In Java, we can use Integer.toBinaryString(int) to convert an Integer to a binary string representative. Integer.java public final class Integer extends Number implements Comparable<Integer>, Constable, ConstantDesc { public static String toBinaryString(int i) { return toUnsignedString0(i, 1); } //… } This article will show you two methods to convert an Integer to a binary string representative. […]
In this article, we will show you a few ways to reverse a String in Java. StringBuilder(str).reverse() char[] looping and value swapping. byte looping and value swapping. Apache commons-lang3 For development, always picks the standard StringBuilder(str).reverse() API. For educational purposes, we can study the char[] and byte methods, it involved value swapping and bitwise shifting […]
In Java, we can use Integer.toBinaryString(int) to convert a byte to a binary string representative. Review the Integer.toBinaryString(int) method signature, it takes an integer as argument and returns a String. Integer.java public final class Integer extends Number implements Comparable<Integer>, Constable, ConstantDesc { public static String toBinaryString(int i) { return toUnsignedString0(i, 1); } //… } If […]
Review the following Java example to convert a negative integer in binary string back to an integer type. String binary = Integer.toBinaryString(-1); // convert -1 to binary // 11111111 11111111 11111111 11111111 (two’s complement) int number = Integer.parseInt(binary, 2); // convert negative binary back to integer System.out.println(number); // output ?? The result is NumberFormatException! Exception […]
In Java, Sign extension will kick in if we are doing the following stuff: Widening primitive conversion – Cast from one type to another, which involves increasing the bits of the original type, for example, cast byte (8 bits) to int (32 bits). Bitwise right shift by n bit >> n. The sign extension is […]
In Python, the fastest and easiest way to reverse a string is the extended slice, [::-1]. print("hello world"[::-1]) # dlrow olleh This article will show you a few ways to reverse a string in Python. [::-1] reverse order slice. (Good) [::-1] slice implement as function. (Good) Reversed and Join (Reverse String and Words) (Ok) Python […]
In programming, bitwise shift operators, >> means arithmetic right shift, >>> means logical right shift, the differences: >>, it preserves the sign (positive or negative numbers) after right shift by n bit, sign extension. >>>, it ignores the sign after right shift by n bit, zero extension. To work with bitwise shift operators >> and […]
This article shows you how to make IntelliJ IDEA support and run Python. P.S Make sure Python SDK is installed, later we need to link this Python SDK to IntelliJ IDEA. 1. Plugins In IntelliJ IDEA. File -> Settings -> Plugins. 2. Python Community Edition Clicks Marketplace, search python, install the Python Community Edition by […]
The Advanced Encryption Standard (AES, Rijndael) is a block cipher encryption and decryption algorithm, the most used encryption algorithm in the worldwide. The AES processes block of 128 bits using a secret key of 128, 192, or 256 bits. This article shows you a few of Java AES encryption and decryption examples: AES String encryption […]
JUnit 5 = JUnit Platform + JUnit Jupiter + JUnit Vintage P.S JUnit 5 requires Java 8 (or higher) at runtime 1. JUnit 5 + Maven See this full JUnit 5 + Maven examples. pom.xml <dependency> <groupId>org.junit.jupiter</groupId> <artifactId>junit-jupiter-engine</artifactId> <version>5.5.2</version> <scope>test</scope> </dependency> <build> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-surefire-plugin</artifactId> <version>3.0.0-M3</version> </plugin> </plugins> </build> P.S The maven-surefire-plugin must be […]
On Docker, –rm option means automatically remove the container when it exits. $ docker run –rm <container_id> Done 🙂 Please read on to understand more about –rm. 1. Remove a container On Docker, the container is an instance of an image, and we can create multiple containers from an image. If the container is exited […]
This article is introducing the Java 14 new feature – record or data class, defined in JEP 359. P.S This record data class is a preview feature Why record? Java is too verbose, if we want to declare a class, we need to create a lot of tedious and repetitive methods like constructors, accessors, equals(), […]
In Docker, we can use docker ps to show all running containers, docker ps -a to show all running and stopped containers. Here are some of the commonly used examples: Terminal # common $ docker ps // show only running containers $ docker ps -a // show all containers (running and stopped or exited) # […]
This article will show you a few ways to declare and use a multi-line string in Java. String + String + String StringBuilder String.format StringWriter String.join (Java 8) Files.lines (Java 8) (""") Java 13 and Java 14 text blocks (preview feature) Review an HTML and a JSON string, and we will use the above methods […]
