android 设计模式学习

1：单例模式

//对于创建开销较大的类可使用此方法，保证全局一个实例，在程序运行过程中该类不会因新建额外对象产生开销。示例代码如下：
public class Singleton {

    private static Object    obj      = new Object();
    private static Singleton instance = null;

    private Singleton(){
    }

    public static Singleton getInstance() {
        // if already inited, no need to get lock everytime
        if (instance == null) {
            synchronized (obj) {
                if (instance == null) {
                    instance = new Singleton();
                }
            }
        }

        return instance;
    }
}

//一般般的
public class SqlManager {   

public static SqlManager sqlManager = null;
    public static SqlManager intance(Context context) {
        if (sqlManager == null) {       
        sqlManager = new SqlManager(context);    
       }       
    return sqlManager;   
    }

}