5000字英文文献翻译

时间：2016-11-10 11:19:55 来源：免费论文网

篇一：5000字英文文献翻译

沈阳建筑大学

毕业论文

外文及翻译

原文题目

学院专业班级信息与控制工程学院计算机08-1

学生姓名 XXX 性别 X

指导教师 XXX 职称 XX

年月

日

外文及翻译

英语原文 Android Application Fundamentals

Once installed on a device, each Android application lives in its own security sandbox: ? The Android operating system is a multi-user Linux system in which each

application is a different user. ? By default, the system assigns each application a unique Linux user ID (the ID is

used only by the system and is unknown to the application). The system sets

permissions for all the files in an application so that only the user ID assigned to that

application can access them.

? Each process has its own virtual machine (VM), so an application's code runs in

isolation from other applications.

? By default, every application runs in its own Linux process. Android starts the

process when any of the application's components need to be executed, then shuts

down the process when it's no longer needed or when the system must recover

memory for other applications.

In this way, the Android system implements the principle of least privilege. That is, each application, by default, has access only to the components that it requires to do its work and no more. This creates a very secure environment in which an application cannot access parts of the system for which it is not given permission.

However, there are ways for an application to share data with other applications and for an application to access system services:

? It's possible to arrange for two applications to share the same Linux user ID, in which

case they are able to access each other's files. To conserve system resources,

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applications with the same user ID can also arrange to run in the same Linux process

and share the same VM (the applications must also be signed with the same

certificate).

? An application can request permission to access device data such as the user's

contacts, SMS messages, the mountable storage (SD card), camera, Bluetooth, and

more. All application permissions must be granted by the user at install time.

That covers the basics regarding how an Android application exists within the system. The rest of this document introduces you to: ? The core framework components that define your application.

? The manifest file in which you declare components and required device features for

your application.

? Resources that are separate from the application code and allow your application to

gracefully optimize its behavior for a variety of device configurations.

Application Components

Application components are the essential building blocks of an Android application. Each component is a different point through which the system can enter your application. Not all components are actual entry points for the user and some depend on each other, but each one exists as its own entity and plays a specific role—each one is a unique building block that helps define your application's overall behavior.

There are four different types of application components. Each type serves a distinct purpose and has a distinct lifecycle that defines how the component is created and destroyed.

Here are the four types of application components:

Activities

An activity represents a single screen with a user interface. For example, an email application might have one activity that shows a list of new emails, another activity to compose an email, and another activity for reading emails. Although the activities work together to form a cohesive user experience in the email application, each one is independent of the others. As such, a different application can start any one of these activities (if the email application allows it). For example, a camera application can start the activity in the email application that composes new mail, in order for the user

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to share a picture.

An activity is implemented as a subclass of Activity and you can learn more about it in the Activities developer guide.

Services

A service is a component that runs in the background to perform long-running operations or to perform work for remote processes. A service does not provide a user interface. For example, a service might play music in the background while the user is in a different application, or it might fetch data over the network without blocking user interaction with an activity. Another component, such as an activity, can start the service and let it run or bind to it in order to interact with it.

A service is implemented as a subclass of Service and you can learn more about it in the Services developer guide. Content providers

A content provider manages a shared set of application data. You can store the data in the file system, an SQLite database, on the web, or any other persistent storage location your application can access. Through the content provider, other applications can query or even modify the data (if the content provider allows it). For example, the Android system provides a content provider that manages the user's contact information. As such, any application with the proper permissions can query part of the content provider (such as ContactsContract.Data) to read and write information about a particular person.

Content providers are also useful for reading and writing data that is private to your application and not shared. For example, the Note Pad sample application uses a content provider to save notes.

A content provider is implemented as a subclass of ContentProvider and must implement a standard set of APIs that enable other applications to perform transactions. For more information, see the Content Providers developer guide.

