Summary of Example Classes

Summary of Example Classes from Day1 and Day2

The descriptions in this document are models of class descriptions for the users of the class. However, most of these descriptions are abbreviated, listing only the instance variables and methods that are actually used in the Day1 and Day2 examples. For a complete description of a class, see the Keyboard Class Description.

Class System

Instance Variables

public static PrintStream err
The standard error object.
public static PrintStream in
The standard input object.
public static PrintStream out
The standard output object. We have used the methods print and println from this object.

Methods

public static void gc()
Runs the garbage collector, which reclaims the memory in objects whose reference count is zero.

See the description of the System class on Page 744 of Lewis and Loftus of other methods. They perform system tasks like configuring security managers, getting system time, loading libraries, etc.

Class Coin

Constructor

public Coin()
Creates a Coin object with side chosen randomly.

Methods

public void flip()
Sets the value of side randomly.
public String toString()
Returns a string indicating which face is showing ("head" or "tail").

Class JOptionPane

import javax.swing.JOptionPane;

Static Methods

public static String showInputDialog()
Show an input box.
public static void showMessageDialog()
Show a message box. The return value is the string that the user enters.

Class String

Constructor

public String(String str)
Creates a String object from the String parameter str. Usually, str is expressed as a constant string in double quotes.

Methods

public int length()
Returns the length of the string.
public char charAt(int pos)
Returns the character at the position pos, where the position is zero-based.

For more methods, see page 739 of Lewis and Loftus.

Class Integer

The class Integer is an example of a wrapper class. We may or may not cover wrapper classes later in this course. What interests us now are its static instance variables.

Static Instance Variables

public final static int MAX_VALUE
The largest posible int value 2147483647.
public final static int MIN_VALUE
The largest posible int value -2147483648.

The classes Byte, Boolean, Char, Float, Long, and Short are also available. Each of these classes contains MAX_VALUE and MIN_VALUE instance variables. See the descriptions of these classes in Appendix M of Lewis and Loftus for more details, including methods.

Class Keyboard

import cs1.Keyboard;

IMPORTANT: To use the Keyboard class, get the disk that came with Lewis and Loftus and copy the copy the cs1.jar file from the Keyboard folder on the CD drive to the folder \jdk1.3\jre\lib\ext on your computer. Here is cs1.jar if you prefer to download it from here.

The Keyboard class inputs characters from the keyboard, and interprets it as whitespace delimited pieces of data. Whitespace consists of the characters ' ', '\t', '\r', '\n', '\f'.

Static Methods

public static int readInt()
Read and return an integer from the keyboard. If the input cannot be interpreted as an integer, Integer.MIN_VALUE is returned.
Similar methods readString, readWord, readChar, readBoolean, readLong, readFloat, readDouble are also available. See The Keyboard Class for more details.
public static boolean getPrintErrors()
Returns true if errors due to illegal input are being printed to the screen, false otherwise.
public static void setPrintErrors(boolean state)
Determines whether error messages due to illegal input are printed to the screen.

Class Math

The Example Math in Day2 should be self explanatory.

Class DecimalFormat

Constructor

public DecimalFormat(String formatString)
Creates a DecimalFormat object containing the specified formatString.

Methods

public String format(int formatString)
public String format(double formatString)
Returns a string representing the formatted value of the input int or double. See Page 662 of Lewis and Loftus for a discussion of more DecimalFormat methods.

Class Applet

Although we will postpone a detailed discussion of inheritance until after the midterm exam, for now if a class B inherits a class A, the class B has all the functionality of A with the extra functionality provided in B. We say that B is a derived class with the base class A. If B ® A means that B is derived from A, the Applet class has the following inheritance hierarchy:
Applet® Panel ® Container ® Component ® Object.

Constructor

public Applet()
Creates a new applet for inclusion on a web page or to view in the applet viewer.

Methods

public void paint(Graphics g)
Paint text or graphics on the applet using the graphics context g. The paint method is actually inherited from the Container class, but can be used as a normal Applet method.

Class Color

Static Color Constants

public final static Color black
public final static Color blue
public final static Color green
public final static Color red
etc....

See Lewis and Loftus on Page 646 for more color constants.

Constructors

public Color(float r, float g, float b)
public Color(int r, int g, int b)

See Lewis and Loftus on Page 646 for more Color methods.

Class Graphics

Methods

public Color getBackground()
public void setBackground(Color c)
Get of set the background color.
public Color getColor()
public void setColor(Color c)
Get of set the drawing or fill color.
public void fillOval(int x, int y, int width, int height)
Draw a filled rectangle with upper left corner at position (x,y) and with the given width and height.
Other useful methods for the Applet Project are drawLine, drawString, drawRect, fillRect, drawRoundRect, fillRoundRect, drawOval, drawArc, drawPolygon, fillPolygon, getFont, setFont. See the other applet examples in Section 3.10 of Lewis and Loftus, and the description of the Applet class in Appendix M on Page 681.