Calling a Classes constrictor explicitly with out editing the Class

Question

Hi All,
I am looking for a way to call the a Classes static constructor of a class so that the static fields get initialized. Here is some pseudo code to illustrate
class Singleton {
    private static instance = new Singleton();
    private Map map = new HashMap();
    boolean obtainedKey = false;
    private Singleton() {
        //populate map code
    public Singleton getInstance() {
        return instance;
   public Object getVal(String key) {
       obtainedKey = true;
       return map.get(key);
  public getObtainedKey() {
     return obtainedKey;
class MyClass {
     static Singleton sing = Singleton.getInstance();
     static Object objVal = sing getVal.get("key");
public static void main(String [] args)  {
      Singleton singMain = Singleton.getInstance();
      MyClass.*SOME_METHOD_ALREADY_IN_JAVA*;
      assert(singMain.getObtainedKey() == true);
} One solution is to add a method ;
static void init() {}; to the class MyClass and then to call this method,
However I would like to find a method somewhere in the java library so I don't have to write a init method.

Answer 1

I think you really should re-think your architecture if it depends on such strange loops (and personally I've had very bad experiences with static initializer blocks, especially those that can fail).
But curiousity got the better of me and I dug into the JVM spec. In �2.11 (http://java.sun.com/docs/books/jvms/second_edition/html/Concepts.doc.html#32316) it says
Any static initializers declared in a class are executed when the class is initialized (�2.17.4) and, together with any field initializers (�2.9.2) for class variables, may be used to initialize the class variables of the class (�2.17.4).And in �2.17.4 (http://java.sun.com/docs/books/jvms/second_edition/html/Concepts.doc.html#19075) it says
Initialization of a class consists of executing its static initializers (�2.11) and the initializers for static fields (�2.9.2) declared in the class. Initialization of an interface consists of executing the initializers for fields declared in the interface (�2.13.3.1).
Before a class or interface is initialized, its direct superclass must be initialized, but interfaces implemented by the class need not be initialized. Similarly, the superinterfaces of an interface need not be initialized before the interface is initialized.
A class or interface type T will be initialized immediately before one of the following occurs:
* T is a class and an instance of T is created.
* T is a class and a static method of T is invoked.
* A nonconstant static field of T is used or assigned. A constant field is one that is (explicitly or implicitly) both final and static, and that is initialized with the value of a compile-time >constant expression. A reference to such a field must be resolved at compile time to a copy of the compile-time constant value, so uses of such a field never cause initialization.
Invocation of certain methods in library classes (�3.12) also causes class or interface initialization. See the Java 2 platform's class library specifications (for example, class Class and package java.lang.reflect) for details.So if you don't want to create and instance or add a method then you can only use (read) or assign a nonconstant static field (the field initialized by the static block should be fine).
The library functions above are not required to initialize the class, so that won't be much help.