Broadcast receivers

A broadcast receiver is a component that responds to system-wide broadcast

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announcements. Many broadcasts originate from the system—for example, a broadcast announcing that the screen has turned off, the battery is low, or a picture was captured. Applications can also initiate broadcasts—for example, to let other applications know that some data has been downloaded to the device and is available for them to use. Although broadcast receivers don't display a user interface, they may create a status bar notification to alert the user when a broadcast event occurs. More commonly, though, a broadcast receiver is just a "gateway" to other components and is intended to do a very minimal amount of work. For instance, it might initiate a service to perform some work based on the event.

A broadcast receiver is implemented as a subclass of BroadcastReceiver and each broadcast is delivered as an Intent object. For more information, see theBroadcastReceiver class.

A unique aspect of the Android system design is that any application can start another application’s component. For example, if you want the user to capture a photo with the device camera, there's probably another application that does that and your application can use it, instead of developing an activity to capture a photo yourself. You don't need to incorporate or even link to the code from the camera application. Instead, you can simply start the activity in the camera application that captures a photo. When complete, the photo is even returned to your application so you can use it. To the user, it seems as if the camera is actually a part of your application.

When the system starts a component, it starts the process for that application (if it's not already running) and instantiates the classes needed for the component. For example, if your application starts the activity in the camera application that captures a photo, that activity runs in the process that belongs to the camera application, not in your application's process.

Therefore, unlike applications on most other systems, Android applications don't have a single entry point (there's no main() function, for example).

Because the system runs each application in a separate process with file permissions that restrict access to other applications, your application cannot directly activate a component from another application. The Android system, however, can. So, to activate a component in another application, you must deliver a message to the system that specifies your intent to start a particular component. The system then activates the component for you.

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篇二：毕业论文5000字英文文献翻译(c++)

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安徽工业大学毕业设计（论文）说明书

英文翻译

英语原文：

. Introducing Classes

The only remaining feature we need to understand before solving our bookstore problem is how to write a data structure to represent our transaction data. In C++ we define our own data structure by defining a class. The class mechanism is one of the most important features in C++. In fact, a primary focus of the design of C++ is to make it possible to define class types that behave as naturally as the built-in types themselves. The library types that we've seen already, such as istream and ostream, are all defined as classesthat is,they are not strictly speaking part of the language.

Complete understanding of the class mechanism requires mastering a lot of information. Fortunately, it is possible to use a class that someone else has written without knowing how to define a class ourselves. In this section, we'll describe a simple class that we canuse in solving our bookstore problem. We'll implement this class in the subsequent chapters as we learn more about types,expressions, statements, and functionsall of which are used in defining classes.

To use a class we need to know three things:What is its name? Where is it defined?

What operations does it support?

For our bookstore problem, we'll assume that the class is named Sales_item and that it is defined in a header named Sales_item.h.The Sales_item Class

The purpose of the Sales_item class is to store an ISBN and keep track of the number of copies sold, the revenue, and average sales price for that book. How these data are stored or computed is not our concern. To use a class, we need not know anything about how it is implemented. Instead, what we need to know is what operations the class provides.

As we've seen, when we use library facilities such as IO, we must include the associated headers. Similarly, for our own classes, we must make the definitions associated with the class available to the compiler. We do so in much the same way. Typically, we put the class definition into a file. Any program that wants to use our class must include that file.

Conventionally, class types are stored in a file with a name that, like the name of a program source file, has two parts: a file name and a file suffix. Usually the file name is the same as the class defined in the header. The suffix usually is .h, but some programmers use .H, .hpp, or .hxx. Compilers usually aren't picky about header file names, but IDEs

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安徽工业大学毕业设计（论文）说明书

sometimes are. We'll assume that our class is defined in a file named Sales_item.h.Operations on Sales_item Objects

Every class defines a type. The type name is the same as the name of the class. Hence, our Sales_item class defines a type named

Sales_item. As with the built-in types, we can define a variable of a class type. When we write "Sales_item item" we are saying that item is an object of type Sales_item. We often contract the phrase "an object of type Sales_item" to"aSales_ item object" or even more simply to "a Sales_item."

