Lesson 4.1: Advanced Programming Logic

Question 1

What is an I/O stream?

Answer 1

An I/O stream is an abstraction that either produces or consumes information. A stream is linked to a physical device by the Java I/O system. All streams behave in the same manner، even if the actual physical devices they are linked to differ.

Question 2

What two types of streams do modern versions of Java define?

Answer 2

Modern versions of Java define two types of I/O streams: byte and character. (The original version of Java defined only the byte stream، but character streams were quickly added.)

Question 3

When are byte streams used over character streams?

Answer 3

Byte streams provide a convenient means for handling input and output of bytes. They are used، for example، when reading or writing binary data. They are especially helpful when working with files.

Question 4

When are character streams used over byte streams?

Answer 4

Character streams are designed for handling the input and output of characters. They use Unicode and، therefore، can be internationalized. Also، in some cases، character streams are more efficient than byte streams.

Question 5

At the most basic level، which stream is the only stream used? Why do we still use the other if we only (ultimatley) use both?

Answer 5

At the lowest level، all I/O is still byte-oriented. The character-based streams simply provide a convenient and efficient means for handling characters.

Question 6

What do InputStream and OutputStream define?

Answer 6

InputStream defines the characteristics common to byte input streams and OutputStream describes the behavior of byte output streams.

Question 7

What are the byte stream classes by name. Since there are so many، here is a hint: BI،BO،AI،AO،DS،DO،FI،FO،LI،LO، etc. Dont expect to memorize them

Answer 7

The byte stream classes in java.io are shown in Table 10-1. Don’t be overwhelmed by the number of different classes. Once you can use one byte stream، the others are easy to master.

Question 8

What are the two class hierarchy abstract classes that character streams are topped by?

Answer 8

Character streams are defined by using two class hierarchies topped by these two abstract classes: Reader and Writer.

Question 9

Which one is which for input and output: reader and writer

Answer 9

Reader is used for input، and Writer is used for output. Concrete classes derived from Reader and Writer operate on Unicode character streams.

Question 10

What are the several concrete subclasses that are derived from Reader and Writer?

Answer 10

From Reader and Writer are derived several concrete subclasses that handle various I/O situations. In general، the character-based classes parallel the byte-based classes. The character stream classes in java.io are shown in Table 10-2.

Question 11

By default، what do System.out، System.in، and System.err refer to?

Answer 11

System.out refers to the standard output stream. By default، this is the console. System.in refers to standard input، which is by default the keyboard. System.err refers to the standard error stream، which is also the console by default. However، these streams can be redirected to any compatible I/O device.

Question 12

What system commands are Input stream and which are output stream?

Answer 12

System.in is an object of type InputStream; System.out and System.err are objects of type PrintStream.

Question 13

Name 3 (out of the many) InputStream methods and 3 OutputStream methods.

Answer 13

At the top of the byte stream hierarchy are the InputStream and OutputStream classes. Table 10-3 shows the methods in InputStream، and Table 10-4 shows the methods in OutputStream.

Question 14

For commercial coding، what is the preferred stream orientation? Why

Answer 14

For commercial code، the preferred method of reading console input is to use a character-oriented stream. Doing so makes your program easier to internationalize and easier to maintain.

Question 15

What are the three different versions of read()

Answer 15

There are three versions of read( )، which are shown here: int read( ) throws IOException int read(byte data[ ]) throws IOException int read(byte data[ ]، int start، int max) throws IOException

Question 16

What does int read( ) throws IOException do?

Answer 16

In Chapter 3، you saw how to use the first version of read( ) to read a single character from the keyboard (from System.in). It returns –1 when an attempt is made to read at the end of the stream.

Question 17

What does int read(byte data[ ]) throws IOException do?

Answer 17

The second version reads bytes from the input stream and puts them into data until either the array is full، the end of stream is reached، or an error occurs. It returns the number of bytes read، or –1 when an attempt is made to read at the end of the stream.

Question 18

What does int read(byte data[ ]، int start، int max) throws IOException do?

Answer 18

The third version reads input into data beginning at the location specified by start. Up to max bytes are stored. It returns the number of bytes read، or –1 when an attempt is made to read at the end of the stream.

Question 19

print() and println() are methods of what class stream?

Answer 19

Console output is most easily accomplished with print( ) and println( )، with which you are already familiar. These methods are defined by the class PrintStream (which is the type of the object referenced by System.out).

Question 20

What is the simplest form of write()?

Answer 20

it is possible to write to the console by using write( ). The simplest form of write( ) defined by PrintStream is shown here: void write(int byteval) This method writes the byte specified by byteval to the file. Although byteval is declared as an integer، only the low-order 8 bits are written.

Question 21

What are some of the methods in the abstract classes Reader and Writer?

