Introduction to Java Programming and
ApplicationsCompiler/InterpreterJava languageJava Platforms, JRE
and JDKFirst programs: Hello world, and AdditionSyntax: Things to
remember Other experiencesMemory conceptsPrimitive Data
TypesExpression, Arithmetic and relation operators
XuanTung Hoang*
Interpreter and ComplierComputers need translators to translate
high-level language to machine instructionsInterpreter translates
programs (written in high-level languages) online :Translate and
execute at the same timeStatement by statementCompiler translates
the whole program into machine language before executionTurn
programs text into executable file (in machine language format)When
user wants to run the program, he/she loads the executable file
into computer memory to execute.Portability issue: Different
computer hardwares use different instruction sets (machine
language)We need appropriate interpreter/compiler for each type of
machine
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History of Java languageInitially, Java language is developed
for consumer-electronic devices (embedded systems) (in 1991 by Sun
Microsystems)Also, It turned out to be good for Web and Internet
applicationsAdd dynamic contents (Java applet)Rapid development of
distributed applicationsEase of deployment now Java becomes more
and more attractive for embedded systems (its primary purpose)
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Java PlatformsSun Microsystems provides most of the utilities
for users in Java Platform productsText editorBytecode
compilerClass loaderBytecode Verifier JVM (interpreter)
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Java PlatformsJ2SE: Standard EditionJ2EE: Enterprise
EditionJ2ME: Micro EditionJDK v.s. JRE
+ bytecode compiler+ Class libraries+
+ JVM (interpreter)+ JREJDK
XuanTung Hoang*
Java Development Process5 phasesCreating a program: use text
editor to create program sourceCompiling: use compiler to turn
program source into bytecode (.class files)Loading: use class
loader to load .class files into memoryBytecode verification:
bytecode verifier examines the bytecode for validity and security
concernsExecution: Java Virtual Machine (is a kind of interpreter
for bytecodes) executes the bytecodesCombination of compiling and
interpretingEnhance portability of programs:Write Once Run
AnywhereCompact bytecode files are easy to exchangeBytecode
verifier guarantees securityJust-In-Time compiler enhances
performance
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First Application
Hello.java
1
/* The first program in Java
2
It simply prints out a message */
3
class Hello {
4
public static void main( String[] args ) {
5
// print message
6
System.out.println("Hello world\n");
7
}
8
}
Output:
Hello world
XuanTung Hoang*
First Application: StructureHello.java defines one class: class
HelloKeyword class is used for defining a classClass name follows
keyword classClass body is surrounded by braces { }
Hello.java
1
/* The first program in Java
2
It simply prints out a message */
3
class Hello {
4
public static void main( String[] args ) {
5
// print message
6
System.out.println("Hello world\n");
7
}
8
}
XuanTung Hoang*
First Application: StructureClass body contains methods (or
class functions) and variables:In the example we have only one
method (method main) and no variablesMethod has return type (void)
and parameters ( args )Parameters are given within parenthesis (
)If the method have no parameters, parenthesis are still
requiredModifiers public and static characterize the methodBraces
surrounds method bodymain method is the program entryEvery java
program must have one main function
Hello.java
1
/* The first program in Java
2
It simply prints out a message */
3
class Hello {
4
public static void main( String[] args ) {
5
// print message
6
System.out.println("Hello world\n");
7
}
8
}
XuanTung Hoang*
First Application: StructureInside method body, there are
statements.There is only one statement in the example.Each
statement should be ended with a semicolon ;One statement may span
multiple lines
Hello.java
1
/* The first program in Java
2
It simply prints out a message */
3
class Hello {
4
public static void main( String[] args ) {
5
// print message
6
System.out.println("Hello world\n");
7
}
8
}
XuanTung Hoang*
First Application: CommentsMulti-line comments with: /*
*/Single-line comments with: //Comments can be placed
anywhere.Comments are for human (compiler ignores comments)Comments
should explain the code
Hello.java
1
/* The first program in Java
2
It simply prints out a message */
3
class Hello {
4
public static void main( String[] args ) {
5
// print message
6
System.out.println("Hello world\n");
7
}
8
}
XuanTung Hoang*
More complex program: Addition
Addition.java
1
// Program that computes the sum of two numbers
2
import java.util.Scanner;
3
public class Addition {
4
public static void main( String args[] ) {
5
Scanner input = new Scanner( System.in );
6
int number1; // the 1st number
7
int number2; // the 2nd number
8
int sum; // sum of the two numbers
9
10
System.out.print("Enter the 1st number:");
11
number1 = input.nextInt();//read the 1st number
12
13
System.out.print("Enter the 2st number:");
14
number2 = input.nextInt();//read the 2nd number
15
16
sum = number1 + number2; // add numbers
17
// display result
18
System.out.printf( "Sum is %d\n", sum );
19
20
// display the result in another way
21
System.out.printf( "Sum is (again) %d\n",
22
number1 + number2 ); // display result
23
}
24
}
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More complex program: Additionimport statement specifies
external classes that we use in our programIn the example: Scanner
is the class we useScanner is a class in class libraries provided
by JDK
Addition.java
1
// Program that computes the sum of two numbers
2
import java.util.Scanner;
3
public class Addition {
...
...
