CIS 260: App Dev I

2 Programs and Programming n Program  A sequence of steps designed to accomplish a task n Program design  A detailed _____ for implementing a program n Programming  The process of implementing a program design n Application program  A stand-alone computer program that is applied to a real-world problem plan

3 The Java Programming Language n Programming language  The ________ used to create valid program statements n Syntax  The symbols, words, and rules of a programming language n A simple Java program public class Welcome { public static void main(String[] args) { System.out.println("Welcome to Java Programming"); } syntax

4 The Java Syntax n Tokens  Special symbols, word symbols, and __________ of a language n Special symbol  One or more characters w/ special meaning  Examples: +, -, *, /, <, … n Word symbols  Reserved word (___________)  Examples: int, static, return, true, … n Identifier  Predefined or user-defined names of things  Examples: print, totalCost, … identifiers keyword

5 Data Types n Data type  A classification of data according to legal values and legal operations on those values n Primitive data types in Java primitive characternumericlogical integralfloating-point charbyteshortintlongfloatdoubleboolean

6 Details on Selected Data Types n char  Examples: ‘A’, ‘a’, ‘$’, ‘&’, ‘ ’, …  Unicode 65 is ‘A’ and Unicode 43 is ‘+’ n int  Non-decimal (whole number) values  Range of values: to  Examples: 24, -117, 34082, 0, … n double  Decimal values with up to 15 decimal places (double precision)  Range of values: -1.7 x to 1.7 x  Examples: 14.75, , , -5.3E-4 n boolean  Logical values  Examples: true, ___________ false

7 Arithmetic Operators n Possible arithmetic operators for integral and floating- point data types:  +, -, *, /, % n Examples  8+7 yields 15  6-15 yields -9  6*8 yields 48  6*8.0 yields 48.0  15/4 yields _____  15/4.0 yields 3.75  15%7 yields 1  15.2%7 yields _____

8 Order of Precedence *, /, and % have the same precedence + and – have the same precedence, but lower than *, /, and % n Operations with the same precedence are performed from left to right () ’s can be used to override normal precedence n Examples  / 2 % 3 yields ____  (4 + 8 / 2) % 3 yields ____ 5 2

9 Expressions n Integral expressions  All operands are integers or integer types  Example: (apples + oranges) * 2 n Floating-point expressions  All operands are floating-points or floating-point types  Example: totalCost *.05 n Mixed expressions  Operands are of different types  Examples: 2*5/mpg yields ______ if mpg is 4.0 ( double ) cost/2+(7-10.0) yields _______ if cost is 3 ( int )

10 Type Casting n Implicit type coercion  Occurs automatically with mixed expressions  15/4.0 automatically becomes 15.0/4.0 n Explicit type conversion  Also called type _________  Converts a result to a desired data type  Examples (double) 15/3 yields ______ (int) (16/3.0)+2*8%5 yields ______ ( int) 16/number + 7 yields _____ if number is 2.0 (char) 65 yields ______ casting 6 15 ‘A’ 5.0

11 The class String A string is a sequence of 0 or more characters enclosed in double ________ (e.g., “Joe” ) In Java, a String is not a primitive data type A String with no characters is called a _____ string ( “” ) n The length of a String is its number of ___________ The position of a character in a String starts with 0 for the first, 1 for the second, … quotes null characters

12 Parsing Numeric Strings n In Java, input can only be received as a string or character n A string with only integers or decimal numbers is called a ________ string (e.g. “78.3”, “.0038”, “17”) n To convert a numeric string to an actual number in Java  Integer.parseInt(“17”) yields ____  Double.parseDouble(“78.3”) yields ____  Integer.parseInt(numInput) yields ____ numeric ???

13 Variables and Named Constants n How to store program data in main memory:  Write a statement to ___________ memory  Write a statement to put data in memory location n Data that may change during program execution are stored in a ___________.  int hoursWorked; // allocates memory  hoursWorked = 45; // puts data in  int overtimeHours = 5; // does both n Data that should not change during program execution are stored in a named ___________.  final double PAY_RATE = 7.50; Variables and constants are just __________ locations. allocate variable constant memory

14 Assignment Statements n _______ variables in Java (allocate memory):  double cost;  String firstName, lastName;  int i, j, k; n ________ variables in Java (store in memory):  cost = 19.95;  firstName = “Richard”;  i = i + 1; // get i, add 1, store in i n The “=“ is an _________ operator, not “equals”. It literally means “is assigned the value”. n Assign a new value to an existing variable:  cost = materiaCost + laborCost; Declare Assign assignment