Answer 21

At the top of the character stream hierarchy are the abstract classes Reader and Writer. Table 10-7 shows the methods in Reader، and Table 10-8 shows the methods in Writer. Most of the methods can throw an IOException on error.

Question 22

What is the best class for reading console input and when can you use it directly with System.in?

Answer 22

The best class for reading console input is BufferedReader، which supports a buffered input stream. However، you cannot construct a BufferedReader directly from System.in. Instead، you must first convert it into a character stream. To do this، you will use InputStreamReader، which converts bytes to characters. To obtain an InputStreamReader object that is linked to System.in، use the constructor shown next: InputStreamReader(InputStream inputStream) Next، using the object produced by InputStreamReader، construct a BufferedReader using the constructor shown here: BufferedReader(Reader inputReader) Putting it all together، the following line of code creates a BufferedReader that is connected to the keyboard.

Question 23

What does int read( ) throws IOException int read(char data[ ]) throws IOException int read(char data[ ]، int start، int max) throws IOException do?

Answer 23

int read( ) throws IOException int read(char data[ ]) throws IOException int read(char data[ ]، int start، int max) throws IOException The first version of read( ) reads a single Unicode character. It returns –1 when an attempt is made to read at the end of the stream. The second version reads characters from the input stream and puts them into data until either the array is full، the end of stream is reached، or an error occurs. It returns the number of characters read or –1 when an attempt is made to read at the end of the stream. The third version reads input into data beginning at the location specified by start. Up to max characters are stored. It returns the number of characters read or –1 when an attempt is made to read at the end of the stream.

Question 24

What is the general form of readLine()?

Answer 24

To read a string from the keyboard، use the version of readLine( ) that is a member of the BufferedReader class. Its general form is shown here: String readLine( ) throws IOException

Question 25

Give me a code example that uses BufferedReader and the readLine() method.

Answer 25

The following program demonstrates BufferedReader and the readLine( ) method. The program reads and displays lines of text until you enter the word “stop”.

Question 26

Why is it preferred to use PrintWriter over System.out in large scale programs?

Answer 26

using a character-based class for console output makes it easier to internationalize your program.

Question 27

What are two commonly used FileWriter constructors?

Answer 27

FileWriter creates a Writer that you can use to write to a file. Two commonly used constructors are shown here: FileWriter(String fileName) throws IOException FileWriter(String fileName، boolean append) throws IOException Here، fileName is the full path name of a file. If append is true، then output is appended to the end of the file. Otherwise، the file is overwritten. Either throws an IOException on failure. FileWriter is derived from OutputStreamWriter and Writer. Thus، it has access to the methods defined by these classes.

Question 28

Give me a code that uses key to disk utility and writes lines of text to a txt file.

Answer 28

Here is a simple key-to-disk utility that reads lines of text entered at the keyboard and writes them to a file called "test.txt". Text is read until the user enters the word "stop". It uses a FileWriter to output to the file.

Question 29

What does a FileReader class do? What is a commonly used constructor for a FileReader?

Answer 29

The FileReader class creates a Reader that you can use to read the contents of a file. A commonly used constructor is shown here: FileReader(String fileName) throws FileNotFoundException Here، fileName is the full path name of a file. It throws a FileNotFoundException if the file does not exist.

Question 30

Write a code that reads a text file using simple disk-to-screen utility.

Answer 30

The following program creates a simple disk-to-screen utility that reads a text file called "test.txt" and displays its contents on the screen. Thus، it is the complement of the key-to-disk utility shown in the previous section.

Question 31

What is NIO

Answer 31

Originally called New I/O، NIO was added to Java by JDK 1.4. It supports a channel-based approach to I/O operations. The NIO classes are contained in java.nio and its subordinate packages، such as java.nio.channels and java.nio.charset.

Question 32

What is NIO.2?

Answer 32

Beginning with JDK 7، NIO was substantially enhanced، so much so that the term NIO.2 is often used. The improvements included three new packages (java.nio.file، java.nio.file.attribute، and java.nio.file.spi); several new classes، interfaces، and methods; and direct support for stream-based I/O. The additions greatly expanded the ways in which NIO can be used، especially with files.

Question 33

Why are type wrappers needed?

Answer 33

Java’s type wrappers are classes that encapsulate، or wrap، the primitive types. Type wrappers are needed because the primitive types are not objects.

Question 34

What are the type wrappers?

Answer 34

The type wrappers are Double، Float، Long، Integer، Short، Byte، Character، and Boolean. These classes offer a wide array of methods that allow you to fully integrate the primitive types into Java’s object hierarchy. As a side benefit، the numeric wrappers also define methods that convert a numeric string into its corresponding binary equivalent.

Question 35

Try This 10-1: A File Comparison Utility

Answer 35

*Try This 10-1 A File Comparison Utility*

Question 36

Try This 10-2: Creating a Disk-Based Help System

Answer 36

*Try This 10-2 Creating a Disk-Based Help System*