COP 3331Object Oriented Analysis

and Design

Java Part I

Java Part I

// First Java Program// HelloWorld.javaPublic class HelloWorld { public static void main (String args[]) { System.out.println(“Hello World!”); }}

Java Part I

The following compile sequence occurs in Unix on Diablo.

• gaitrosd@diablo:~/java>javac HelloWorld.java• gaitrosd@diablo:~/java>java HelloWorld• Hello World!

Java Part I

File Definition Function

javac.exe The Java compiler

Converts Java source code into executable byte-code

java.exe The Java enterpreter

Runs the java program

appletview.exe The applet view Locally runs a java applet from within an HTML file.

jdb.exe The Java debugger

Used to debug your Java applications and applets

javah.exe The Java C header and stub file generator

Creates C header files and C stub files from a java class, allowing your java and C code to interact.

javap.exe The Java class file disassembler

Converts a compiled class back into source code.

javadoc.exe The Java API documentation generator

Generates HTML documentation from Java Source Code

Primary Java Program Files

Java Part I

• General Java points to remember:– Java is case sensitive. – Use ; (semicolon) to terminate

lines of code. – Use { } (curly braces) to indicate

blocks of code for classes, methods, if statements, and loops.

– Use spaces for indentation to make your code more readable.

Java Part I

Comment

Type Function

// C++ Everything after the // and until the end of the line is treated as a

comment.

/* */ C Everything between the /* and */ is treated as a comment even if it

crosses a line boundary.

/** */ Hypertext Same as the C style comments except that these comments are read by Java’s documentation

generator, which can generated HTML code from your

comments. You can include HTML code in these comments.

Java Part I

• Memory variables: Storage space declared inside the computer on memory is allocated through memory variables and constants.

• Java is strongly typed which means that memory variables can only hold their declared type of data.

• There are two types of data catetories:– Simple types.– Object types.

Java Part I

Type Size

byte 8 bits

char 16 bits (unsigned)

short 16 bits

int 32 bits

long 64 bits

float 32 bits

double 64 bits

boolean 1 bit

Simple data types are not based on any other type.These sizes do not vary from machine to machine. All numeric types are signed except character. Java is case sensitive. Names of simple data types Are in lower case as shown.

Simple Types

Java Part I

Declaring Variables

Format:

data_type variable_name;data_type variable_name =value;

Example:

int j; // integerchar opt; // charactershort I; // short integerlong L; // long integerfloat F; // real numberdouble D; // 64 bit real

numberboolean ok; // True/False

int I,j,k,l; char Men = “A”;

Java Part I

Operator Meaning Example- Unary negation x = -y;

+ Addition x= y + z + x;

- Subtraction x=y-z-x;

* Multiplication z = x * y;

/ Division z = x / y;

% Modulus n = x % 3;

++ Increment by 1 x++; ++y;

-- Decrement by 1 x--;

Note: There is not operator for exponent. You must use the Math.pow() function for this task.

Arithmetic Operators

Java Part I

Operator Meaning Example

!= Not Equal if(x != 100) y=Z;

< Less then if(x < 100) y=Z;

<= Less then or equal to if(x <= 100) y=Z;

> Greater then if(x > 100) y=Z;

>= Greater then or equal to

if( <= 100) y=Z;

! Not Answer = !Answer;

& And if( x=100 & y==0 ) y=Z;

| Or if( x=100 | y==0 ) y=Z;

^ Exclusive Or if( x=100 ^ y==0 ) y=Z;

&& Short circuit And if (x <3 && y==0) z=7;

|| Short circuit OR if (x <3 || y==0) z=7;

Comparison and logical Operators

On the short circuit operators, the next comparisonis not accomplished if it does not affect the outcome.

Java Part I

Operator Meaning Example

~ Bitwise compliment

x = ~x; //flips each bit.

& Bitwise And if(y&2 == 2)

| Bitwise Or x = 3|5; // result 7

^ Bitwise Xor x=3^5; // Result 6

<< Left Shift x = 1<<2; // Result 4

>> Sign propagating right shift

I = 8>> 2; // Result 2

>>> Zero-fill right shift

I = 8 >>>2;// result 2

Java Part I

Conditional Execution

if(condition)statement;

if(condition) { statement1;

statement 2;statemetn 3;etc;

}

Java Part I

if(condition) { statement1; statement2;

}else{ statement1;

statement2; }

Java Part I

Switch Statements

switch (expression)

{

case value1: statements;

case value2: statements;

. . .

default: statements;

}

switch (input_char) {

case ‘y’: System.out.print(“Entered y”);

case ‘n’: System.out.print(“Entered n”);

default: System.out.print(“Don’t know”);

}

Java Part ILoops

for (initialize; condition; increment)

{

statements;

statements;

}

example:

for (i=1; i<100; i++)

{

System.out.print(i);

}

Java Part I

while (condition)

{

statements;

statements;

}

while (J < 100) {

{

J = J + 1;

System.out.print(J);

}

Java Part I

Command Line Arguments: In all Java applications, the main() function accepts an argument, an array of strings called args[]; This array contains command line arguments.

For instance, if you entered the following on the HelloWorld program:

java HelloWorld Arg1 Arg2 “Hello Again”

The args.length would equal three (3). and the contents would be:

args[0] -> “Arg1”

args[1] -> “Arg2”

args[2] -> “Hello Again”