In addition to being able to define variables of type Sales_item, we can perform the following operations on Sales_item objects:

Use the addition operator, +, to add two Sales_items,Use the input operator, << to read a Sales_item object,Use the output operator, >> to write a Sales_item object,

Use the assignment operator, =, to assign one Sales_item object to another,

Call the same_isbn function to determine if two Sales_items refer to the same book.Classes are central to most C++ programs: Classes let us define our own types that are customizedfor the problems we need to solve, resulting in applications that are easier to write and understand.Well-designed class types can be as easy to use as the built-in types.A class defines data and function members: The data members store the state associated with objectsof the class type, and the functions perform operations that give meaning to the data. Classeslet us separate implementation and interface. The interface specifies the operations that the classsupports. Only the implementor of the class need know or care about the details of the implementation. This separation reduces the bookkeeping aspects that make programming tedious anderror-prone.

Class types often are referred to as abstract data types. An abstract data type treats the data(state) and operations on that state as a single unit. We can think abstractly about what the classd oes, rather than always having to be aware of how the class operates. Abstract data types arefundamental to both object-oriented and generic programming.

Data abstraction is a programming (and design) technique that relies on the separation of interfaceand implementation. The class designer must worry about how a class is implemented, but programmersthat use the class need not know about these details. Instead, programmers who use a type need to know only the type's interface; they can think abstractly about what the type does rather than concretely about how the type works.

Encapsulation is a term that describes the technique of combining lower-level elements to forma new, higher-level entity. A function is one form of encapsulation: The detailed actions performedby the function are encapsulated in the larger entity that is the function itself. Encapsulated elements hide the details of their implementationwe may call

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安徽工业大学毕业设计（论文）说明书

a function but have no access to the statements that it executes. In the same way, a class is an encapsulated entity: It represents an aggregation of several members, and most (well-designed) class types hide the members that implement the type.

If we think about the library vector type, it is an example of both data abstraction and encapsulation. It is abstract in that to use it, we think about its interfaceabout the operations that it can perform. It is encapsulated because we have no access to the details of how the type is representated nor to any of its implementation artifacts. An array, on the other hand, is similar in concept to a vector but is neither abstract nor encapsulated. We manipulate an array directly by accessing the memory in which the array is stored.

Not all types need to be abstract. The library pair class is a good example of a useful, well-designed class that is concrete rather than abstract. A concrete class is a class that exposes, rather than hides, its implementation.

Some classes, such as pair, really have no abstract interface. The pair type exists to bundle two data members into a single object. There is no need or advantage to hiding the data members. Hiding the members in a class like pair would only complicate the use of the type.

Even so, such types often have member functions. In particular, it is a good idea for any class that has data members of built-in or compound type to define constructor(s) to initialize those members. The user of the class could initialize or assign to the data members but it is less error-prone for the class to do so.

Programmers tend to think about the people who will run their applications as "users." Applicationsare designed for and evolve in response to feedback from those who ultimately "use" the applications. Classes are thought of in a similar way: A class designer designs and implements a class for "users" of that class. In this case, the "user" is a programmer, not the ultimate user of the application.

Authors of successful applications do a good job of understanding and implementing the needs ofthe application's users. Similarly, well-designed, useful classes are designed with a close attention to the needs of the users of the class.

In another way, the division between class designer and class user reflects the division betweenusers of an application and the designers and implementors of the application. Users care only if the application meets their needs in a cost-effective way. Similarly, users of a class care only about its interface. Good class designers define a class interface that is intuitive and easy to use. Users care about the implementation only in so far as the implementation affects their use of the class. If the implementation is too slow or puts burdens on users of the class, then the users must care. In well-designed classes, only the class designer worries about the implementation.

In simple applications, the user of a class and the designer of the class might be one

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安徽工业大学毕业设计（论文）说明书

and the same person. Even in such cases, it is useful to keep the roles distinct. When designing the interface to a class, the class designer should think about how easy it will be to use the class. When using the class, the designer shouldn't think about how the class works.

When referring to a "user," the context makes it clear which kind of user is meant. If we speak of "user code" or the "user" of the Sales_item class, we mean a programmer who is using a class in writing an application. If we speak of the "user" of the bookstore application, we mean the manager of the store who is running the application.

