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© 1999, Pinnacle Software Solutions Inc. © 1999, Pinnacle Software Solutions Inc.
Java Programming Guide - Quick Reference
© 1999, Pinnacle Software Solutions Inc.
Java Programming Guide - Quick Reference
© 1999, Pinnacle Software Solutions Inc.
Syntax for a standalone application in Java:
class { public static void main(String args[]) { statements; ————————; ————————; } }
Steps to run the above application:
- Type the program in the DOS editor or notepad. Save the file with a .java extension.
- The file name should be the same as the class, which has the main method.
- To compile the program, using javac compiler, type the following on the command line: Syntax: javac <filename.java> Example: javac abc.java
- After compilation, run the program using the Java interpreter. Syntax: java (without the .java extension) Example: java abc
- The program output will be displayed on the command line.
Java reserved words:
abstract default if package this boolean do implements private throw Break double import protected throws Byte else instanceof public transient case extends int return null try Const for new switch continue while goto synchronized super Catch final interface short void char finally long static volatile class float native
Java naming conventions:
Variable Names: Can start with a letter, ‘$’ (dollar symbol), or ‘_’ (underscore); cannot start with a number; cannot be a reserved word.
Method Names: Verbs or verb phrases with first letter in lowercase, and the first letter of subsequent words capitalized; cannot be reserved words. Example: setColor()
Class And Interface Names: Descriptive names that begin with a capital letter, by convention; cannot be a reserved word.
Constant Names: They are in capitals. Example: Font.BOLD, Font.ITALIC
Java Comments:
Delimiters Use // Used for commenting a single line
/* ————— */ Used for commenting a block of code
/** —————*/ Used for commenting a block of code. Used by the Javadoc tool for generating Java documentation.
Primitive datatypes in Java:
DataType Size Default Min Value Max Value byte (Signed - integer) 8 bits 0 +
short (Signed -32, integer) 16 bits 0 +32,
int (Signed -2,147,483, integer) 32 bits 0 +2,147,483,
long -9, 223, 372,036,854, (Signed 775,808, Integer) +9,223,372,036, 64 bits 0 854, 775, 807
float 32 bits 0.0 1.4E- (IEEE 754 3.4028235E floating-point)
double 64 bits 0.0 4.9E- (IEEE 754 1.7976931348623157E floating-point)
char 16 bits \u0000 \u (Unicode character) \uFFFF boolean 1 bit false
Variable Declaration: Example: int num1;
Variable Initialization: = value Example: double num2 = 3.1419;
Escape sequences: Literal Represents \n New line \t Horizontal tab \b Backspace \r Carriage return
© 1999, Pinnacle Software Solutions Inc. © 1999, Pinnacle Software Solutions Inc.
Java Programming Guide - Quick Reference
© 1999, Pinnacle Software Solutions Inc.
Java Programming Guide - Quick Reference
© 1999, Pinnacle Software Solutions Inc.
\f Form feed \ Backslash \” Double quote \ddd Octal character \xdd Hexadecimal character \udddd Unicode character
Arrays: An array which can be of any datatype, is created in two steps – array declaration and memory allocation.
Array declaration [] <arr ```````````ayname>; Examples int[] myarray1; double[] myarray2; Memory Allocation The new keyword allocates memory for an array. Syntax = new []; Examples myarray1 = new int[10]; Myarray2 = new double[15];
Multi-dimensional arrays:
Syntax: [] [] = new [number of rows][number of columns]; Example: int mdarray[][] = new int[4][5];
Flow Control:
- If……..else statements Syntax: if(condition) { statements; } else { statements; }
- For loop Syntax: for(initialization; condition; increment) { statements; }
- While loop Syntax: while(condition) { statements; }
- Do….While loop Syntax: do { statements; } while(condition);
- Switch statement Syntax: switch(variable) { case(value1): statements; break; case(value2): statements; break; default: statements; break; }
Class Declaration: A class must be declared using the keyword class followed by the class name. Syntax class { ———— Body of the class
A typical class declaration is as follows: class extends implements { —————Member variable declarations; —————Method declarations and definitions }
Member variable declarations:
<static/final/transient/ volatile> Example public final int num1;
Method declarations:
<static/final> { Method body; } Example public static void main(String args[]) { }
Interface declaration: Create an interface. Save the file with a.java extension, and with the same name as the interface. Interface methods do not have any implementation and are abstract by default.
