普通单例、文艺单例、二逼单例

• 普通单例

public class Singleton {
	private static Singleton uniqueInstance = new Singleton();
	
	private Singleton(){
		
	}
	
	public static Singleton getInstance(){
		return uniqueInstance;
	}
}

• 文艺单例

public class Singleton {
	private static Singleton uniqueInstance;
	
	private Singleton(){
		
	}
	
	public static Singleton getInstance(){
		if(uniqueInstance == null){
			synchronized (Singleton.class) {
				if(uniqueInstance == null){
					uniqueInstance = new Singleton();
				}
			}
		}
		return uniqueInstance;
	}
}

•  2逼单例

public class Singleton {
	private static Singleton uniqueInstance;

	private Singleton() {

	}

	public static synchronized Singleton getInstance() {
		if (uniqueInstance == null) {
			uniqueInstance = new Singleton();
		}
		return uniqueInstance;
	}
}