Java 12 reached General Availability on 19 March 2019, download Java 12 here or this openJDK archived. Java 12 features. 1. JEP 189: Shenandoah: A Low-Pause-Time Garbage Collector (Experimental) 2. JEP 230: Microbenchmark Suite 3. JEP 325: Switch Expressions (Preview) 4. JEP 334: JVM Constants API 5. JEP 340: One AArch64 Port, Not Two 6. […]
To exit JShell, type /exit. I stuck in JShell for minutes, commands like exit, ctrl + c, end, q!, q, quit all failed, the correct syntax to quit or exit the JShell is /exit. Terminal C:\Users\mkyong>jshell | Welcome to JShell — Version 11.0.1 | For an introduction type: /help intro jshell> exit | Error: | […]
Java 11 reached General Availability on 25 September 2018, this is a Long Term Support (LTS) version, download Java 11 here or this openJDK archived. Java 11 features. 1. JEP 181: Nest-Based Access Control 2. JEP 309: Dynamic Class-File Constants 3. JEP 315: Improve Aarch64 Intrinsics 4. JEP 318: Epsilon: A No-Op Garbage Collector (Experimental) […]
This Java 11 JEP 332 adds support for TLS 1.3 protocol. SSLSocket + TLS 1.3 An SSLSocket client with TLS1.3 protocol and TLS_AES_128_GCM_SHA256 stream cipher, to send a request to https://google.com and print the response. JavaTLS13.java package com.mkyong.java11.jep332; import javax.net.ssl.SSLSocket; import javax.net.ssl.SSLSocketFactory; import java.io.*; // Java 11 public class JavaTLS13 { private static final String[] […]
In Java 11, JEP 330 adds support to run single-file source code directly. Terminal # Before Java 11 $ javac Hello.java $ java Hello # Now Java 11 $ java Hello.java This indirectly supports the Java single-file program to run as a script using Unix Shebang. For example, run below .sh file will print Hello […]
In IntelliJ IDEA, we need to enable this auto-generate serialVersionUID option manually. P.S Tested with IntelliJ IDEA 2019.3.4, it should work the same in other versions. Intellij IDEA Settings File -> Settings -> Editor -> Inspections -> Java -> Serialization issues: Find serialization class without serialVersionUID and check it. Back to the editor, clicks on […]
In Java, we can use SecureRandom.nextBytes(byte[] bytes) to generate a user-specified number of random bytes. This SecureRandom is a cryptographically secure random number generator (RNG). 1. Random 12 bytes (96 bits) 1.1 Generates a random 12 bytes (96 bits) nonce. HelloCryptoApp.java package com.mkyong.crypto; import java.security.SecureRandom; public class HelloCryptoApp { public static void main(String[] args) { […]
This article shows you how to encrypt and decrypt a message with the ChaCha20-Poly1305 algorithm, defined in RFC 7539. P.S The ChaCha20-Poly1305 encryption algorithm is available at Java 11. 1. FAQs Some commonly asked questions: 1.1 What is ChaCha20-Poly1305? ChaCha20-Poly1305 means the ChaCha20 (encryption and decryption algorithm) running in AEAD mode with the Poly1305 authenticator. […]
docker run a container, but it displayed nothing, no output, no error? docker ps shows no running container? Terminal $ docker run -d -p 80:8080 -p 443:8443 -t markdownhtml:1.1 8eba06d44bf236109cf65b7b93842e9c898370cac1740aa2bab557a0fc8e52b9 $ docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES Solution Most of the time, the container hit an error and exited automatically. We […]
In this article, we will show you how to encrypt and decrypt a message with the ChaCha20 stream cipher, defined in RFC 7539. P.S ChaCha20 stream cipher is available at Java 11, refer to JEP 329. Note You may interest at this ChaCha20-Poly1305 encryption examples 1. How it works? 1.1 The inputs to ChaCha20 encryption […]
In this example, we will show you how to join and split byte arrays with ByteBuffer and System.arraycopy. ByteBuffer public static byte[] joinByteArray(byte[] byte1, byte[] byte2) { return ByteBuffer.allocate(byte1.length + byte2.length) .put(byte1) .put(byte2) .array(); } public static void splitByteArray(byte[] input) { ByteBuffer bb = ByteBuffer.wrap(input); byte[] cipher = new byte[8]; byte[] nonce = new byte[4]; […]
In Java, we can use ByteBuffer to convert int to byte[] and vice versa. int to byte[] int num = 1; // int need 4 bytes, default ByteOrder.BIG_ENDIAN byte[] result = ByteBuffer.allocate(4).putInt(number).array(); byte[] to int byte[] byteArray = new byte[] {00, 00, 00, 01}; int num = ByteBuffer.wrap(bytes).getInt(); 1. int to byte[] This Java example […]
In this article, we will show you how to use docker cp to copy files or folders from a docker container to the host (local file system) or the reversed. For example, here is a running container, id is d362659da5fc, later we will copy files from and to this container. Terminal $ docker ps CONTAINER […]
