单例模式(懒汉式和饿汉式)

public class Singleton {

private volatile static Singleton mSingleton;

private Singleton() {}

public static Singleton getInstance() {

if (mSingleton == null) {

synchronized (Singleton.class) {

if (mSingleton == null) {

mSingleton = new Singleton();
}
}
}
return mSingleton;
}
}

public class Singleton {

private static Singleton mSingleton = new Singleton();

private Singleton() {}

public static Singleton getInstance() {

return mSingleton;
}
}