I am trying to write a Singleton Lazy Loading Pattern. Here is the class:
public class IMDBLookup {
private static class LazyLoad {
private static final IMDBLookup IMDB_LOOKUP;
static {
IMDB_LOOKUP = new IMDBLookup();
}
}
public static IMDBLookup getInstance() {
return IMDBLookup.LazyLoad.IMDB_LOOKUP;
}
}
I am wondering whether or not I am doing it in a right way?
Thanks in advance.
I prefer to use enum for simplicity.
public enum IMDBLookup {
INSTANCE;
// add fields and methods here.
}
That is correct. You may want to simplify the inner (holder) class as private static final IMDBLookup IMDB_LOOKUP = new IMDBLookup(); for brevity (to get rid of the static initializer block.)
public class IMDBLookup {
private IMDBLookup(){
// without this I do not get why is it a singleton
// anyone could create instances of your class by the thousands
}
private static class LazyLoad {
private static final IMDBLookup IMDB_LOOKUP;
static {
IMDB_LOOKUP = new IMDBLookup();
}
}
public static IMDBLookup getInstance() {
return IMDBLookup.LazyLoad.IMDB_LOOKUP;
}
}
and you should probably use an enum (not completely sure I do this right)
public class IMDBLookup {
private IMDBLookup(){
}
private static enum LazyLoad {
IMDB_LOOKUP_INSTANCE;
private static final IMDB_LOOKUP = new IMDBLookup();
}
public static IMDBLookup getInstance() {
return LazyLoad.IMDB_LOOKUP_INSTANCE.IMDB_LOOKUP;
}
}
The advice you to think about clone & serialize
import java.io.Serializable;
public class DBConnectionInner implements Cloneable, Serializable {
private static final long serialVersionUID = 1173438078175185035L;
@Override
protected Object clone() throws CloneNotSupportedException {
return new CloneNotSupportedException("CLONE NOT SUPPORT FOR SINGTELTON");
}
protected Object readResolve() {
return getInstance();
}
private DBConnectionInner() {}
static DBConnectionInner getInstance() {
System.out.println("DBConnectionInner getInstance");
return LazyInit.instance;
}
public static class LazyInit {
private static final DBConnectionInner instance = new DBConnectionInner();
}
}
