COP 3331 Object Oriented Analysis and Design Java

COP 3331 Object Oriented Analysis and Design Java Part I

Java Part I // First Java Program // Hello. World. java Public class Hello. World { 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 Hello. World. java • gaitrosd@diablo: ~/java>java Hello. World • Hello World!

Java Part I Primary Java Program Files 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

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 Commen Type t // /* */ /** */ 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 Simple Types 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.

Java Part I Declaring Variables Format: data_type variable_name; data_type variable_name =value; Example: int j; char opt; short I; long L; float F; double D; boolean ok; // // int I, j, k, l; char Men = “A”; integer character short integer long integer real number 64 bit real number True/False

Java Part I Arithmetic Operators Operator Meaning Example - Unary negation x = -y; + Addition - 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--; x= y + z + x; Note: There is not operator for exponent. You must use the Math. pow() function for this task.

Java Part I Comparison and logical Operators 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; On the short circuit operators, the next comparison is 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) { statement 1; statement 2; statemetn 3; etc; }

Java Part I if(condition) { statement 1; statement 2; } else { statement 1; statement 2; }

Java Part I Switch Statements switch (expression) { case value 1: statements; case value 2: 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 I Loops for (initialize; condition; increment) { statements; } example: for (i=1; i<100; i++) { System. out. print(i); }

Java Part I while (condition) { 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 Hello. World program: java Hello. World Arg 1 Arg 2 “Hello Again” The args. length would equal three (3). and the contents would be: args[0] -> “Arg 1” args[1] -> “Arg 2” args[2] -> “Hello Again”