Data abstraction and encapsulation provide two important advantages:

1.Class internals are protected from inadvertent user-level errors, which might corrupt the state of the object.

2.The class implementation may evolve over time in response to changing requirements or bug reports without requiring change in user-level code.

By defining data members only in the private section of the class, the class author is free to make changes in the data. If the implementation changes, only the class code needs to be examined to see what affect the change may have. If data are public, then any function that directly accesses the data members of the old representation might be broken. It would be necessary to locate and rewrite all those portions of code that relied on the old pesentation before the program could be used again.

Similarly, if the internal state of the class is private, then changes to the member data can happen in only a limited number of places. The data is protected from mistakes that users might introduce. If there is a bug that corrupts the object's state, the places to look for the bug are localized: When data are private, only a member function could be responsible for the error. The search for the mistake is limited, greatly easing the problems of maintenance and program correctness.

If the data are private and if the interface to the member functions does not change, then user functions that manipulate class objects require no change.

Because changing a class definition in a header file effectively changes the text of every source file that includes that header, code that uses a class must be recompiled when the class changes.

Classes are the most fundamental feature in C++. Classes let us define new types that are tailored to our own applications, making our programs shorter and easier to modify.Data abstractionthe ability to define both data and function membersand encapsulationthe ability to protect class members from general accessare fundamental to classes. Member functions define the interface to the class. We encapsulate the class by making the data and functions used by the implementation of a class private.

Classes may define constructors, which are special member functions that control how

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安徽工业大学毕业设计（论文）说明书

objects of the class are initialized. Constructors may be verloaded. Every constructor should initialize every data member. Constructors should use a constructor initializer list to initialize the data members. Initializer lists are lists of namevalue pairs where the name is a member and the value is an initial value for that member.

Classes may grant access to their nonpublic members to other classes or functions. A class grants access by making the class or function a friend.

Classes may also define mutable or static members. A mutable member is a data member that is never const; its value may be changed inside a const member function. A static member can be either function or data; static members exist independently of the objects of the class type.

Copy Control

Each type, whether a built-in or class type, defines the meaning of a (possibly empty) set of operations on objects of that type. We can add two int values, run size on a vector, and so on. These operations define what can be done with objects of the given type.

Each type also defines what happens when objects of the type are created. Initialization of objects of class type is defined by constructors. Types also control what happens when objects of the type are copied, assigned, or destroyed. Classes control these actions through special member functions: the copy constructor, the assignment operator, and the destructor. This chapter covers these operations.

When we define a new type, we specifyexplicitly or implicitlywhat happens when objects of that type are copied, assigned, and destroyed. We do so by defining special members: the copy constructor, the assignment operator, and the destructor. If we do not explicitly define the copy constructor or the assignment operator, the compiler will (usually) define them for us.

The copy constructor is a special constructor that has a single parameter that is a (usually const) reference to the class type. The copy constructor is used explicitly when we define a new object and initialize it from an object of the same type. It is used implicitly when we pass or return objects of that type to or from functions.

Collectively, the copy constructor, assignment operator, and destructor are referred to as copy control. The compiler automatically implements these operations, but the class may define its own versions.

Copy control is an essential part of defining any C++ class. Programmers new to C++ are often confused by having to define what happens when objects are

copied, assigned, or destroyed. This confusion is compounded because if we do not explicitly define these operations, the compiler defines them for usalthough they might not behave as we intend.

Often the compiler-synthesized copy-control functions are finethey do exactly the

篇三：毕业设计的5000字英文文献翻译

外文及翻译

英语原文 Android Application Fundamentals

Android applications are written in the Java programming language. The Android SDK tools compile the code—along with any data and resource files—into an Android package, an archive file with an .apk suffix. All the code in a single .apk file is considered to be one application and is the file that Android-powered devices use to install the application. Once installed on a device, each Android application lives in its own security sandbox: ? The Android operating system is a multi-user Linux system in which each

application is a different user.

