Java 12, JEP 325: Switch Expressions enhanced the traditional switch statement to support the following new features: Multiple case labels Switch expression returning value via break (replaced with yield in Java 13 switch expressions) Switch expression returning value via label rules (arrow) P.S Switch expressions are a preview feature and are disabled by default. A […]
In Python trim method is called strip, it removes the leading and trailing spaces of a String. str.strip() #trim str.lstrip() #ltrim str.rstrip() #rtrim #!/usr/bin/python str = " abc " print(str) print(str.strip()) print(str.lstrip()) print(str.rstrip()) Output {space} abc {space} abc abc {space} {space} abc References Python docs str.strip()
In Java, index starts at 0, we can get the last index of a list via this formula: list.size() – 1 JavaExample1.java package com.mkyong.test; import java.util.Arrays; import java.util.List; public class JavaExample1 { public static void main(String[] args) { List<Integer> list = Arrays.asList(1, 2, 3, 4, 5); System.out.println(list.get(list.size() – 1)); System.out.println(list.get(list.size() – 2)); System.out.println(list.get(list.size() – 3)); […]
In Java, we can get the keys and values via map.entrySet() Map<String, String> map = new HashMap<>(); // Get keys and values for (Map.Entry<String, String> entry : map.entrySet()) { String k = entry.getKey(); String v = entry.getValue(); System.out.println("Key: " + k + ", Value: " + v); } // Java 8 map.forEach((k, v) -> { […]
Spring JdbcTemplate example to get a large ResultSet and process it. P.S Tested with Java 8 and Spring JDBC 5.1.4.RELEASE 1. Get large ResultSet 1.1 Below is a classic findAll to get all data from a table. BookRepository.java public List<Book> findAll() { return jdbcTemplate.query( "select * from books", (rs, rowNum) -> new Book( rs.getLong("id"), rs.getString("name"), […]
Below example, the jdbcTemplate.queryForList returns an object of Integer and we try to convert it into a Long directly: public List<Customer> findAll() { String sql = "SELECT * FROM CUSTOMER"; List<Customer> customers = new ArrayList<>(); List<Map<String, Object>> rows = jdbcTemplate.queryForList(sql); for (Map row : rows) { Customer obj = new Customer(); obj.setID(((Long) row.get("ID"))); // the […]
In Java, we can combine RandomAccessFile and FileChannel to lock a file before writing. LockFileAndWrite.java package com.mkyong; import java.io.File; import java.io.IOException; import java.io.RandomAccessFile; import java.nio.channels.FileLock; import java.util.concurrent.TimeUnit; public class LockFileAndWrite { public static void main(String[] args) { writeFileWithLock(new File("D:\\server.log"), "mkyong"); } public static void writeFileWithLock(File file, String content) { // auto close and release the […]
In Java, we can use the Apache Commons IO ReversedLinesFileReader to read the last few lines of a File. pom.xml <dependency> <groupId>commons-io</groupId> <artifactId>commons-io</artifactId> <version>2.6</version> </dependency> 1. Test Data A server log file sample d:\\server.log a b c d 1 2 3 4 5 2. Read Last Line 2.1 Read the last 3 lines of a […]
In this tutorial, we will show you how to use Spring Boot JDBC SimpleJdbcCall to call a stored procedure and stored function from a Oracle database. Technologies used : Spring Boot 2.1.2.RELEASE Spring JDBC 5.1.4.RELEASE Oracle database 19c HikariCP 3.2.0 Maven 3 Java 8 Unlike JdbcTemplate, Spring Boot didn’t create any SimpleJdbcCall automatically, we have […]
In this tutorial, we will show you how to use Spring Boot JDBC JdbcTemplate and NamedParameterJdbcTemplate. Technologies used : Spring Boot 2.1.2.RELEASE Spring JDBC 5.1.4.RELEASE HikariCP 3.2.0 H2 in-memory database 1.4.197 Maven 3 Java 8 In Spring Boot JDBC, the database related beans like DataSource, JdbcTemplate and NamedParameterJdbcTemplate will be configured and created during the […]
Java 8 stream and regular expression examples. Note Learn the basic regular expression at Wikipedia 1. String.matches(regex) 1.1 This example, check if the string is a number. JavaRegEx1.java package com.mkyong.regex; import java.util.Arrays; import java.util.List; public class JavaRegEx1 { public static void main(String[] args) { List<String> numbers = Arrays.asList("1", "20", "A1", "333", "A2A211"); for (String number […]
