CMT4001 -- Programming Software Applications Week 2 Dr. Xiaohong Gao TP B107, ext. 2252 [email protected] Java Data Types and Operators

CMT4001 -- Programming Software Applications

Week 2

Dr. Xiaohong Gao

TP B107, ext. 2252

[email protected]

Java Data Types and Operators

Contents

To become familiar with Java applications

To become familiar with variables in Java

To become familiar with Java primitive’s data types

To become familiar with arithmetic operators

A Simple Program

1 // Fig. 2.1: Welcome1.java

2 // A first program in Java34 public class Welcome1 { 5 public static void main( String args[])6 {7 System.out.println( "Welcome to Java

Programming!" );8 }

9 }

Welcome to Java Programming!

A Simple Program: Printing a Line of Text


// indicates the remainder of the line is a comment• Comments are ignored by the compiler• Use comments to document and describe code

Can also use multiple line comments: /* ... *//* This is a multiple

line comment. It can

be split over many lines */

Another line of comments that describes the programNote: line numbers are not part of the program; they are added for our reference


3 A blank line•Blank lines and spaces make a program more readable•Blank lines, spaces, and tabs are known as whitespace •characters, and are ignored by the compiler

public class Welcome1 {

Begin a class definition for class Welcome1•Every Java program has at least one user-defined class•class keyword immediately followed by class name

–Keyword: words reserved for use by Java• Naming classes: capitalize every word

–SampleClassName


public class Welcome1 {Name of class called identifier

•Series of characters consisting of letters, digits, underscores ( _ ) and dollar signs ( $ )•Does not begin with a digit•Contains no spaces•Examples: Welcome1, $value, _value, button7•7button is invalid•Case sensitive (capitalization matters)

–a1 and A1 are differentFor now, use public keyword

•Certain details are not important now - mimic programs,• full discussions will come later


public class Welcome1 { Saving files

• File name is class name and .java extension• Welcome1.java

Left brace• Begins body of every class• Right brace ends definition (line 9)

public static void main( String args[] )

Part of every Java application•Applications begin executing at main

• Parenthesis indicate main is a method• Java applications contain one or more methods


5 public static void main( String args[] )• Exactly one method must be called main

Methods can perform tasks and return information• void means main returns no information• For now, mimic main's first line

6 {

Left brace begins body of method definition•Ended by right brace


System.out.println( "Welcome to Java Programming!" );

Instructs computer to perform an action•Prints string of characters between double quotes

–String - series characters inside double quotes•White spaces in strings are not ignored by compiler

System.out - standard output object•Allows java to print to command window (i.e., MS-DOS prompt)

Method System.out.println displays a line of text•Argument inside parenthesis

Entire line known as a statement•All statements must end with a semicolon ;


8 } Ends method definition

9 }

Ends class definitionSome programmers add comments to keep track of ending bracesLines 8 and 9 could be rewritten as:

8 } // end of the method main () 9 } // end of class Welcome1

Remember that the compiler ignores comments

A Simple Program


2 // Printing a line with multiple statements34 public class Welcome2 {

5 public static void main( String args[])6 {7 System.out.print ( "Welcome to Java);8 System.out.println(“Java programming”); 9 }

10 }System.out.print keeps the cursor on the

same line, so System.out.println continues

on the same line.

A Simple Program

Line numbers

1-2: Comments3: Blank4: Begin class Welcome25: Method main6: Begin main body7: Method System.out.print8: Method System.out.println9: end main10: end Welcome2


Escape characters– Backslash ( \ )– Indicates that special characters are to be output

• Backslash combined with a character makes an escape sequence

• \n - newline• \t - tab

Usage– Can use in System.out.println or System.out.print to create new

lines• System.out.println( "Welcome\nto\nJava\nProgramming!" );



2 // Printing multiple lines with just3 // a single statements45 public class Welcome3 {

6 public static void main( String args[])7 {8 System.out.print (“Welcome\9 \nto\nJava\nProgramming!”);10 } 11 }

Notice how a new line is output for

each \n escape sequence.

