final

In a Java program, I have multiple subclasses inheriting from a parent (which is abstract). I wanted to express that every child should have a member that is set once only (which I was planning to do from the constructor). My plan was to code s.th. like this: public abstract class Parent { protected final String birthmark; } public class Child extends Parent { public Child(String s) { this.birthmark = s; } } However, this seems to not please the Java gods. In the parent class, I get the message that birthmark "might not have been initialized", in the child class I get "The final field

When I am just trying to do some program in Java .I try to use final variable,I know that final variable must be initialized at the time of declaration, but inside the main method it accepts the final variable with out initialization. I don't know what's the reason.Can any one tell me the reason. Thank you code: class name { final int b; //here shows error public static void main(String args[]) { final int a; // here no error... why? System.out.println("hai"); } } For instance variable level A final variable can be initialized only once. A final variable at class level must be initialized

I have this piece of code that loads Properties from a file: class Config { val properties: Properties = { val p = new Properties() p.load(Thread.currentThread().getContextClassLoader.getResourceAsStream("props")) p } val forumId = properties.get("forum_id") } This seems to be working fine. I have tried moving the initialization of properties into another val, loadedProperties , like this: class Config { val properties: Properties = loadedProps val forumId = properties.get("forum_id") private val loadedProps = { val p = new Properties() p.load(Thread.currentThread().getContextClassLoader

If I have a variable int x = 1 , say, and I declare a runnable in the main thread, and I want to pass x to the runnable's run() method, it must be declared final . Why? final int x = 0;//<----must be final... private class myRun implements Runnable { @Override public void run() { x++;// } } Because if they are able to be changed, it could cause a lot of problems, consider this: public void count() { int x; new Thread(new Runnable() { public void run() { while(x < 100) { x++; try { Thread.sleep(1000); }catch(Exception e){} } } }).start(); // do some more code... for(x = 0;x < 5;x++) for(int y =

To my understanding, the following code should have printed true . However, when I ran this code it is printing false . From Java docs of Anonymous Classes 15.9.5. : An anonymous class is always implicitly final public class Test { public static void main(String args[]) { Object o = new Object() { }; System.out.println("Annonymous class is final: " + Modifier.isFinal(o.getClass().getModifiers())); } } Can some one please help me understand this behavior. Note that the wording in the JLS of that particular section has changed significantly since then. It now (JLS 11) reads: 15.9.5. Anonymous

I tried to understand the behavior of initialization order when static fields are initialized with a reference to the same enclosing class object. public class Test { static final Test t=new Test(); static int a=5; Test(){ System.out.println("a="+a); } public static void main(String[] args) { new Test(); } } Output of above piece of code is: a=0 a=5 If I modify variable a to anything else other than plain static : static final a=5; a=5; final a=5; The output is: a=5 a=5 Why is this behavior? Note that the output is a=5 & a=5 even when both t & a are declared as static final in which case t