As title, we can use flatMap to convert it. Java9Example1.java package com.mkyong.test; import java.util.Arrays; import java.util.List; import java.util.Scanner; import java.util.stream.Collectors; public class Java9Example1 { public static void main(String[] args) { List<String> numbers = Arrays.asList("1", "2", "A", "B", "C1D2E3"); List<List<String>> collect = numbers.stream() .map(x -> new Scanner(x).findAll("\\D+") .map(m -> m.group()) .collect(Collectors.toList()) ) .collect(Collectors.toList()); collect.forEach(x -> System.out.println(x)); […]
In this tutorial, we are going to learn how to delete a file or directory in Python. The process of removing a file or folder in Python is straightforward using the os module. os.remove – Deletes a file. os.rmdir – Deletes a folder. shutil.rmtree – Deletes a directory and all its contents. 1. Deletes a […]
Call the .values() method of the enum class to return an array, and loop it with the for loop: for (EnumClass obj : EnumClass.values()) { System.out.println(obj); } For Java 8, convert an enum into a stream and loop it: Stream.of(EnumClass.values()).forEach(System.out::println); 1. For Loop Enum 1.1 An enum to contain a list of the popular JVM […]
Making a JDBC connection to the MySQL server with the latest mysql-connector-java:8.0.16 and hits the following SQLException: Tested with MySQL 5.7 Java 8 JDBC driver, mysql-connector-java 8.0.16 try (Connection conn = DriverManager.getConnection( "jdbc:mysql://127.0.0.1:3306/test", "root", "password")) { //… } catch (Exception e) { e.printStackTrace(); } Output java.sql.SQLException: The server time zone value ‘Malay Peninsula Standard Time’ […]
In Java, we can use Long.valueOf() to convert an Integer to a Long TestInteger.java package com.mkyong.example; public class TestInteger { public static void main(String[] args) { Integer num = 1; System.out.println(num); // 1 Long numInLong = Long.valueOf(num); System.out.println(numInLong); // 1 } } References Long.valueOf JavaDocs)
Few Java 8 examples to execute streams in parallel. 1. BaseStream.parallel() A simple parallel example to print 1 to 10. ParallelExample1.java package com.mkyong.java8; import java.util.stream.IntStream; public class ParallelExample1 { public static void main(String[] args) { System.out.println("Normal…"); IntStream range = IntStream.rangeClosed(1, 10); range.forEach(System.out::println); System.out.println("Parallel…"); IntStream range2 = IntStream.rangeClosed(1, 10); range2.parallel().forEach(System.out::println); } } Output Normal… 1 2 […]
The following Java examples will print a list of all the prime numbers up to 1,000: 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97 101 103 107 109 113 127 131 137 139 149 151 157 163 167 […]
Ordinal binding or index binding: String name = stat.getString(2); BigDecimal salary = stat.getBigDecimal(3); Timestamp createdDate = stat.getTimestamp(4); Named binding: String name = stat.getString("NAME"); BigDecimal salary = stat.getBigDecimal("SALARY"); Timestamp createdDate = stat.getTimestamp("CREATED_DATE"); If we mixed both like this: String name = stat.getString(2); BigDecimal salary = stat.getBigDecimal("SALARY"); Timestamp createdDate = stat.getTimestamp(4); Error: java.sql.SQLException: operation not allowed: Ordinal […]
Java example to convert java.time.ZonedDateTime to java.sql.Timestamp and vice verse. 1. ZonedDateTime -> Timestamp TimeExample1.java package com.mkyong.jdbc; import java.sql.Timestamp; import java.time.ZonedDateTime; public class TimeExample1 { public static void main(String[] args) { ZonedDateTime now = ZonedDateTime.now(); // 1. ZonedDateTime to TimeStamp Timestamp timestamp = Timestamp.valueOf(now.toLocalDateTime()); // 2. ZonedDateTime to TimeStamp , no different Timestamp timestamp2 = […]
Python example to print the key value of a dictionary. stocks = { ‘IBM’: 146.48, ‘MSFT’: 44.11, ‘CSCO’: 25.54 } print(stocks) for k, v in stocks.items(): print(k, v) for k in stocks: print(k, stocks[k]) Output {‘IBM’: 146.48, ‘MSFT’: 44.11, ‘CSCO’: 25.54} IBM 146.48 MSFT 44.11 CSCO 25.54 IBM 146.48 MSFT 44.11 CSCO 25.54 References Python […]
