设计模式（单例）

public class DataSingleton {
    private static DataSingleton instance;
    
    public DataSingleton(){
        System.out.println("DataSingleton created");
    }
    
    //注意保证线程安全
    public static synchronized DataSingleton getInstance(){
        if(null == instance){
            instance = new DataSingleton();
        }
        
        return instance;
    }
}