1 CS1001 Lecture 13. 2 Overview Java Programming Java Programming.
Windows Programming Using Java
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Transcript of Windows Programming Using Java
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I N S T R U C T O R : S H I H - S H I N H H UA N G
Windows Programming Using Java
Chapter2: Introduction to Java Applications
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Contents
IntroductionA First Program in JavaText DisplayingValue Input: Integer AdditionArithmeticEquality and Relational Operators
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Introduction
Java Keywordsabstract do import public throws
boolean double instanceof return transient
break else int short trybyte extends interface static voidcase final long strictfp volatilecatch finally native super whilechar float new switch
class for package synchronized
continue if private this
default implements protected throw
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Introduction
Identifier Rule Series of characters consisting of letters,
digits, underscores ( _ ) and dollar signs ( $ )
“Welcome1”, “$value”, “_value”, “button7” are valid
“7button” is invalid Case sensitive (capitalization matters)
a1 and A1 are different
Identifier = (letter | '_' | ' $ ') {letter | digit | '_'}.
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Introduction
Primitive Data TypeData Type Purpose Contents Default Value*boolean Truth value true or false faleschar Character Unicode characters \u0000
byte Signed integer 8 bit two's complement (byte) 0
short Signed integer 16 bit two's complement (short) 0
int Signed integer 32 bit two's complement 0
long Signed integer 64 bit two's complement 0L
float Real number 32 bit IEEE 754 floating point 0.0f
double Real number 64 bit IEEE 754 floating point 0.0d
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A First Program in Java
Function: printing a line of text 1 // Fig. 2.1: Welcome1.java 2 // Text-printing program. 3 4 public class Welcome1 { 5 6 // main method begins execution of Java application 7 public static void main( String args[] ) 8 { 9 System.out.println( "Welcome to Java Programming!" ); 10 11 } // end method main 12 13 } // end class Welcome1
Welcome to Java Programming!
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A First Program in Java
Comments // remainder of line is comment
Comments ignored Document and describe code
Multiple line comments: /* ... */
1 // Fig. 2.1: Welcome1.java
/* This is a multiple line comment. It can be split over many lines */
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A First Program in Java
Class Declaration
Every Java program has at least one defined class
Keyword: words reserved for use by Javaclass keyword followed by class nameThe class name has to be an identifier
Naming Convention: capitalize every word Example: SampleClassName
4 public class Welcome1 {
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A First Program in Java
Body Delimiter Left brace {
Begins body of every class A corresponding right brace “}” ends definition
(line 13)
Indentation Convention Whenever you type an left brace “{“, immediately
type the right brace “}”. Then, indent to begin type the body.
4 public class Welcome1 {
13}/* End of Class Welcome1 */
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A First Program in Java
Program Entry Applications begin executing at main()
Exactly one method must be called main Parenthesis indicate main is a method Java applications contain one or more methods
Methods can perform tasks and return result void: means main returns no information args[]:input arguments in String data type.
5 public static void main( String args[] )
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A First Program in Java
Statements Statements are instructions to commend
hardware to perform some operations. It must end with semicolon “;”
System.out: standard output object System.out.println: displays line of text
7 System.out.println("Welcome to Java Programming!" );
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A First Program in Java
Execution Steps
Javacompiler
Javasource code byte-code
EXECUTION
JAVA PROGRAM EXECUTION
byte-codeinterpreter
JVM
Welcome.java
.class
javac Welcome.java
java Welcome
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A First Program in Java
Execution Steps Compiling a program
Open a command window, go to program’s directory.
Type javac Welcome.java If no errors, Welcome.class created
Executing a program Type java Welcome to start JVM and then run
the program Welcome.class Interpreter calls method main
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A First Program in Java
Demonstration 4 public class Welcome1 { 5 6 // main method begins execution of Java application 7 public static void main( String args[] ) 8 { 9 System.out.println( "Welcome to Java Programming!" ); 10 11 } // end method main 12 13 } // end class Welcome1
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Text Displaying
Displaying MethodsSystem.out.println
Prints argument, puts cursor on new lineSystem.out.print
Prints argument, keeps cursor on same lineSystem.out.printf
Prints argument which is a format string
7 System.out.println("Welcome to Java Programming!" );
7 System.out.print("Welcome to “);8 System.out.println(“Java Programming!" );
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Text Displaying
Escape Sequences The backslash “\” is called an escape
character to indicate a “special character” is to be output.