Syntax interface { void abc(); void xyz(); }
Using an interface: A class implements an interface with the implements keyword.
© 1999, Pinnacle Software Solutions Inc. © 1999, Pinnacle Software Solutions Inc.
Java Programming Guide - Quick Reference
© 1999, Pinnacle Software Solutions Inc.
Java Programming Guide - Quick Reference
© 1999, Pinnacle Software Solutions Inc.
NullPointerException Invalid use of a null reference.
NumberFormatException Invalid conversion of a string to a number.
SecurityException Thrown when security is violated.
ClassNotFound Thrown when a class is not found. Exception
CloneNotSupported Attempt to clone an object that Exception does not implement the Cloneable interface.
IllegalAccess Thrown when a method does not Exception have access to a class.
Instantiation Thrown when an attempt is made Exception to instantiate an abstract class or an interface.
InterruptedException Thrown when a second thread interrupts a waiting, sleeping, or paused thread.
The java.lang.Thread class
The Thread class creates individual threads. To create a thread either (i) extend the Thread class or (ii) implement the Runnable interface. In both cases, the run() method defines operations
performed by the thread.
Methods of the Thread class:
Methods Description
run() Must be overridden by Runnable object; contains code that the thread should perform start() Causes the run method to execute and start the thread
sleep() Causes the currently executing thread to wait for a specified time before allowing other threads to execute
interrupt() Interrupts the current thread
Yield() Yields the CPU to other runnable threads
getName() Returns the current thread’s name
getPriority() Returns the thread’s priority as an integer
isAlive() Tests if the thread is alive; returns a Boolean value
join() Waits for specified number of milliseconds for a thread to die
setName() Changes the name of the thread
setPriority() Changes the priority of the thread
currentThread() Returns a reference to the currently executing thread
activeCount() Returns the number of active threads in a thread group
Exception Handling Syntax:
try { //code to be tried for errors } catch(ExceptionType1 obj1) { //Exception handler for ExceptionType } catch(ExceptionType2 obj2) { //Exception handler for ExceptionType } finally{ //code to be executed before try block ends. This executes whether or not an // exception occurs in the try block. }
I/O classes in Java (part of the java.io package):
I/O class name Description
BufferedInputStream Provides the ability to buffer the
input. Supports mark() and reset() methods. BufferedOutputStream Provides the ability to write bytes to the underlying output stream without making a call to the underlying system.
BufferedReader Reads text from a character input stream BufferedWriter Writes text to character output stream DataInputStream Allows an application to read primitive datatypes from an underlying input stream DataOutputStream Allows an application to write primitive datatypes to an output stream File Represents disk files and directories FileInputStream Reads bytes from a file in a file system FileOutputStream Writes bytes to a file ObjectInputStream Reads bytes i.e. deserializes objects using the readObject() method ObjectOutputStream Writes bytes i.e. serializes objects using the writeObject()method PrintStream Provides the ability to print different data values in an efficient manner RandomAccessFile Supports reading and writing to a random access file
© 1999, Pinnacle Software Solutions Inc. © 1999, Pinnacle Software Solutions Inc.
Java Programming Guide - Quick Reference
© 1999, Pinnacle Software Solutions Inc.
Java Programming Guide - Quick Reference
© 1999, Pinnacle Software Solutions Inc.
StringReader Character stream that reads from a string
StringWriter Character stream that writes to a StringBuffer that is later converted to a String
The java.io.InputStream class: The InputStream class is at the top of the input stream hierarchy. This is an abstract class which cannot be instantiated. Hence, subclasses like the DataInputStream class are used for input purposes.
