Home > Articles > Programming > Java

  • Print
  • + Share This
This chapter is from the book

20.6 The Data Byte Streams

Reading and writing text characters is useful, but you also frequently need to transmit the binary data of specific types across a stream. The DataInput and DataOutput interfaces define methods that transmit primitive types across a stream. The classes DataInputStream and DataOutputStream provide a default implementation for each interface. We cover the interfaces first, followed by their implementations.

20.6.1 DataInput and DataOutput

The interfaces for data input and output streams are almost mirror images. The parallel read and write methods for each type are

Read

Write

Type

readBoolean

writeBoolean

boolean

readChar

writeChar

char

readByte

writeByte

byte

readShort

writeShort

short

readInt

writeInt

int

readLong

writeLong

long

readFloat

writeFloat

float

readDouble

writeDouble

double

readUTF

writeUTF

String (in UTF format)

String values are read and written using a modified form of the UTF-8 character encoding. This differs from standard UTF-8 in three ways: the null byte (\u0000) is encoded in a 2-byte format so that the encoded string does not have embedded null bytes; only 1-byte, 2-byte, or 3-byte formats are used; and supplementary characters are encoded using surrogate pairs. Encoding Unicode characters into bytes is necessary in many situations because of the continuing transition from 8-bit to 16-bit character sets.

In addition to these paired methods, DataInput has several methods of its own, some of which are similar to those of InputStream:

  • public abstract void readFully(byte[] buf, int offset, int count) throws IOException
    • Reads into part of a byte array. The maximum number of bytes read is count. The bytes are stored from buf[offset] up to a maximum of buf[offset+count-1]. If count is zero then no bytes are read. This method blocks until input is available, the end of the file (that is, stream) is found—in which case an EOFException is thrown—or an exception is thrown because of an I/O error.
  • public abstract void readFully(byte[] buf) throws IOException
    • Equivalent to readFully(buf,0, buf.length).
  • public abstract int skipBytes(int count) throws IOException
    • Attempts to skip over count bytes, discarding any bytes skipped over. Returns the actual number of bytes skipped. This method never throws an EOFException.
  • public abstract int readUnsignedByte() throws IOException
    • Reads one input byte, zero-extends it to type int, and returns the result, which is therefore in the range 0 through 255. This method is suitable for reading a byte written by the writeByte method of DataOutput if the argument to writeByte was a value in the range 0 through 255.
  • public abstract int readUnsignedShort() throws IOException
    • Reads two input bytes and returns an int value in the range 0 through 65535. The first byte read is made the high byte. This method is suitable for reading bytes written by the writeShort method of DataOutput if the argument to writeShort was a value in the range 0 through 65535.

The DataInput interface methods usually handle end-of-file (stream) by throwing EOFException when it occurs. EOFException extends IOException.

The DataOutput interface supports signatures equivalent to the three forms of write in OutputStream and with the same specified behavior. Additionally, it provides the following unmirrored methods:

  • public abstract void writeBytes(String s) throws IOException
    • Writes a String as a sequence of bytes. The upper byte in each character is lost, so unless you are willing to lose data, use this method only for strings that contain characters between \u0000 and \u00ff.
  • public abstract void writeChars(String s) throws IOException
    • Writes a String as a sequence of char. Each character is written as two bytes with the high byte written first.

There are no readBytes or readChars methods to read the same number of characters written by a writeBytes or writeChars invocation, therefore you must use a loop on readByte or readChar to read strings written with these methods. To do that you need a way to determine the length of the string, perhaps by writing the length of the string first, or by using an end-of-sequence character to mark its end. You could use readFully to read a full array of bytes if you wrote the length first, but that won't work for writeChars because you want char values, not byte values.

20.6.2 The Data Stream Classes

For each Data interface there is a corresponding Data stream. In addition, the RandomAccessFile class implements both the input and output Data interfaces (see Section 20.7.2 on page 541). Each Data class is an extension of its corresponding Filter class, so you can use Data streams to filter other streams. Each Data class has constructors that take another appropriate input or output stream. For example, you can use the filtering to write data to a file by putting a DataOutputStream in front of a FileOutputStream object. You can then read the data by putting a DataInputStream in front of a FileInputStream object:

public static void writeData(double[] data, String file)
    throws IOException
{
    OutputStream fout = new FileOutputStream(file);
    DataOutputStream out = new DataOutputStream(fout);
    out.writeInt(data.length);
    for (double d : data)
        out.writeDouble(d);
    out.close();
}

public static double[] readData(String file)
    throws IOException
{
    InputStream fin = new FileInputStream(file);
    DataInputStream in = new DataInputStream(fin);
    double[] data = new double[in.readInt()];
    for (int i = 0; i < data.length; i++)
        data[i] = in.readDouble();
    in.close();
    return data;
}

The writeData method first opens the file and writes the array length. It then loops, writing the contents of the array. The file can be read into an array with readData. These methods can be rewritten more simply using the Object streams you will learn about in Section 20.8 on page 549.

Exercise 20.7 : Add a method to the Attr class of Chapter 3 that writes the contents of an object to a DataOutputStream and add a constructor that will read the state from a DataInputStream.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020