Many examples are using the .count() as the terminal operation for .peek(), for example: Java 8 List<String> l = Arrays.asList("A", "B", "C", "D"); long count = l.stream().peek(System.out::println).count(); System.out.println(count); // 4 Output – It’s working fine. A B C D 4 However, for Java 9 and above, the peek() may print nothing: Java 9 and above […]
In Java, we can use Timestamp.valueOf(LocalDateTime) to convert a LocalDateTime into a Timestamp. 1. LocalDateTime Timestamp Java example to convert java.time.LocalDateTime to java.sql.Timestamp and vice verse. TimeExample.java package com.mkyong; import java.sql.Timestamp; import java.time.LocalDateTime; public class TimeExample { public static void main(String[] args) { // LocalDateTime to Timestamp LocalDateTime now = LocalDateTime.now(); Timestamp timestamp = Timestamp.valueOf(now); […]
Some Java Conferences and Events 2019. 1. JAX London (October 7–10, 2019) JAX London is a four-day conference for cutting edge software engineers and enterprise-level professionals. JAX brings together the world’s leading innovators in the fields of JAVA, microservices, continuous delivery and DevOps. Date: October 7–10, 2019 Location: Business Design Centre, London Discount(15%): mky_jxl19#15 Twitter: […]
This is caused by the requested SID doesn’t exist in {ORACLE_HOME}/network/admin/tnsnames.ora P.S Tested with Oracle database 19c with ojdbc8.jar 1. JDBC try (Connection conn = DriverManager.getConnection( "jdbc:oracle:thin:@localhost:1521:xe", "system", "password")) { //… } catch (SQLException e) { e.printStackTrace(); } catch (Exception e) { e.printStackTrace(); } Output: SQL State: 66000 Listener refused the connection with the following […]
To uninstall Oracle database on Windows, we have to delete the all the related Ora* registry keys, files and folders manually. P.S Tested with Oracle database 19c on Windows 10 Note I can’t find any uninstaller to uninstall the Oracle database automatically? 1. Stop Oracle* services Press Windows key, type services, stop all Oracle related […]
A JDBC CallableStatement example to show you how to call a stored function from PostgreSQL database. P.S Tested with PostgreSQL 11 and Java 8 pom.xml <dependency> <groupId>org.postgresql</groupId> <artifactId>postgresql</artifactId> <version>42.2.5</version> </dependency> 1. Call Function 1.1 Create a stored function and calling it via JDBC. FunctionReturnString.java package com.mkyong.jdbc.callablestatement; import java.sql.*; public class FunctionReturnString { public static void […]
Since Java 1.6, JDBC 4.0 API, it provides a new feature to discover java.sql.Driver automatically, it means the Class.forName is no longer required. Just put any JDBC 4.x driver in the project classpath, and Java is able to detect it. For example, JDBC driver for PostgreSQL: pom.xml <dependency> <groupId>org.postgresql</groupId> <artifactId>postgresql</artifactId> <version>42.2.5</version> </dependency> And it works: […]
A JDBC example to connect to a PostgreSQL, and print out all the tables from the default database postgres pom.xml <dependencies> <dependency> <groupId>org.postgresql</groupId> <artifactId>postgresql</artifactId> <version>42.2.5</version> </dependency> </dependencies> P.S Tested with Java 8 and postgresql jdbc driver 42.2.5 PrintAllTables.java package com.mkyong.jdbc; import java.sql.*; public class PrintAllTables { public static void main(String[] argv) { System.out.println("PostgreSQL JDBC Connection […]
If Java 8, DateTimeFormatter, else SimpleDateFormat to change the date format in a String. 1. DateTimeFormatter (Java 8) Convert the String to LocalDateTime and change the date format with DateTimeFormatter DateFormatExample1.java package com.mkyong; import java.time.LocalDateTime; import java.time.format.DateTimeFormatter; public class DateFormatExample1 { // date format 1 private static final DateTimeFormatter dateFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss.S"); // date […]
Different operating system has a different new line or line separator string: UNIX, Linux or Mac OSX = \n Windows = \r\n NewLineExample.java package com.mkyong; public class NewLineExample { public static void main(String[] args) { String original = "Hello World Java"; System.out.println(original); // add new line String originalNewLine = "Hello\nWorld\nJava"; System.out.println(originalNewLine); } } Output Hello […]
