This message means that for some reason the garbage collector is taking an excessive amount of time (by default 98% of all CPU time of the process) and recovers very little memory in each run (by default 2% of the heap). This effectively means that your program stops doing any progress and is busy running … Read more
You place the function in the “companion object”. So the java code like this: class Foo { public static int a() { return 1; } } will become class Foo { companion object { fun a() : Int = 1 } } You can then use it from inside Kotlin code as Foo.a(); But from … Read more
Using java.io.File: File f = new File(filePathString); if(f.exists() && !f.isDirectory()) { // do something }
Go to File > Settings > Build, Execution, Deployment > Compiler > Java Compiler If on a Mac, it’s under Intellij IDEA > Preferences… > Build, Execution, Deployment > Java Compiler Change Target bytecode version to 1.8 of the module that you are working for. If you are using Maven Add the compiler plugin to … Read more
Tips about writing micro benchmarks from the creators of Java HotSpot: Rule 0: Read a reputable paper on JVMs and micro-benchmarking. A good one is Brian Goetz, 2005. Do not expect too much from micro-benchmarks; they measure only a limited range of JVM performance characteristics. Rule 1: Always include a warmup phase which runs your … Read more
You need a 64-bit trio: 64-bit OS 64-bit Java 64-bit Eclipse
In Java 8: List<String> newList = Stream.concat(listOne.stream(), listTwo.stream()) .collect(Collectors.toList()); Java 16+: List<String> newList = Stream.concat(listOne.stream(), listTwo.stream()).toList();
One possible (and common) use is when you have some object that is not thread-safe, but you want to avoid synchronizing access to that object (I’m looking at you, SimpleDateFormat). Instead, give each thread its own instance of the object. For example: public class Foo { // SimpleDateFormat is not thread-safe, so give one to … Read more
You can use Apache Commons IO to handle this and similar tasks. The IOUtils type has a static method to read an InputStream and return a byte[]. InputStream is; byte[] bytes = IOUtils.toByteArray(is); Internally this creates a ByteArrayOutputStream and copies the bytes to the output, then calls toByteArray(). It handles large files by copying the … Read more
There are several ways to simulate optional parameters in Java: Method overloading. void foo(String a, Integer b) { //… } void foo(String a) { foo(a, 0); // here, 0 is a default value for b } foo(“a”, 2); foo(“a”); One of the limitations of this approach is that it doesn’t work if you have two … Read more