Java Exam 6.5

It is a best practice to use explicit import ◦to properly (1) which Java API class is being used in your program. ◦to avoid (2) errors because of possible (3) for classes with the (4) name. ◦to assist in looking for one specific file versus (5) for all (6) during compilation. ◦to avoid (7) performance issues with (8) field and method processing when using JSP (JavaServer Pages) to create web pages with dynamic content.

1.document 2.compilation 3.name collisions 4.same 5.searching 6.matches 7.runtime 8.static

A _______ ________with the same name as a ________hides or _______ the class-level variable.

1.parameter 2.variable 3.field 4. shadows

Using ____ in a field declaration____ ____ _____.

1.public 2.compromises 3.code 4.security

Classes that are compiled in the same directory are considered to be in the _____ package—known as the default package.

1.same

An import declaration is not required 1.when one class in a package uses another in the _____ package. 2.if you always refer to a class with its fully qualified _____, which includes its package name and ________ ________.

1.same 2.class name, class name

Classes in the default package are implicitly _____ into the source-code files of other classes in that package.

2.imported

package.

A group of associated Java classes organized in a folder

What are methods of a class?

A grouping of code −representing a set of tasks −to perform a particular purpose. §Code that is divided for efficiency: input, processing, output. Allows other programs to use a class's code through objects.

wildcard import statement

Another way to import [multiple classes from the same package]1 is to use a wildcard import statement. A wildcard import statement tells the compiler to import all of the classes in a package. Here is an example: import java.util.*;

client/server relationship.

Any Java class can create an object of another Java class to use that other class's code.

default package

Classes in the same directory reside in a default package, and they don't have to be imported.

determines whether a Java class needs to be imported for use in another Java class.

Packaging

Object-Oriented Design: Problem Domain

Set of real-world objects, parties, and major events [processes]1 related to the problem. Need to fully understand the nature of the problem.

wildcard statement *

The .* that follows the package name tells the compiler to import all the classes that are part of the java.util package.

The java.lang Package

The Java API does have one package, java.lang, which is automatically imported into every Java program. This package contains general classes, such as String and System, that are fundamental to the Java programming language [because they are often used by other Java programs]1.

the default package.

There's a special relationship between classes that are compiled in the same directory. By default, such classes are considered to be in the same package—known as the default package

If an instance field is declared with the public access specifier, it can also be accessed by code outside the class, as long as an instance of the class exists.

This is dangerous and compromises code security.1

does the wildcard statement mess things up?

Using a wildcard import statement does not affect the performance [during runtime]2 or the size of your program. It merely tells the compiler that you want to make every class in a particular package available to your program. Still better to use explicit tho

Scope of Instance Fields

Variables declared as instance fields in a class can be accessed by any instance method in the same class as the field.

An application class

a Java class that has a main() which kick starts the processing by creating an object of the stand-alone class and uses that object to call the necessary methods from the stand-alone class.

Server classes

are imported if they reside in another directory; otherwise, they are defaulted to the same package or directory as the client class if they reside in the same directory. Therefore, no import statement is required.

Many of the classes in the Java API are/are not automatically available to your program.

are not

The tasks performed in a program is

contextual.

There are two types of import statements

explicit and wildcard.

Classes have

fields, class-level variables, to store the data that comes into the program.The data comes in and goes out through methods that process the data.

Methods are _______ of code representing a _________ of ________ for a particular __________ .

groupings; b. set; c. tasks; d. purpose .

An explicit import statement

identifies the package location of a single class. •For example, the following statement explicitly identifies the location of the Scanner class: import java.util.Scanner;

The classes in the Java API are organized into packages. An _____ statement tells the compiler the package in which a class is located.

import

Write an explicit import statement for the Calendar class that is in the java.util package.

import java.util.Calendar;

The Java API

is a standard library of prewritten classes. Each class in the Java API is designed for a specific purpose, and you can use the classes in your own programs.

A package

is like a folder. Classes in the same package are implicitly imported into the source-code files of other classes in that package.

The java.util package is/is not automatically imported for all Java programs.

is not

A package

is simply a group of related classes. Each package also has a name. For example, the Scanner class is in the java.util package.

A few of the standard Java API packages

java.io Provides classes that perform various types of input and output. java.lang Provides general classes for the Java language. This package is automatically imported. java.net Provides classes for network communications. java.security Provides classes that implement security features. java.sql Provides classes for accessing databases using structured query language. java.text Provides various classes for formatting text. java.util Provides various utility classes. javax.swing Provides classes for creating graphical user interfaces.

Which package requires no import statement?

java.lang

What Java package is needed to use the JOptionPane class?

javax.swing

Standard Java API.

library of classes that serve programmers in building their own Java programs,

The Java API is a standard _________ of ________ classes.

library; prewritten

In OOD, __________ help to identify potential _______ that will process things that they ________ by what they are suppose to _________.

nouns; b. classes; c. know; d. do

An _______ of a ________ class is _________ in a _________ class to facilitate code reuse.

object; b. server; c. instantiated; d. client

A Java class is a ____ with and ________ ________.

program; fields; methods

import statement

tells the compiler which package a class is located in.

A Java stand-alone class is created how?

the same way as any other class except it does not have a main(). Its class variables are usually not static and is declared using the access specifier private. It'll have a constructor and its method headers are usually not static.

Classes are imported if they reside in another directory; otherwise,

they are defaulted to the same package, which requires no import statement.

Finding the Classes

ºGet [a]1 written description of the problem domain. ºIdentify all nouns, each is a potential class. §What are the actors inside and outside of a computerized system that have to interact with that system?2 Refine list to include only classes relevant to the problem.

Identify the Responsibilities

ºThings a class is responsible for knowing [data to be stored]3. ºThings a class is responsible for doing [how the data is to be processed]4. ºRefine list to include only classes relevant to the problem.

Description of problem domain includes

ºphysical objects, ºroles played by people, ºresults of a business event [or process]2 ºrecordkeeping items.

Shadowing

•A parameter variable is, in effect, a local variable. •Within a method, variable names must be unique. •A method may have a local variable with the same name as an instance field. •This is called shadowing. •The local variable will hide the value of the instance field. •Shadowing is discouraged ... [so]1 local variable names should ... be [different than]2 ... instance field names.

objects

−An object of a class is created using a constructor. −The object is given a name called a reference variable. −The reference variable points to the object. −The object is used to call the class's methods (code).

feilds

◦Collectively, fields describe an object and the methods the object's behavior (what it can do).

What is a class?

◦It is a Java program. ◦It contains fields to store data. ◦It contains methods to process data and perform other functions.

An import declaration

◦is not required when one class in a package uses another in the same package. ◦is not required if you always refer to a class with its fully qualified class name, which includes its package name and class name.

It is a best practice to use explicit import why?

◦to properly document which Java API class is being used in your program. ◦to avoid compilation errors because of possible name collisions for classes with the same name. §Naming conflicts cause hard-to-find compile errors: wildcard can't differentiate between Event from java.awt.Event or Event from an organization's calendar system - com.mycompany.calendar.Event.1 ◦to assist in looking for one specific file versus searching for all matches during compilation. ◦to avoid runtime performance issues with static field and method processing when using JSP (JavaServer Pages) to create web pages with dynamic content. ◦to, although miniscule, minimize compile time. ◦to minimize exposing your program to any unnecessary classes.