Good little tiny post.

public class StaticClass {
static {
Object o = null;
o.toString();
}
public static void someMethod() {}
}

and using it in the following way:
try {
StaticClass.someMethod();
} catch (Throwable t) {
t.printStackTrace();
}
try {
StaticClass.someMethod();
} catch (Throwable t) {
t.printStackTrace();
}

you get an ExceptionInInitializerError when invoking it for the first time(caused by a NullPointerException). So you get the information you need to fix the problem.

But on the second invocation you get a java.lang.NoClassDefFoundError: StaticClass. And this does not help you at all.

So if you happen to miss the first exception (which might happen if you have a lot of logging) you will have a big problem finding out, what actually went wrong.

So imho static initializers should be avoided as much as possible.

If you change the StaticClass to:

public class StaticClass {
private StaticClass instance;

public StaticClass() {
Object o = null;
o.toString();
}
public void someMethod() {}

public synchronized StaticClass getInstance() {
if (instance == null) {
instance = new StaticClass()
}
return instance;
}
}

You avoid that problem. Also the code will recover if the failure is a temporary one (”file not found” or something like that). In the first version you have to restart the VM to fix the problem.