24
}
XuanTung Hoang*
More complex program: AdditionVariables declarationUsing Scanner
object to read inputDo computation & display result
Addition.java
1
// Program that computes the sum of two numbers
2
import java.util.Scanner;
3
public class Addition {
4
public static void main( String args[] ) {
5
Scanner input = new Scanner( System.in );
6
int number1; // the 1st number
7
int number2; // the 2nd number
8
int sum; // sum of the two numbers
9
10
System.out.print("Enter the 1st number:");
11
number1 = input.nextInt();//read the 1st number
12
13
System.out.print("Enter the 2st number:");
14
number2 = input.nextInt();//read the 2nd number
15
16
sum = number1 + number2; // add numbers
17
// display result
18
System.out.printf( "Sum is %d\n", sum );
19
20
// display the result in another way
21
System.out.printf( "Sum is (again) %d\n",
22
number1 + number2 ); // display result
23
}
24
}
XuanTung Hoang*
Read input and display outputRead input with Scanner classImport
Scanner classimport java.util.Scanner;Create Scanner objectScanner
input = new Scanner( System.in );Read input from user using
nextInt() methodnumber1 = input.nextInt();Read textbook, section
2.5Display input with print, println, printfSystem.out.print(abc):
output the string abcSystem.out.println(abc): outputs the string
abc then goes to the next lineSystem.out.printf(result is %d, sum):
output a string with format specifiersRead textbook section 2.4
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Things to remember Java is case-sensitive: class and Class are
differentSkeleton of a classSkeleton of a class function
(method)Skeleton of a simple java programSimple Java program has
one class that contains main methodName of the source file must be
identical to the class name (class identifier)Statements end with
;Braces enclose blocks of codeBraces should go in pairs (Good
practice: Open and close brace together)Read input from user and
output result to screen
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Other experiencesObserve outputs of java compiler (javac.exe)
when compiling java program (.java file)When the compilation is
successfulWhat files are produced by javac.exeWhat is stored inside
those files (files produced by javac)When the compilation
failedSpecify the problem in your source code
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Variable and MemoryExample of variables:
A variable is associated with a location in memoryA variable
has:Name: is used to access the memory locationType (data type):
specifies how the variable is treated by the computerSize: The size
of the memory location; is determined according to type of the
variableValue: is stored in binary format at the memory
locationtypename
Scanner input = new Scanner( System.in );
int number1; // the 1st number
int number2; // the 2nd number
int sum; // sum of the two numbers
XuanTung Hoang*
Variable and Memory: Illustration
What does the following 16-bit string represent ?
00010100100000000
If you dont understand, please read textbook, section 2.6
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Primitive data types and ObjectsThere are many data typesWe can
even define our own data typeData types are classified into
primitive data types and reference types (objects)Primitives data
types: are most fundamental use small, fixed number of bytes are
built into Java are used as building block for developing more
complex data types (objects)There are 8 primitive data types:byte,
short, int, long, fload, double, char, boolean
Is Int a Java primitive data type ?Integral numbersFloating
point numberscharactersLogical (True/false)
Scanner input;
int number1; // the 1st number
int number2; // the 2nd number
int sum; // sum of the two numbers
XuanTung Hoang*
Number data typesNumber literalsValid integers:2007 2007L (long
integer)Valid floating point numbers:2007, 2007.02007f, 2007.1f
(float)2007d, 2007.1d (double)3.4E+3 (scientific notation) Can we
use byte data type to store the number 2007 ?
Integer Primitive Data Types
type
Size
Range
byte
8 bits
-128 to +127
short
16 bits
-32,768 to +32,767
int
32 bits
(about)-2 billion to +2 billion
long
64 bits
(about)-10E18 to +10E18
Floating Point Primitive Data Types
Type
Size
Range
float
32 bits
-3.4E+38 to +3.4E+38
double
64 bits
-1.7E+308 to 1.7E+308
XuanTung Hoang*
char data type and Character tableSize of char is 2 bytes (16
bits)Character table is used to map 16-bit codes to letters
(Unicode) Character literal:Valid characters:a, b, A, \n, \t
Is it a character C ?
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boolean data typeAccept only two values: true and falseThey are
Java keywords
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Expressions and Arithmetic ExpressionsExpression is a
combination of literals, operators and parenthesis to produce a
valueExample:a + b * c (a, b, c are variables already
declared)Expressions dealing with number variables and operators
are arithmetic expressionsArithmetic operators in Java: + , -, *,
/, %Be careful with division operator /:Integer division is
different from floating point division3 / 2 13.0 / 2 1.5How about
remainder operator with floating point numbers ?
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Order of calculation and PrecedenceOrder of
calculations:Parenthesis*, /, %+/-Left to rightExamples
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Equality and Relation operatorsEquality operators : ==,
!=Relational operators: , =See fig 2.14, section 2.8, textbook
Questions:Assume that we declare integer variable a and b and
assign values 3 to a, and 4 to b.Is a < b a valid expression
?What values are produced by a < b, a < b, a == b?
XuanTung Hoang*
Equality and relation operatorsBe careful when using == with
float/double variablesDoes this produce true ?4.0/3.0 == 1.0 +
1.0/3.0How about this ?1.0/3.0 = 0.333333333333333Floating point
arithmetic is NOT exactExact equality sometimes impossible to
achieve Logically we expect true but the computer report falseAvoid
using equality with floating point numbers
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Twos complement notation(Appendix E6, textbook)Assume 4-bit
signed integersArithmetic negation "-" is equivalent to "~" then +
1
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Floating-point number precisionTwo data type (primitive) for
floating point numbers: float and doublefloat: 32-bit (4-byte). Ex:
0.12fdouble: 64-bit (8-byte). Ex: 4.15dFloating-point numbers are
treated as double by defaultExample: 9.02 and 9.02d are all double
numbersFloating-point number arithmetic are approximate
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AssignmentAssignment operator, =Stores the value evaluated on
the right hand side into the variable on the left hand
sideExample:
int number1;
int number2;
int sum;
number1 = 4; // stores value 4 into variable number1
number2 = input.nextInt(); //get a number from user and stores
it into variable number2
sum = number1 + number2; // add number1 and number2 and stores
it into sum
