Singleton pattern: ensures that a class has only one instance and provides a global access point
1. Hungry Chinese style singleton
public class HungrySingleton {
private static HungrySingleton instance = new HungrySingleton();
private HungrySingleton() {
};
public static HungrySingleton getInstance() {
return instance;
}
}
2. Lazy Singleton
public class LazySingleton {
private static LazySingleton instance;
private LazySingleton() {
};
public static synchronized LazySingleton getInstance() {
if (null == instance) {
instance = new LazySingleton();
}
return instance;
}
}
3. Double check lock implementation
public class DoubleCheckedSingleton {
private volatile static DoubleCheckedSingleton instance;
private DoubleCheckedSingleton() {
};
public static DoubleCheckedSingleton getInstance() {
if (null == instance) {
synchronized(DoubleCheckedSingleton.class) {
if (null == instance) {
instance = new DoubleCheckedSingleton();
}
}
}
return instance;
}
}
4. Static inner class implementation
public class Singleton {
private Singleton() {
};
public static Singleton getInstance() {
return SingletonHolder.singleton;
}
private static class SingletonHolder {
private static final Singleton singleton = new Singleton();
}
}
5. Implementation by enumeration
public class EnumSingleton {
public enum ResourceInstance {
INSTANCE;
private Resource resource;
ResourceInstance() {
this.resource = new Resource();
}
public Resource getResource() {
return this.resource;
}
}
}
class Resource {
}