@Component Preferable for component scanning and automatic wiring. When should you use @Bean? Sometimes automatic configuration is not an option. When? Let’s imagine that you want to wire components from 3rd-party libraries (you don’t have the source code so you can’t annotate its classes with @Component), so automatic configuration is not possible. The @Bean annotation … Read more
To run a single test method in Maven, you need to provide the command as: mvn test -Dtest=TestCircle#xyz test where TestCircle is the test class name and xyz is the test method. Wild card characters also work; both in the method name and class name. If you’re testing in a multi-module project, specify the module … Read more
There’s no built in type for ConcurrentHashSet because you can always derive a set from a map. Since there are many types of maps, you use a method to produce a set from a given map (or map class). Prior to Java 8, you produce a concurrent hash set backed by a concurrent hash map, … Read more
To safely remove from a collection while iterating over it you should use an Iterator. For example: List<String> names = …. Iterator<String> i = names.iterator(); while (i.hasNext()) { String s = i.next(); // must be called before you can call i.remove() // Do something i.remove(); } From the Java Documentation : The iterators returned by … Read more
You can use the java.lang.instrument package. Compile and put this class in a JAR: import java.lang.instrument.Instrumentation; public class ObjectSizeFetcher { private static Instrumentation instrumentation; public static void premain(String args, Instrumentation inst) { instrumentation = inst; } public static long getObjectSize(Object o) { return instrumentation.getObjectSize(o); } } Add the following to your MANIFEST.MF: Premain-Class: ObjectSizeFetcher Use … Read more
Fun fact: The original snippet posted here was the most copied Java snippet of all time on Stack Overflow, and it was flawed. It was fixed, but it got messy. Full story in this article: The most copied Stack Overflow snippet of all time is flawed! Source: Formatting byte size to human readable format | … Read more
Check these out: http://commons.apache.org/cli/ http://www.martiansoftware.com/jsap/ Or roll your own: http://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html For instance, this is how you use commons-cli to parse 2 string arguments: import org.apache.commons.cli.*; public class Main { public static void main(String[] args) throws Exception { Options options = new Options(); Option input = new Option(“i”, “input”, true, “input file path”); input.setRequired(true); options.addOption(input); Option … Read more
The issue is because of Java version mismatch. Referring to the JVM specification the following are the major versions of classfiles for use with different versions of Java. (As of now, all versions support all previous versions.) Java SE version Major version 1.0.2 45 1.1 45 (Not a typo, same version) 1.2 46 1.3 47 … Read more
JavaBeans A JavaBean is a class that follows the JavaBeans conventions as defined by Sun. Wikipedia has a pretty good summary of what JavaBeans are: JavaBeans are reusable software components for Java that can be manipulated visually in a builder tool. Practically, they are classes written in the Java programming language conforming to a particular … Read more
Here is a better and less tightly coupled way to implement an OnClickListener for a RecyclerView. Snippet of usage: RecyclerView recyclerView = findViewById(R.id.recycler); recyclerView.addOnItemTouchListener( new RecyclerItemClickListener(context, recyclerView ,new RecyclerItemClickListener.OnItemClickListener() { @Override public void onItemClick(View view, int position) { // do whatever } @Override public void onLongItemClick(View view, int position) { // do whatever } }) … Read more