Methods of the InputStream class:
Method Description available() Returns the number of bytes that can be read
close() Closes the input stream and releases associated system resources
mark() Marks the current position in the input stream mark Supported() Returns true if mark() and reset() methods are supported by the input stream
read() Abstract method which reads the next byte of data from the input stream
read(byte b[]) Reads bytes from the input stream and stores them in the buffer array
skip() Skips a specified number of bytes from the input stream
The java.io.OutputStream class: The OutputStream class which is at the top of the output stream hierarchy, is also an abstract class, which cannot be instantiated. Hence, subclasses like DataOutputStream and PrintStream are used for output purposes.
Methods of the OutputStream class:
Method Description
close() Closes the output stream, and releases associated system resources
write(int b) Writes a byte to the output stream
write(byte b[]) Writes bytes from the byte array to the output stream
flush() Flushes the ouput stream, and writes buffered output bytes
java.io.File class: The File class abstracts information about files and directories.
Methods of the File class:
Method Description
exists() Checks whether a specified file exists
getName() Returns the name of the file and directory denoted by the path name isDirectory() Tests whether the file represented by the pathname is a directory lastModified() Returns the time when the file was last modified l length() Returns the length of the file represented by the pathname listFiles() Returns an array of files in the directory represented by the pathname setReadOnly() Marks the file or directory so that only read operations can be performed renameTo() Renames the file represented by the pathname delete() Deletes the file or directory represented by the pathname canRead() Checks whether the application can read from the specified file canWrite() Checks whether an application can write to a specified file
Creating applets:
- Write the source code and save it with a .java extension
- Compile the program
- Create an HTML file and embed the .class file with the
- To execute the applet, open the HTML file in the browser or use the appletviewer utility, whch is part of the Java Development Kit.
The
Using the Appletviewer: Appletviewer.exe is an application found in the BIN folder as part of the JDK. Once an HTML file containing the class file is created (eg. abc.html), type in the command line: Appletviewer abc.html
java.applet.Applet class:
Methods of the java.applet.Applet class:
Method Description
init() Invoked by the browser or the applet viewer to inform that the applet has been loaded start() Invoked by the browser or the applet viewer to inform that applet execution has started stop() Invoked by the browser or the applet viewer to inform that applet execution has stopped
© 1999, Pinnacle Software Solutions Inc. © 1999, Pinnacle Software Solutions Inc.
Java Programming Guide - Quick Reference
© 1999, Pinnacle Software Solutions Inc.
Java Programming Guide - Quick Reference
© 1999, Pinnacle Software Solutions Inc.
Methods of the Button class:
Method Description addActionListener() Registers an ActionListener object to receive action events from the button
getActionCommand() Returns the command name of the action event fired by the button. Returns the button label if the command name is null.
GetLabel() Returns the button’s label
SetLabel() Sets the button’s label to the specified string
Checkbox:
Constructors
· Checkbox() - Creates a checkbox without any label · Checkbox(String s) - Creates a checkbox with a specified label · Checkbox(String s, boolean state) - Creates a checkbox with a specified label, and sets the specified state · Checkbox(String s, boolean state, CheckboxGroup cbg) - Creates a checkbox with a specified label and specified state, belonging to a specified checkbox group
Methods of the Checkbox class:
Method Description
addItemListener() Registers an ItemListener object to receive item events from the checkbox
getCheckboxGroup() Returns the checkbox’s group
getLabel() Returns the checkbox’s label
getState() Determines if the checkbox is checked or unchecked
setLabel() Sets the label of the check box with the specified string
setState() Sets the specified checkbox state
Creating Radio Buttons (Mutually exclusive checkboxes):
· First create a CheckboxGroup instance – CheckboxGroup cbg = new CheckboxGroup(); · While creating the checkboxes, pass the checkbox group object as an argument to the constructor - Checkbox (String s, boolean state, CheckboxGroup cbg)
Choice:
Constructors
Choice() - Creates a new choice menu, and presents a pop- up menu of choices.
