May I make a singleton pattern like this

Question

as well know, singleton pattern in java always like the codes below:
public class ClassicSingleton {
private static ClassicSingleton instance = null;
protected ClassicSingleton() {
// Exists only to defeat instantiation.
public static ClassicSingleton getInstance() {
if(instance == null) {
instance = new ClassicSingleton();
return instance;
but, when I read the java non-static initialization block section, I had an new idea about a this pattern. how about like this:
public class ClassicSingleton {
     private static ClassicSingleton instance = null;
     protected ClassicSingleton() {
          // Exists only to defeat instantiation.
     static{
          instance = new ClassicSingleton();
     public static ClassicSingleton getInstance() {
          return instance;
or like this
public class ClassicSingleton {
     private static ClassicSingleton instance = null;
     protected ClassicSingleton() {
          // Exists only to defeat instantiation.
          instance = new ClassicSingleton();
     public static ClassicSingleton getInstance() {
          return instance;
could anybody here tell me what's the different? thanks.

Answer 1

I usually do something like this:
public class ClassicSingleton {
  private static ClassicSingleton instance = new ClassicSingleton();
  private ClassicSingleton() {
    try{
      /* Construction logic here. */
    }catch(Exception e){
      /* Something bad happened, decide what to do, like set a flag indicating singleton isn't valid. */
  public static ClassicSingleton getInstance() {
    return instance;
}