Download Java Notes: Chapter 2 First Java Programs

Java Notes: Chapter 2
First Java Programs
Secure:
Robust:
Portable:
Encapsulation – Enables objects to hide their implementation from other objects – a principle called
information hiding. Preventing outside classes from changing field variables.
Implies the idea of DO ONE THING AND DO IT WELL!!
Instance Method:
Static Method:
Library:
BASIC OUTLINE OF A JAVA APPLICATION:
//Purpose: To convert a Fahrenheit temperature to Celcius
// Name: Mrs. Spurgeon
// Date: Nov. 1, 2007
import java.util.Scanner;
public class TempConverter
{
public static void main (String [] args)
{ int fahrenheit;
double celcius;
System.out.println ("Temperature Converter");
Scanner reader = new Scanner (System.in);
System.out.print ("Enter a fahrenheit temperature: ");
fahrenheit= reader.nextInt();
celcius = (fahrenheit - 32.0) * 5.0/9.0;
System.out.println ("The equivalent temperature in Celcius is " +celcius);
}
}
Options to using an existing library or class:
1.
Import the entire library:
____________________________
2.
Import just the classes you need:
____________________________
Website for Java API Documentation: http://java.sun.com/j2se/1.5.0/docs/api/
Displaying output:
System.out.print (“Programming ”);
System.out.println(“is”);
System.out.println (“ cool\n” + “Have fun!”);
Primitive Type:
EIGHT primitive types in Java
Type
Size
String Method Summary:
Range
import java.lang.String
char charAt (int index)
int compareTo(String s2)
boolean equals (Object anObject)
int indexOf(char ch)
String substring (int begIndex)
String substring (int beginIndex, int endIndex)
Comparing two strings:
s1.equals(s2)
NOTE: Do not use == to compare strings!
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EasyReader and EasyFormat classes: (from www.skylit.com\javamethods)
To open the standard input stream for reading keyboard input use
EasyReader reader = new EasyReader();
reader
is the name you give to the input stream (can be anything you like).
Examples for reading data from the keyboard:
int n
= console.readInt();
// reads an integer
double x = console.readDouble(); // reads a double
Note:
readInt, readDouble, readChar,
and readWord methods do not consume the end of the
line after reading the last item. Call readLine to get rid of the tail of the line (even if
only the newline character is left) before calling readLine on the next line.
Working with EasyFormat
The EasyFormat class has static methods for placing items of different types into a string of a
given "width" (length) and right-justified.
Example:
System.out.println("["
System.out.println("["
System.out.println("["
System.out.println("["
System.out.println("["
System.out.println("["
Output:
+
+
+
+
+
+
EasyFormat.format('A', 5)
EasyFormat.format("ABCDEF", 5)
EasyFormat.format(567, 5)
EasyFormat.format(-567, 5)
EasyFormat.format(56.789, 5, 1)
EasyFormat.format(-56.789, 5, 1)
+
+
+
+
+
+
"]");
"]");
"]");
"]");
"]");
"]");
//
//
//
//
//
//
[
A]
[ABCDEF]
[ 567]
[ -567]
[ 56.8]
[-56.8]
Example program to write:
Write a program that asks a user for a location and a number of feet. Calculate
and print the equivalent number of miles, yards and inches.
Graphics and GUIs: Windows and Panels
Standalone GUI applications run in windows.
– Containers for graphical components to be displayed to the user
Windows have numerous properties.
– Width and height
– Title bar
– Ability to be dragged or resized by the user
By default, JFrame uses the border layout
//creating an empty frame
import javax.swing.*; //used to create a JFrame
public class GUIWindow {
public static void main (String[] args) {
} //end of main
} //end of GUIWindow
Some commonly used JFrame methods