Methods of the Choice class:
Method Description
add() Adds an item to a choice menu
addItem() Adds an item to a choice menu
addItemListener() Registers an ItemListener object to receive item events from the Choice object
getItem() Returns the item at the specified index as a string
getItemCount() Returns the number of items in the choice menu
getSelectedIndex() Returns the index number of the currently selected item
getSelectedItem() Returns the currently selected item as a string
insert() Inserts a specified item at a specified index position
remove() Removes an item from the choice menu at the specified index
TextField:
Constructors
· TextField() - Creates a new text field · TextField(int cols) - Creates a text field with the specified number of columns · TextField(String s) – Creates a text field initialized with a specified string · TextField(String s, int cols) - Creates a text field initialized with a specified string that is wide enough to hold a specified number of columns
Methods of the TextField class:
Method Description
isEditable() Returns a boolean value indicating whether or not a text field is editable
setEditable() Passing True enables text to be edited, while False disables editing. The default is True.
addActionListener() Registers an ActionListener object to receive action events from a text field
getEchoChar() Returns the character used for echoing
getColumns() Returns the number of columns in a text field
© 1999, Pinnacle Software Solutions Inc. © 1999, Pinnacle Software Solutions Inc.
Java Programming Guide - Quick Reference
© 1999, Pinnacle Software Solutions Inc.
Java Programming Guide - Quick Reference
© 1999, Pinnacle Software Solutions Inc.
setEchoChar() Sets the echo character for a text field getText() Returns the text contained in the text field setText() Sets the text for a text field
TextArea:
Constructors
· TextArea() - Creates a new text area · TextArea(int rows, int cols) - Creates a new empty text area with specified rows and columns · TextArea(String s) – Creates a new text area with the specified string · TextArea(String s, int rows, int cols) - Creates a new text area with the specified string and specified rows and columns. · TextArea(String s, int rows, int cols, int scrollbars) - Creates a text area with the specified text, and rows, columns, and scrollbar visibility as specified.
Methods of the TextArea class:
Method Description
getText() Returns the text contained in the text area as a string
setText() Sets the specified text in the text area
getRows() Returns the number of rows in the
text area getColumns() Returns the number of columns in the text area
selectAll() Selects all the text in the text area
setEditable() A True value passed as an argument enables editing of the text area, while False disables editing. It is True by default.
List:
Constructors
· List() - Creates a new scrolling list · List(int rows) - Creates a new scrolling list with a specified number of visible lines · List(int rows, boolean multiple) - Creates a scrolling list to display a specified number of rows. A True value for Multiple allows multiple selection, while a False value allows only one item to be selected.
Methods of the List class:
Method Description
add() Adds an item to the end of the scrolling list
addItemListener() Registers an ItemListener object to receive Item events from a scrolling list
deselect() Deselects the item at the specified index position
getItem() Returns the item at the specified index position
getItemCount() Returns the number of items in the list
getSelectedIndex() Returns the index position of the selected item
getSelectedItem() Returns the selected item on the scrolling list
isMultipleMode() Determines if the scrolling list allows multiple selection
remove() Removes a list item from a specified position
setMultipleMode() Sets a flag to enable or disable multiple selection
Scrollbar:
Constructors
· Scrollbar() - Creates a new vertical scroll bar · Scrollbar(int orientation) - Creates a new scroll bar with a particular orientation, which is specified as Scrollbar.HORIZONTAL or Scrollbar.VERTICAL · Scrollbar(int orientation, int value, int visible, int minimum, int maximum)- Creates a new scroll bar with the specified orientation, initial value, thumb size, minimum and maximum values
Methods of the Scrollbar class:
Method Description
addAdjustmentListener() Registers an adjustmentListener object to receive adjustment events from a scroll bar getBlockIncrement() Returns the block increment of a scrollbar as an integer. getMaximum() Returns the maximum value of a scrollbar as an integer getMinimum() Returns the minimum value of a scrollbar as an integer getOrientation() Returns the orientation of a scrollbar as an integer getValue() Returns the current value of a scrollbar as an integer
© 1999, Pinnacle Software Solutions Inc. © 1999, Pinnacle Software Solutions Inc.