? By default, the system assigns each application a unique Linux user ID (the ID is used only by the system and is unknown to the application). The system sets

permissions for all the files in an application so that only the user ID assigned to that application can access them.

? Each process has its own virtual machine (VM), so an application's code runs in isolation from other applications.

? By default, every application runs in its own Linux process. Android starts the process when any of the application's components need to be executed, then shuts down the process when it's no longer needed or when the system must recover

memory for other applications.

However, there are ways for an application to share data with other applications and for an application to access system services:

? It's possible to arrange for two applications to share the same Linux user ID, in which

case they are able to access each other's files. To conserve system resources,

applications with the same user ID can also arrange to run in the same Linux process

and share the same VM (the applications must also be signed with the same

certificate).

? An application can request permission to access device data such as the user's

contacts, SMS messages, the mountable storage (SD card), camera, Bluetooth, and

more. All application permissions must be granted by the user at install time.

That covers the basics regarding how an Android application exists within the system. The rest of this document introduces you to: ? The core framework components that define your application.

? The manifest file in which you declare components and required device features for

your application.

? Resources that are separate from the application code and allow your application to

gracefully optimize its behavior for a variety of device configurations.

Application Components

There are four different types of application components. Each type serves a distinct purpose and has a distinct lifecycle that defines how the component is created and destroyed.

Here are the four types of application components:

Activities

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activities (if the email application allows it). For example, a camera application can start the activity in the email application that composes new mail, in order for the user to share a picture.

An activity is implemented as a subclass of Activity and you can learn more about it in the Activities developer guide.

Services

A service is implemented as a subclass of Service and you can learn more about it in the Services developer guide. Content providers

Content providers are also useful for reading and writing data that is private to your application and not shared. For example, the Note Pad sample application uses a content provider to save notes.

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Broadcast receivers

A broadcast receiver is a component that responds to system-wide broadcast announcements. Many broadcasts originate from the system—for example, a broadcast announcing that the screen has turned off, the battery is low, or a picture was captured. Applications can also initiate broadcasts—for example, to let other applications know that some data has been downloaded to the device and is available for them to use. Although broadcast receivers don't display a user interface, they may create a status bar notification to alert the user when a broadcast event occurs. More commonly, though, a broadcast receiver is just a "gateway" to other components and is intended to do a very minimal amount of work. For instance, it might initiate a service to perform some work based on the event.

A broadcast receiver is implemented as a subclass of BroadcastReceiver and each broadcast is delivered as an Intent object. For more information, see theBroadcastReceiver class.

Therefore, unlike applications on most other systems, Android applications don't have a single entry point (there's no main() function, for example).

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another application, you must deliver a message to the system that specifies your intent to start a particular component. The system then activates the component for you.

Activating Components

Three of the four component types—activities, services, and broadcast receivers—are activated by an asynchronous message called an intent. Intents bind individual components to each other at runtime (you can think of them as the messengers that request an action from other components), whether the component belongs to your application or another.

An intent is created with an Intent object, which defines a message to activate either a specific component or a specific type of component—an intent can be either explicit or implicit, respectively.

For activities and services, an intent defines the action to perform (for example, to "view" or "send" something) and may specify the URI of the data to act on (among other things that the component being started might need to know). For example, an intent might convey a request for an activity to show an image or to open a web page. In some cases, you can start an activity to receive a result, in which case, the activity also returns the result in

an Intent (for example, you can issue an intent to let the user pick a personal contact and have it returned to you—the return intent includes a URI pointing to the chosen contact).

For broadcast receivers, the intent simply defines the announcement being broadcast (for example, a broadcast to indicate the device battery is low includes only a known action string that indicates "battery is low").

The other component type, content provider, is not activated by intents. Rather, it is

activated when targeted by a request from a ContentResolver. The content resolver handles all direct transactions with the content provider so that the component that's performing

transactions with the provider doesn't need to and instead calls methods on

the ContentResolver object. This leaves a layer of abstraction between the content provider and the component requesting information (for security).

There are separate methods for activating each type of component:

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