In Java, Serialization means converting Java objects into a byte stream; Deserialization means converting the serialized object’s byte stream back to the original Java object. Table of contents. 1. Hello World Java Serialization 2. java.io.NotSerializableException 3. What is serialVersionUID? 4. What is transient? 5. Serialize Object to File 6. Why need Serialization in Java? 7. […]
Java Flight Recorder (JFR) is a Java profiling tool that used to monitor and diagnose a running Java application, it collects data about the running environment, JVM and Java application and dumps the recorded data into a .jfr file, and we can use Java Mission Control (JMC) to analyze and visualize the .jfr file. Tested […]
In Python, we can use bin() or format() to convert an integer into a binary string representation. print(bin(1)) # 0b1 print(bin(-1)) # -0b1 print(bin(10)) # 0b1010 print(bin(-10)) # -0b1010 print("{0:b}".format(10)) # 1010 print("{0:#b}".format(10)) # 0b1010 , with 0b prefix print("{0:b}".format(10).zfill(8)) # 00001010 , pad zero, show 8 bits print(format(10, "b")) # 1010 print(format(10, "#b")) # […]
If bash shell is not working, try sh. Terminal $ docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 3d1588519433 markdownhtml:0.1 "java -jar app.jar" About an hour ago Up About an hour 0.0.0.0:80->8080/tcp gracious_haibt $ docker exec -it 3d1588519433 bash OCI runtime exec failed: exec failed: container_linux.go:349: starting container process caused "exec: \"bash\": executable […]
In Java, transient fields are excluded in the serialization process. In short, when we save an object into a file (serialization), all transient fields are ignored. 1. POJO + transient Review the following Person class; the salary field is transient. public class Person implements Serializable { private static final long serialVersionUID = 1L; private String […]
The jcmd is available at the JDK/bin, not JRE. Make sure the installed Java is JDK, not JRE. Let review the following example, try to use jcmd to enable Java Flight Recorder inside a docker container. 1. DockerFile A simple Dokcerfile. Dockerfile FROM adoptopenjdk/openjdk11:alpine-jre ARG JAR_FILE=target/markdown.jar WORKDIR /opt/app COPY ${JAR_FILE} app.jar ENTRYPOINT ["java","-jar","app.jar"] 2. Docker […]
We installed Nginx, MariaDB, PHP, and WordPress on Mac OS. The homepage is displayed fine, but all other pages are returning 404 errors? Tested with Nginx 1.17.9 WordPress 5.4 PHP 7.4 Review the current Nginx + WordPress integration. nginx.conf server { listen 8080; server_name localhost; root /usr/local/var/www/wordpress; location / { index index.html index.htm index.php; } […]
This article shows you how to use docker exec -it <container ID or Name> <sh or bash> to access or get into the container’s shell. Terminal # docker exec -it <contaier ID or name> <command> $ docker exec -it a5df11a07a0e bash /opt/app # $ docker exec -it stoic_bhaskara sh /opt/app # The docker exec -it […]
The MD5, defined in RFC 1321, is a hash algorithm to turn inputs into a fixed 128-bit (16 bytes) length of the hash value. Note MD5 is not collision-resistant – Two different inputs may producing the same hash value. Read this MD5 vulnerabilities. In Python, we can use hashlib.md5() to generate a MD5 hash value […]
This JEP 181: Nest-Based Access Control, supports private access within nest members directly, no more via an auto-generated bridge method access$000. Furthermore, new nest APIs for validation and allowed private reflection access within nest members. P.S No need to change the code, it is a Java compiler’s optimization to remove the bridge method access. 1. […]
In Java 8, we can use StreamSupport.stream to convert an Iterator into a Stream. // Iterator -> Spliterators -> Stream Stream<String> stream = StreamSupport.stream( Spliterators.spliteratorUnknownSize( iterator, Spliterator.ORDERED) , false); Review the StreamSupport.stream method signature, it accepts a Spliterator. StreamSupport.java public static <T> Stream<T> stream(Spliterator<T> spliterator, boolean parallel) { Objects.requireNonNull(spliterator); return new ReferencePipeline.Head<>(spliterator, StreamOpFlag.fromCharacteristics(spliterator), parallel); } […]
A few of Java Iterator and ListIterator examples. 1. Iterator 1.1 Get Iterator from a List or Set, and loop over it. JavaIteratorExample1a.java package com.mkyong; import java.util.Arrays; import java.util.Iterator; import java.util.List; public class JavaIteratorExample1a { public static void main(String[] args) { /* Set<Integer> set = new HashSet<>(); set.add(1); set.add(2); set.add(3); set.add(4); set.add(5); Iterator<Integer> iterator = […]
Java 14 reached General Availability on 17 March 2020, download Java 14 here. Java 14 features. 1. JEP 305: Pattern Matching for instanceof (Preview) 2. JEP 343: Packaging Tool (Incubator) 3. JEP 345: NUMA-Aware Memory Allocation for G1 4. JEP 349: JFR Event Streaming 5. JEP 352: Non-Volatile Mapped Byte Buffers 6. JEP 358: Helpful […]
