Java Reference

CIS 277 - Washtenaw Community College

Late update: 01/16/2002

TOC

  1. Primitive data types
  2. Java operators
  3. Java tools in the SDK
  4. Java classes in the JDK (partial list)
  5. Contents of the java.lang class
  6. General Java program skeleton

Primitive data types

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These are the primitive data types for Java.

Type Contains Default Size Min Value Max Value
boolean true or false false 1 bit N/A N/A
char Unicode character /u0000 16 bits /u0000 /uFFFF
byte signed integer 0 8 bits -128 127
short signed integer 0 16 bits -32768 32767
int signed integer 0 32 bits -2147483648 2147483647
long signed integer 0 64 bits -9223372036854775808 -9223372036854775807
float IEEE 754 floating-point 32 bits 0.0 1.40239846E-45 3.40282347E+38
double IEEE754 floating-point 0.0 64 bits 4.94065645841246544E-324 1.79769313486231570E+308

Java operators

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Basic operators for the language.

Operator Operand type(s) Performs
++ arithmetic pre- or post- increment
-- arithmetic pre- or post- decrement
+, - arithmetic plus, minus
~ integral bitwise complement
! boolean logical complement
( type ) any cast
*, /, % arithmetic multiply, divide, remainder
+, - arithmetic addition, subtraction
+ string concatenation
<< integral left shift
>> integral right shift
>>> integral right shift with zero extension
<, <= arithmetic less than, less than or equal
>, >= arithmetic greater than, greater than or equal
instanceof object, type type comparison
== primitive equals (have identical values)
!= primitive not equal (have different values)
== object refers to the same object
!= object does not refer to the same object
& integral bitwise AND
& boolean boolean AND
^ integral bitwise XOR
^ boolean boolean XOR
| integral bitsize OR
&& boolean conditional AND
|| boolean conditional OR
? : boolean, any, any conditional operator
= variable, any assignment 
+=, /=, 
%=, *=, 
-=, <<=, 
>>=, >>>=, 
&=, ^=, |=
variable, any assignment with operations

Java tools in the SDK

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This list contains the various command line tools you use for the various Java related programming functions.

Each of these commands has a variety of parameters you can enter to modify the behavior of the command.

Full documentation is available in the Java Documentation in the section titled "Tool Documentation".

Command Description
java runs a program contained in a class file
javac compiles a .java file into a .class file
appletviewer used for testing applets
javadoc generate source code documentation
jar command used to build jar files
javap dis-assemble a Java program to source code
jdb Java debugger

Java classes in the JDK (partial list)

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When you install the Java language, you are giving yourself access to dozens of class libraries to use code that has already been written.

The documentation for each of these classes contains a list of the methods and properties of the method, as well as reference to the class's superclasses and all of its inherited methods and properties.

Some of the packages are listed below. For a complete list, look at the Java Documentation in the section titled "Java 2 Platform API Specification".

Class Contents
java.applet Provides the classes necessary to create an applet and the classes an applet uses to communicate with its applet context.
java.awt Contains all of the classes for creating user interfaces and for painting graphics and images.
java.beans Contains classes related to Java Beans development.
java.io Provides for system input and output through data streams, serialization and the file system.
java.lang Provides classes that are fundamental to the design of the Java programming language.
java.math Provides classes for performing arbitrary-precision integer arithmetic (BigInteger) and arbitrary-precision decimal arithmetic (BigDecimal).
java.net Provides the classes for implementing networking applications.
java.sql Provides the API for accessing and processing data in a data source using the JavaTM programming language.
java.text Provides classes and interfaces for handling text, dates, numbers, and messages in a manner independent of natural languages.
java.util Contains the collections framework, legacy collection classes, event model, date and time facilities, internationalization, and miscellaneous utility classes (a string tokenizer, a random-number generator, and a bit array).
javax.swing Provides a set of "lightweight" (all-Java language) components that, to the maximum degree possible, work the same on all platforms.
org.omg.CORBA Provides the mapping of the OMG CORBA APIs to the JavaTM programming language, including the class ORB, which is implemented so that a programmer can use it as a fully-functional Object Request Broker (ORB).

Contents of the java.lang class

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The java.lang package contains all of the basic data objects we will use for writing programs.

The table below contains a list of the objects in java.lang and a short description of each.

Class Description
Boolean The Boolean class wraps a value of the primitive type boolean in an object.
Byte The Byte class is the standard wrapper for byte values.
Character The Character class wraps a value of the primitive type char in an object.
Character.Subset Instances of this class represent particular subsets of the Unicode character set.
Character.UnicodeBlock A family of character subsets representing the character blocks defined by the Unicode 2.0 specification.
Class Instances of the class Class represent classes and interfaces in a running Java application.
ClassLoader The class ClassLoader is an abstract class.
Compiler The Compiler class is provided to support Java-to-native-code compilers and related services.
Double The Double class wraps a value of the primitive type double in an object.
Float The Float class wraps a value of primitive type float in an object.
InheritableThreadLocal This class extends ThreadLocal to provide inheritance of values from parent Thread to child Thread: when a child thread is created, the child receives initial values for all InheritableThreadLocals for which the parent has values.
Integer The Integer class wraps a value of the primitive type int in an object.
Long The Long class wraps a value of the primitive type long in an object.
Math The class Math contains methods for performing basic numeric operations such as the elementary exponential, logarithm, square root, and trigonometric functions.
Number The abstract class Number is the superclass of classes Byte, Double, Float, Integer, Long, and Short.
Object Class Object is the root of the class hierarchy.
Package Package objects contain version information about the implementation and specification of a Java package.
Process The Runtime.exec methods create a native process and return an instance of a subclass of Process that can be used to control the process and obtain information about it.
Runtime Every Java application has a single instance of class Runtime that allows the application to interface with the environment in which the application is running.
RuntimePermission This class is for runtime permissions.
SecurityManager The security manager is a class that allows applications to implement a security policy.
Short The Short class is the standard wrapper for short values.
StrictMath The class StrictMath contains methods for performing basic numeric operations such as the elementary exponential, logarithm, square root, and trigonometric functions.
String The String class represents character strings.
StringBuffer A string buffer implements a mutable sequence of characters.
System The System class contains several useful class fields and methods.
Thread A thread is a thread of execution in a program.
ThreadGroup A thread group represents a set of threads.
ThreadLocal This class provides ThreadLocal variables.
Throwable The Throwable class is the superclass of all errors and exceptions in the Java language.
Void The Void class is an uninstantiable placeholder class to hold a reference to the Class object representing the primitive Java type void.

General Java program skeleton

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The following shows a general skeleton for a Java program. 

// package declaration (optional)
package sample;

// import other classes (optional)
import java.awt.*;
import java.lang.*;

// class definition
[public] [abstract|final] class SampleOne 
	[extends JFrame] [implements Runnable] {
	
// class variables, instance variables, constants
[public|private|protected] [final] [static] [primtype] 
	varOne [= value];
[public|private|protected] [final] [static] [primtype] 
	varTwo [= new String();];
[public|private|protected] [final] [static] [primtype] 
	varThree [= new String("abc");];

// class method definitions?

static {
	...code...
	}
	
	// constructors for the current class
	[public|private|protected] SampleOne(parameters)
	{
		...code...
	}
	
	// class and instance methods
	[public|private|protected] [synchronized] 
	[abstract|final|static|native] 
	[return type] myFirstMethod(parameters)
		{
		...code...
		return valOrVoid;
		}
}