#вопросы_с_собеседований
Как создать потокобезопасный Singleton?
• Static field
class Singleton {
public static final Singleton INSTANCE = new Singleton();
}
• Enum
enum Singleton {
INSTANCE;
}
• Synchronized Accessor
class Singleton {
private static Singleton instance;
public static synchronized Singleton getInstance() {
if (instance == null) {
instance = new Singleton();
}
return instance;
}
}
• Double Checked Locking & volatile
class Singleton {
private static volatile Singleton instance;
public static Singleton getInstance() {
Singleton localInstance = instance;
if (localInstance == null) {
synchronized (Singleton.class) {
localInstance = instance;
if (localInstance == null) {
instance = localInstance = new Singleton();
}
}
}
return localInstance;
}
}
• On Demand Holder Idiom
public class Singleton {
public static class SingletonHolder {
public static final Singleton HOLDER_INSTANCE = new Singleton();
}
public static Singleton getInstance() {
return SingletonHolder.HOLDER_INSTANCE;
}
}
