This article shows you five examples to convert a string into a binary string representative or vice verse. Convert String to Binary – Integer.toBinaryString Convert String to Binary – Bit Masking Convert Binary to String – Integer.parseInt Convert Unicode String to Binary. Convert Binary to Unicode String. 1. Convert String to Binary – Integer.toBinaryString The […]
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 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 […]
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 […]
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(), […]
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 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. […]
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 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 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 […]
This JEP 181: Nest-Based Access Control, supports private access within nest members directly, no more via an auto-generated bridge method access$000. Furthermore, new nest APIs for validation and allowed private reflection access within nest members. P.S No need to change the code, it is a Java compiler’s optimization to remove the bridge method access. 1. […]
A few of Java Iterator and ListIterator examples. 1. Iterator 1.1 Get Iterator from a List or Set, and loop over it. JavaIteratorExample1a.java package com.mkyong; import java.util.Arrays; import java.util.Iterator; import java.util.List; public class JavaIteratorExample1a { public static void main(String[] args) { /* Set<Integer> set = new HashSet<>(); set.add(1); set.add(2); set.add(3); set.add(4); set.add(5); Iterator<Integer> iterator = […]
Java 14 reached General Availability on 17 March 2020, download Java 14 here. Java 14 features. 1. JEP 305: Pattern Matching for instanceof (Preview) 2. JEP 343: Packaging Tool (Incubator) 3. JEP 345: NUMA-Aware Memory Allocation for G1 4. JEP 349: JFR Event Streaming 5. JEP 352: Non-Volatile Mapped Byte Buffers 6. JEP 358: Helpful […]
Typically, we use Arrays.asList or the new Java 9 List.of to create a List. However, both methods return a fixed size or immutable List, it means we can’t modify it, else it throws UnsupportedOperationException. JavaListExample.java package com.mkyong; import java.util.Arrays; import java.util.List; public class JavaListExample { public static void main(String[] args) { // immutable list, cant […]
The java.util.Arrays$ArrayList is a nested class inside the Arrays class. It is a fixed size or immutable list backed by an array. Arrays.java public static <T> List<T> asList(T… a) { return new ArrayList<>(a); } /** * @serial include */ private static class ArrayList<E> extends AbstractList<E> implements RandomAccess, java.io.Serializable { private static final long serialVersionUID = […]
This example shows you how to display a percentage % in String.format. JavaStringFormat1.java package com.mkyong; public class JavaStringFormat1 { public static void main(String[] args) { String result = String.format("%d%", 100); System.out.println(result); } } Output Exception in thread "main" java.util.UnknownFormatConversionException: Conversion = ‘%’ at java.base/java.util.Formatter.checkText(Formatter.java:2732) at java.base/java.util.Formatter.parse(Formatter.java:2718) at java.base/java.util.Formatter.format(Formatter.java:2655) at java.base/java.util.Formatter.format(Formatter.java:2609) at java.base/java.lang.String.format(String.java:2897) Solution To display […]
This article shows you how to use the JDK1.5 String.format() and Apache Common Lang to left or right pad a String in Java. 1. String.format By default, the String.format() fills extra with spaces \u0020. Normally, we use replace() to pad with other chars, but it will replace the spaces in between the given string. JavaPadString1.java […]
This article shows you how to format a string in Java, via String.format(). Here is the summary. Conversion Category Description %b, %B general true of false %h, %H general hash code value of the object %s, %S general string %c, %C character unicode character %d integral decimal integer %o integral octal integer, base 8 %x, […]
Both remainder and modulo are two similar operations; they act the same when the numbers are positive but much differently when the numbers are negative. In Java, we can use Math.floorMod() to describe a modulo (or modulus) operation and % operator for the remainder operation. See the result: | rem & +divisor| rem & -divisor […]
On Ubuntu, we can add JAVA_HOME environment variable in /etc/environment file. Note /etc/environment system-wide environment variable settings, which means all users use it. It is not a script file, but rather consists of assignment expressions, one per line. We need admin or sudo to modify this it. Further Reading Ubuntu – EnvironmentVariables 1. JAVA_HOME 1.1 […]
In Java, byte is an 8-bit signed (positive and negative) data type, values from -128 (-2^7) to 127 (2^7-1). For unsigned byte, the allowed values are from 0 to 255. Java doesn’t have unsigned bytes (0 to 255). To make an unsigned byte, we can cast the byte into an int and mask (bitwise and) […]
This article shows how to install Java JDK on macOS, Homebrew package manager, manual installation, and switch between different JDK versions. Tested with macOS 11 Big Sur Homebrew 2.7.4 JDK 8, 14, 16, 16 (AdoptOpenJDK and OpenJDK) Topics Homebrew install latest Java (OpenJDK) on macOS Homebrew install Java 8 (OpenJDK) on macOS Homebrew install a […]
This article shows how to parse JSON Array using Gson. Table of contents: 1. Download Google Gson 2. Parse JSON Array using Gson 3. Parse JSON Array of Object Array using Gson 4. JSON array contains array of object 5. Unusual JSON array contains array of string 6. Download Source Code 7. References P.S Tested […]
In Java, we can use LinkedHashMap to keep the insertion order. P.S HashMap does not guarantee insertion order. 1. HashMap Generate a HashMap, UUID as key, index 0, 1, 2, 3, 4… as value. JavaHashMap.java package com.mkyong.samples; import java.util.HashMap; import java.util.Map; import java.util.UUID; import java.util.stream.IntStream; public class JavaHashMap { public static void main(String[] args) { […]
The below program is a typical Java trap, and also a popular Java interview question. It has no compiler error or warning but running very slow. Can you spot the problem? JavaSum.java package com.mkyong; import java.time.Duration; import java.time.Instant; public class JavaSum { public static void main(String[] args) { Instant start = Instant.now(); Long total = […]
In Java, we can use Locale.setDefault() to change the JVM default locale. JavaLocaleExample.java package com.mkyong.locale; import java.util.Locale; public class JavaLocaleExample { public static void main(String[] args) { // get jvm default locale Locale defaultLocale = Locale.getDefault(); System.out.println(defaultLocale); // set jvm locale to china Locale.setDefault(Locale.CHINA); // or like this //Locale.setDefault(new Locale("zh", "cn"); Locale chinaLocale = Locale.getDefault(); […]
