I just wrote the following code as a test: public class DaemonThreadPlay { public static void main(String [] args) { Thread daemonThread = new Thread() { public void run() { while (true) { try { System.out.println(“Try block executed”); Thread.sleep(1000l); } catch (Throwable t) { t.printStackTrace(); } } } @Override public void finalize() { System.out.println(“Finalize method … Read more
If I compiled a java file in the newest JDK, would an older JVM be able to run the .class files? That depends on three things: The actual Java versions you are talking about. For instance, a 1.4.0 JVM can run code compiled by a 1.4.2 compiler, but a 1.3.x JVM cannot1. The compilation flags … Read more
-XX:PermSize specifies the initial size that will be allocated during startup of the JVM. If necessary, the JVM will allocate up to -XX:MaxPermSize.
Good lord no. Sometimes there is a possibility that something can occur in the loop that satisfies the overall requirement, without satisfying the logical loop condition. In that case, break is used, to stop you cycling around a loop pointlessly. Example String item; for(int x = 0; x < 10; x++) { // Linear search. … Read more
Most HotSpot JVM in the last year have had it on by default. This option allows references to be 32-bit in a 64-bit JVM and access close to 32 GB of heap. (more than 32-bit pointers can) (You can have near unlimited off heap memory as well). This can save a significant amount of memory … Read more
As always, check your local JVM’s specific implementation but here is a quick way to check from the command line without having to code. > java -version; java -Xmx1G -XX:+PrintFlagsFinal -Xmx2G 2>/dev/null | grep MaxHeapSize java version “1.8.0_25” Java(TM) SE Runtime Environment (build 1.8.0_25-b17) Java HotSpot(TM) 64-Bit Server VM (build 25.25-b02, mixed mode) uintx MaxHeapSize … Read more
<init> is the (or one of the) constructor(s) for the instance, and non-static field initialization. <clinit> are the static initialization blocks for the class, and static field initialization. class X { static Log log = LogFactory.getLog(); // <clinit> private int x = 1; // <init> X(){ // <init> } static { // <clinit> } }
Python (the language) doesn’t need a GIL (which is why it can perfectly be implemented on JVM [Jython] and .NET [IronPython], and those implementations multithread freely). CPython (the popular implementation) has always used a GIL for ease of coding (esp. the coding of the garbage collection mechanisms) and of integration of non-thread-safe C-coded libraries (there … Read more
Big disclaimer: I am not a GC expert/writer; all the things that are written bellow are subject to changes and some of them might be way too simplistic. Please take this with a grain of salt. I will only speak about Shenandoah, as I think I understand it; which is not a generational GC. There … Read more
String literals are interned. As of Java 7, the HotSpot JVM puts interned Strings in the heap, not permgen. Prior to java 7, hotspot put interned Strings in permgen. However, interned Strings in permgen were garbage collected. Apparently, Class objects in permgen are also collectable, so everything in permgen is collectable, though permgen collection might … Read more