Backslash combined with character makes escape sequence.Escape Sequence Description
\n Newline\t Horizontal Tab\r Carriage Return. Position the cursor at the
beginning of the current line\\ Backslash\” Double Quote
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Text Displaying
Escape Sequences7 System.out.println("Welcome\nto\nJava\n
Programming!" );
WelcometoJavaProgramming!
7 System.out.println(“\”in quotes\”" );
“in quotes”
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Text Displaying
Format String The first argument of printf() is a format
string Fixed Text Format Specifier
Format specifier is a placeholder for a value and specifies the type of data. Percent Sign (“%”) Data Type
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Text Displaying
Format StringType Character
Input String Result
%c char character%d signed int signed decimal integer%f float real number, standard notation%s string string
7 System.out.printf(“%s\n%s\n”, “Welcome to”, “Java Programming!" );
Welcome toJava Programming!
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Value Input: Integer Addition
Requirements Read in two integers from users Compute the summation of them Print out the result on the screen
Enter first integer:1Enter second integer:3Sum is: 4
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Value Input: Integer Addition
Variable Declaration Every variable has a name, a type, a size and a value
Name corresponds to location in memory When new value is placed into a variable, replaces
(and destroys) previous value Reading them from memory does not change them
int number1=10;
int number1;number1=10;
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Value Input: Integer Addition
Variable Declarationpublic class Addition {
// main method begins execution of Java applicationpublic static void main( String args[] ){
int number1;int number2;int sum;…………
}/* End of main */
}/* End of class Addition */
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Value Input: Integer Addition
import java.util.Scanner;public class Addition {
// main method begins execution of Java applicationpublic static void main( String args[] ){
……// create Scanner to obtain input from command windowScanner input = new Scanner( System.in );// read the first integer System.out.print("Enter first integer:");number1 = input.nextInt();// read the second integerSystem.out.print("Enter second integer:");number2 = input.nextInt();……
}/* End of main */}/* End of class Addition */
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Value Input: Integer Addition
import java.util.Scanner;public class Addition {
// main method begins execution of Java applicationpublic static void main( String args[] ){
……sum = number1 + number2;System.out.printf("Sum is: %d\n", sum);}/* End of main */}/* End of class Addition */
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Arithmetic
Description Arithmetic calculations used in most
programs Asterisk ‘*’ indicates multiplication Percent sign ‘%’ is the remainder (modulus)
operator Integer division truncates remainder7 / 5 evaluates to 1
Modulus operator % returns the remainder 7 % 5 evaluates to 2
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Arithmetic
Operator precedence Some arithmetic operators act before
othersOperator(s) Operation(s) Order of evaluation (precedence)
() Parentheses Evaluated first. If the parentheses are nested, the expression in the innermost pair is evaluated first. If there are several pairs of parentheses “on the same level” (i.e., not nested), they are evaluated left to right.
*, /, or % Multiplication Division Modulus
Evaluated second. If there are several, they are evaluated left to right.
+ or - Addition Subtraction
Evaluated last. If there are several, they are evaluated left to right.
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Equality and Relational Operators
Description A condition is an expression that can be
either true or false. It is used in control statements (if, for,
while) to change the execution flow of program
Conditions can be formed by using Equality Operators Relational Operators
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Equality and Relational Operators
Equality/Relational OperatorsStandard Algebraic
Java Equality
Sample Meaning
= == x == y x is equal to y?!= x != y x is not equal to y ?
> > x > y x is greater than y ?< < x < y x is less than y?
>= x >= y x is greater than or equal to y
<= x <= y x is less than or equal to y
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Equality and Relational Operators
Exampleimport java.util.Scanner;public class Comparison {
public static void main( String args[] ){int number1=100;int number2=200;if(number1 == number2){System.out.printf(“%d == %d \n”, number1, number2);}/* End of if-condition */if(number1 != number2){System.out.printf(“%d != %d \n”, number1, number2);}/* End of if-condition */
}/* End of main */}/* End of class Addition */
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