Java init method

Question

What's a good way to make sure an init method is invoked in java? The alternatives I see are

• Don't test it, let the method fail by itself, likely by a NullPointerException
• Test if method was initialized or throw

public void foo() {
     if (!inited) {
         throw new IllegalArgumentException("not initalized");
     }
     ...
}

• Delagate

public void foo() {
     if (!inited) {
         throw new IllegalArgumentException("not initalized");
     }
     fooInternal();
}

private void fooInternal(){ ... };

• Always init, and make init a noop otherwise

public void foo() {
     init();
     ...
}
public void init() {
     if(!inited) {
         ...
     }
}

• Silently init

public void foo() {
     if (!inited) {
         init();
     }
     ...
}

Most of these approaches are very verbose and decreases overall readability.

Answer 1

If initialisation is part of the usage contract throw IllegalStateException because the client of the class has not caused it to transition to the correct "initialised" state…

Whether you initialise upon creation or not depends on how it is to be used. For instance if a possibility is that it may be used by a Spring ApplicationContext then you'll want to defer initialisation.

Answer 2

Most of the time you want to fail fast so choose the mechanism that helps you fail fast based upon the container your application is executing in. For e.g if a web container then may be you initialize it during creation of servlet context. Moreover, I am not sure why the below is verbose. It is simple, clear and explicit on the intent.

public void foo() {
     if (!inited) {
         init();
     }
     ...
}

Answer 3

Call init(); whithin an initializer block, that way every constructor call will also execute init();.