15 Input (Read) Statement in Java n Java is a pure OO language and uses its own special classes, objects, and methods. The two Java statements below use the BufferedReader and ___________________ classes and the ___ object of the System class to create an object called keyboard, which uses a predefined method called readLine() to store characters in a variable called name : BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in)); name = keyboard.readLine(); n To convert string data to numeric data:  price = Double.parseDouble(keyboard.readLine()); InputStreamReader in

16 Increment and Decrement n The following type of statement is used a lot:  count = count + 1;  It means “get the value in count, add 1 to add, assign it to count”  A shortcut in Java: count++; or ++count; n Increment and decrement operators have prefix and _______ forms.  The prefix form is evaluated before the expression is evaluated.  The postfix form is evaluated ______ the expression is evaluated. n Example: int a=0, b=0, c; c = 2 + (++a); // ___ will be stored in c c = a + (b++); // ___ will be stored in c c = a + (++b); // ___ will be stored in c postfix after 3 1 3

17 Using the String Class n A String object usually consists of one or more __________. String title = “War and Peace”; n The following shows an empty String and a null String:  String code = “”;  String inputValue = null; n _______ sequences use the \ to create new lines, tabs, or special characters. “\”Bud\”\tSmith \n Rick\tAnkiel”  “Bud”Smith RickAnkiel characters Escape

18 String Class Methods/Joining n A method of a class is called using the object name, a ____, and the method name (with arguments). String choice=“X”; if (choice.equals(“x”)) // returns false n How to join (____________) String objects: String title = “War and Peace”; double price = 14.95; String message = “Title: ” + title + “\n” + “Price: ” + price; n Note the code is written to enhance readability. dot concatenate

19 Output In Java, the standard output object is __________ with methods print and _______. print leaves the cursor at the end of the current line while println moves it to the next line. n System.out.println(‘q’);// displays q n System.out.println(“Joe”);// displays Joe Escape sequence \n is for a new _____, \t is for a _____. n Example String name = “Joe”; System.out.println(“My name is \n” + name + “.”); System.outprintln line tab

20 Packages and import n In Java, a package is a collection of related ________. n A class is a section of Java code in a file that contains methods and data definitions. n A method is a set of instructions to accomplish a specific _____. n The package _________ contains classes for program input and output. To make all classes in java.io available in your program you need the statement ________________ at the very beginning. classes task java.io import java.io

21 Java Application Programs n Your Java application program must contain at least one class and one of those classes must have a method called ______. n The method main has two parts:  The heading: public static void main(String [] args) –public means main is accessible to other classes –static means main isn’t directly related to objects –void means main will not return data  The body Enclosed in { } ’s Contains declaration statements: int myAge, yourAge; Contains executable statements: myAge = 50; main

22 Programming Style and Form n ________ rules must be followed. For example,  You must place a “ ; ” at the end of each program statement  { } ‘s must always occur in pairs n Form and style:  Write just one statement per line  Indent lines for readability (as shown in examples)  Add important _____________ using // and /* … */ Always begin a program with comments for the program name, the programmer, the date, and the program purpose  Naming variables ( hourlyWage ), constants ( TAX_RATE )  Provide prompt lines for input  Provide good explanation for output Syntax documentation

A Java Application Program /* * Conversion.java * Created by Malik & Nair * 9/3/04 * Convert inches to centimeters */ import java.io.*; public class Conversion { static BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in)); static final double CONVERSION = 2.54; static final int INCHES_PER_FOOT = 12; public static void main (String[] args) throws IOException { //declare variables int feet, inches, totalInches; double centimeter; // get input from user System.out.println("Enter feet: "); feet = Integer.parseInt(keyboard.readLine()); System.out.println(); System.out.println("Enter inches: "); inches = Integer.parseInt(keyboard.readLine()); // process data totalInches = INCHES_PER_FOOT * feet + inches; centimeter = totalInches * CONVERSION; // display output to user System.out.println("\nThe numbers you entered are " + feet + " for feet " + "and " + inches + " for inches. "); System.out.println("\nThe total number of inches = " + totalInches); System.out.println("The number of centimeters = " + centimeter); }