A man may be disposed to envy, or to violence of emotion, or to regard truth or life highly, or to be intolerant of frustration. Whatever it is that causes him to be so disposed, I shall call his state of mind at the time he is so disposed, his ‘disposition’. The propositions I use as premises are all in this sense dispositions. But, as I write this, it is brought home to me how difficult it is to verbalize with accuracy without losing meaning, or to write meaningfully without losing accuracy.
‘A disposition.’ Does this mean something in the psyche? Are there such things as dispositions? At once a problem is, what does one mean by ‘thing’? He is disposed to be envious; he has an envious disposition; his disposition is to be envious. All these sentences mean something. It does not seem unreasonable to claim that there is such a thing as an envious disposition. Very well: then there are envious dispositions, truthful dispositions, narcissistic dispositions, violent dispositions, loving dispositions—to take instances from the premises I have chosen. Since I want to say that there are such things, that is to say, things in actuality, in reality, which are represented by the word, ‘disposition’, it is essential always to use the word in such a way that the reader will be correct in assuming that I mean what I meant on the previous occasion, that there is in reality something that is represented by the word, ‘disposition’.
In this chapter, you will learn Android’s capabilities by looking at the big features it offers. We’ll give you a high-level overview of what activities are, how intents work, when and how to use services, how to use broadcast receivers and content providers to make your app scale, and much more.
By “main building blocks,” we refer to the pieces of an application that Android offers you to put together into an Android app. When you start thinking about your application, it is good to take a top-down approach. For instance, most programmers design applications in terms of screens, features, and the interactions between them. You start with a conceptual drawing, something that you can represent in terms of “lines and circles.” This approach to application development helps you see the big picture—how the components fit together and how it all makes sense.
By the end of this chapter, you will understand the main Android components for building applications. You should conceptually know when you’d use what component. You will also see how these components relate to a real-world application.
This chapter is about variables that have special meanings to Perl.
Most of the punctuational names have reasonable mnemonics or analogs in one
of the shells (or both). But if you want to use long variable names as
synonyms, just say:
at the top of your program. This aliases all the short names to long names in the current
package. Some of these variables even have medium names, generally borrowed
from awk. Most people eventually settle
on using the short names, at least for the more commonly used variables.
Throughout this book, we consistently refer to the short names, but we also
often mention the long names (in parentheses) so that you can look them up
easily in this chapter.
The semantics of these variables can be quite magical. (To create your
own magic, see Chapter14.) A few of these variables are
read-only. If you try to assign values to them, an exception will be
In what follows, well first provide a concise listing of the
variables and functions for which Perl assigns a special meaning, grouped by
type, so you can look up variables when youre not sure of the proper name.
Then well explain all of the variables alphabetically under their proper
name (or their least improper name).