Welcometo

JavaProgramming!

Variables

A variable has three properties:

a memory location to store this value

the type of data stored in the memory location

the named used to refer to the memory location

Variables

The general syntax for declaring variables is:

<data type> <variables>

where variables is a sequence of identifiers separated by commas.

Example: int x; int y; or int x,y;

Variables

Variables – Variable names correspond to locations in the computer's memory– Every variable has a name, a type, a size and a value– Whenever a new value is placed into a variable it replaces (and

destroys) previous value – Reading variables from memory does not change them

Visual representation

number145

Data type

There are six numerical data types in Java:

• byte – integer• short –integer• int – integer• long –integer

• float – real• double - real

Example: int j, k, l; float numberOne, numberTwo; long bigInteger; double bigNumber;

Type Size Description

Integers

Real Numbers

Other Types

byte 8-bit Byte-length integershort 16-bit Short integerint 32-bit Integerlong 64-bit Long integer

floatdouble

32-bit64-bit

Single-precision floating-pointDouble-precision floating-point

charboolean

16-bit Unicode character

true or falseA single characterA boolean value(true or false)

Java’s primitive data types

Variables

Assignment statement

<variable> = <expression>;

Examples:

firstNumber = 234;

sum = firstNumber+ secondNumber;

solution = x*x-2*x+1;

Variables

int firstNumber,secondNumber;A after A is executed

firstNumber = 234;

secondNumber = 87;

firstNumber

secondNumber

The variables firstNumber and secondNumber are declared and set

in the memory

Variables

int firstNumber,secondNumber; after B is executed

firstNumber = 234;

secondNumber = 87;B

firstNumber

secondNumber

234

87

Values are assigned to thevariables firstNumber and secondNumber

Quick Check

Why are the following declarations all invalid?

int a, b, a;

float x, int;

float w, int x;

bigNumber double;

Another Java Application: Adding Integers

int number1; // first number to add int number2; // second number to add sum; // sum of number1 and number2

Declares variables number1, number2, and sum of type int•int can hold integer values (whole numbers): i.e., 0, -4, 97•Data types float and double can hold decimal numbers


// add the numbers

sum = number1 + number2;

Assignment statement

•First calculates sum of number1 and number2 (right hand side)•Next, uses assignment operator = to assign result to variable sum•Read as: sum gets the value of number1 + number2


System.out.printl(“The sum is”+ sum);

"The sum is " + sum•Uses the operator + to "add" the string literal "The sum is" and sum•Allows concatenation of a String and another data type

–Results in a new string•If sum contains 117, then "The sum is " + sum results in the new string "The sum is 117"•Note the space in "The sum is "

Arithmetic

Arithmetic calculations are used in most programs–Use * for multiplication and / for division, +, -

•No operator for exponentiation •Integer division truncates remainder7 / 5 evaluates to 1

–Modulus operator % returns the remainder 7 % 5 evaluates to 2

Operator precedence–Some arithmetic operators act before others (i.e., multiplication before addition)

•Use parenthesis when needed–Example: Find the average of three variables a, b and c

•Do not use: a + b + c / 3 •Use: (a + b + c ) / 3

Arithmetic

Operator(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.

Decision Making: Equality and Relational Operators

Standard algebraic equality operator or relational operator

Java equality or relational operator

Example of Java condition

Meaning of Java condition

Relational operators

> > 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

Equality operators

= == x == y x is equal to y

!= x != y x is not equal to y

<_

>_

=

Summary

• Java applications

• Variables in Java

• Java primitive’s data types

• Arithmetic operators

Documents

CMT4001 -- Programming Software Applications Week 2 Dr. Xiaohong Gao TP B107, ext. 2252 [email protected] Java Data Types and Operators