Java Programming Guide - Quick Reference
© 1999, Pinnacle Software Solutions Inc.
Java Programming Guide - Quick Reference
© 1999, Pinnacle Software Solutions Inc.
keyTyped() Invoked whenever a key is typed
MouseListener interface: Implemented by a class handling mouse events. It comprises of five methods invoked when a MouseEvent object is generated. Its corresponding adapter class is the MouseAdapter class.
Method Description
mouseClicked() Invoked when mouse is clicked on a component
mouseEntered() Invoked when mouse enters a component
mouseExited() Invoked when mouse exits a component
mousePressed() Invoked when mouse button is pressed on a component
mouseReleased() Invoked when mouse button is released on a component
MouseMotionListener interface: Implemented by a class for receiving mouse-motion events. Consists of two methods – mouseDragged() and mouseMoved(), which is invoked when a MouseEvent object is generated. MouseMotionAdapter is its corresponding adapter class.
Method Description
mouseDragged() Invoked when the mouse is pressed on a component and dragged
mouseMoved() Invoked when mouse is moved over a component
WindowListener interface: Implemented by a class to receive window events. It consists of seven different methods to handle the different kinds of window events, which are invoked when a WindowEvent object is generated. Its corresponding adapter class is the WindowAdapter class.
Method Description
windowOpened() Invoked when the window is made visible for the first time
windowClosing() Invoked when the user attempts to close the window from the Windows system menu
windowClosed() Invoked when the window has been closed as a result of calling the dispose() method
windowActivated() Invoked when the window is made active i.e. the window can receive keyboard events
windowDeactivated() Invoked when the window is no longer the active window i.e. the window can no longer receive keyboard events
windowIconified() Invoked when a normal window is minimized
windowDeiconified() Invoked when a minimized window is changed to normal state
java.sql.Driver interface: Implemented by every driver class.
Methods of the Driver interface:
Method Description
acceptsURL() Returns a Boolean value indicating whether the driver can open a connection to the specified URL
connect() Tries to make a database connection to the specified URL
getMajorVersion() Returns the driver’s major version number
getMinorVersion() Returns the driver’s minor version number
jdbcCompliant() Tests whether the driver is a genuine JDBC compliant driver
java.sql.Connection interface: Represents a session with a specific database. SQL statements are executed within a session and the results are returned.
Methods of the Connection interface:
Method Description
Close() Immediately releases the database and JDBC resources
commit() Makes all changes since the last commit/rollback permanent, and releases the database locks held by the connection
createStatement() Creates and returns a Statement object. It is used for sending SQL statements to be executed on the database
getMetaData() Returns a DatabaseMetaData object that represents metadata about the database
isReadOnly() Checks whether the connection is a read-only connection
prepareCall() Creates and returns a Callable Statement object,
© 1999, Pinnacle Software Solutions Inc. © 1999, Pinnacle Software Solutions Inc.
Java Programming Guide - Quick Reference
© 1999, Pinnacle Software Solutions Inc.
Java Programming Guide - Quick Reference
© 1999, Pinnacle Software Solutions Inc.
prepareCall() Creates and returns a CallableStatement object (used for calling database stored procedures) prepareStatement() Creates and returns a PreparedStatement object (used for sending precompiled SQL statements to the database) rollback() Discards all the changes made since the last commit/rollback and releases database locks held by the connection setAutoCommit() Enables or disables the auto commit feature. It is disabled by default
java.sql.DriverManager class: Responsible for managing a set of JDBC drivers. It attempts to locate and load the JDBC driver specified by the getConnection() method.
Methods of the DriverManager class:
Method Description
getConnection() Attempts to establish a database connection with the specified database URL, and returns a Connection object
getLoginTimeout() Returns the maximum number of seconds a driver can wait when attempting to connect to the database
registerDriver() Registers the specified driver with the DriverManager
setLoginTimeout() Sets the maximum number of seconds a driver can wait when attempting to connect to the database
getDrivers() Returns an enumeration of all the drivers installed on the system
getDriver() Returns a Driver object that supports connection through a specified URL
