How to force a class to be initialised? [closed]

Question

What is the best and cleanest way to do this? Specifically, I need some code in a static initializer block to run in that class, but I'd like to make this as clean-looking as possible.

Answer 1

Loading != Initialization.

You want your class to be initialized (this is when static blocks executed, among other things).

An excerpt from the Java Language Specification says:

A class or interface type T will be initialized immediately before the first occurrence of >any one of the following:

• T is a class and an instance of T is created.
• T is a class and a static method declared by T is invoked.
• A static field declared by T is assigned.
• A static field declared by T is used and the field is not a constant variable (§4.12.4).
• T is a top-level class, and an assert statement (§14.10) lexically nested within T is executed.

Invocation of certain reflective methods in class Class and in package java.lang.reflect also causes class or interface initialization. A class or interface will not be initialized under any other circumstance.

Doh, anovstrup, already said it: Just make an empty static function called init. Be sure to document that well... I personally can't see any use case for this in the context of well formed code though.

Answer 2

You can use the following code to force initialization of a class:

//... Foo.class ...          //OLD CODE ... forceInit(Foo.class) ... //NEW CODE  /**  * Forces the initialization of the class pertaining to   * the specified <tt>Class</tt> object.   * This method does nothing if the class is already  * initialized prior to invocation.  *  * @param klass the class for which to force initialization  * @return <tt>klass</tt>   */ public static <T> Class<T> forceInit(Class<T> klass) {     try {         Class.forName(klass.getName(), true, klass.getClassLoader());     } catch (ClassNotFoundException e) {         throw new AssertionError(e);  // Can't happen     }     return klass; }