Example Java Programs

General Information

Some Common, Simple Tasks

How to get some simple chores done: random numbers, date formatting, properties, string tokenizer, stream tokenizer, and enumeration types.

Random Numbers

Flip.java

      final Random coin = new Random();
      final int flip_result = coin.nextInt(2);

Date Formatting

(We looked at number formatting earlier.) An internationalized resource bundling using the Java class and class.

The class uses special pattern characters to refer to the components of a date or time text.

Symbol	Meaning	Presentation Kind	Example
`G`	era designator	Text	`AD`
`y`	year	Year	`yyy:96 yyyy:1996`
`M`	month in year	Month	`M:7 MM:07 MMM:Jul MMMM:July`
`w`	week in year	Number	`27`
`W`	week in month	Number	`2`
`D`	day in year	Number	`189`
`d`	day in month	Number	`10`
`F`	day of week in month; as in: 2nd Tue in Jul	Number	`2`
`E`	day in week	Abbreviated Text	`EEE:Tue EEEE:Tuesday`
`a`	am/pm marker	Text	`PM`
`H`	hour in day (0-23)	Number	`13`
`k`	hour in day (1-24)	Number	`24`
`K`	hour in am/pm (0-11)	Number	`0`
`h`	hour in am/pm (1-12)	Number	`11`
`m`	minute in hour	Number	`m:3 mm:03 mmm:003`
`s`	second in minute	Number	`55`
`S`	millisecond	Number	`978`
`z`	time zone	Abbreviated Text	`zzz:EST zzzz:Eastern Standard Time`
`Z`	time zone (RFC 822)	Text	`-0800`

Number. The number of pattern letters is the minimum number of digits, and shorter numbers are zero-padded to this amount.
Month, Year. The style of these formats are special to their respective data types.

Properties

Hello.java
List.java Output showing a list of all system properties.

Property Name	description
`file.encoding`	The character encoding for the default locale
`file.encoding.pkg`	The package that contains the converters that handle converting between local encodings and Unicode
`java.awt.fonts`
`java.awt.graphicsenv`
`java.awt.printerjob`
`java.class.path`	The value of the CLASSPATH environment variable
`java.class.version`	The version of the Java API
`java.compiler`	The just-in-time compiler to use, if any. Initialized from the environment variable JAVA_COMPILER.
`java.ext.dirs`	The directory in which Java extentions are installed
`java.home`	The directory in which Java is installed
`java.io.tmpdir`	The directory in which Java should create temporary files
`java.security.policy`
`java.version`	The version of the Java interpreter
`java.vendor`	A vendor-specific string
`java.vendor.url`	A vendor URL
`java.vm.info`
`java.vm.name`
`java.vm.specification.name`
`java.vm.specification.vendor`
`java.vm.specification.version`
`java.vm.vendor`
`java.vm.version`
`file.separator`	The platform-dependent file separator (e.g., "/" on UNIX, "\" for Windows)
`path.separator`	The platform-dependent path separator (e.g., ":" on UNIX, "," for Windows)
`line.separator`	The platform-dependent line separator (e.g., "\n" on UNIX, "\r\n" for Windows)
`os.arch`	The system architecture
`os.name`	The name of the operating system
`os.version`	The operating system version
`user.dir`	The current working directory when the properties were initialized
`user.home`	The home directory of the current user
`user.language`	The two-letter language code of the default locale Solaris: initialized from env var LANG
`user.name`	The username of the current user
`user.region`	The two-letter country code of the default locale
`user.timezone`	The default time zone
`font.properties`	Java 1.2 AWT
`swing.defaultlaf`	Control look-and-feel
`awt.image.incrementaldraw`	if true (default) draw parts of images as it arrives.
`awt.image.redrawrate`	Minimum period in milliseconds between calls to repraint (default is 100)

property	Unix	Windows	MacIntosh
`file.separator`	`/`	`\`	`:`
`line.separator`	`\n`	`\r\n`	`\r`
`path.separator`	`:`	`;`	`:`

readln reads all three types of lines on all three types of systems. println writes the kind of line appropriate for the system. line+line.separator File(String) recognizes only the file separator for the system it is being run on.

Property File Format

A description of the file format for property files can be found in the documentation for the method of the class

String Tokenizer

The following are examples using the Java class. They are often used with (see examples elsewhere). The Java class is often used while reading the input as in the Read.java program.

Add.java
Parse.java
URL.java
Table.java
See also Iter.java that uses java.util.Iterator and inner classes.

Stream Tokenizer

Examples using the Java class.

NumberStream.java (Sum a stream of numbers --- not a fixed number of numbers on the line.)
TokenizerText.java

A stream tokenizer is initialized to the following default state:

All character values 'A' through 'Z', 'a' through 'z', and '\u00A0' through '\u00FF' are considered to be alphabetic.
All character values '\u0000' through '\u0020' are considered to be white space.
'/' is a comment character.
Single quote '\'' and double quote '"' are string quote characters.
Numbers are parsed.
Ends of lines are treated as white space, not as separate tokens.
C-style and C++-style comments are not recognized.

Unless the syntax table is reset, the StreamTokenizer methods add new ranges of characters to the individual categories and does not replace the initial ranges.

Regular Expressions

Using method

GroupMain.java

Enumeration Types

No enumeration type like C++'s

      enum color { red, orange, yellow, green, blue };

Suit.java

Ryan Stansifer <ryan@cs.fit.edu>

Last modified: Tue Nov 4 16:24:06 EST 2003