CISC1115 Notes - Professor Eva Cogan PDF

Preview

Summary

Professor Eva Cogan...

Description

8/30/18 

A class is a blueprint or template for creating different objects that defines properties and behaviors o Give examples from real life o An object is an instance of a class o Every source program includes only one class o We being class names with an uppercase letter o If a class is declared public the name of the source file must match the class name o Note the style 

Class header



Open brace at end of line



Close brace at the end of the program under the p

o Body of class is indented 

The body of anything is indented one tab



It is standard to use the tab key to indent.

o A method is a named set of statements o A block is 0 or more statements within braces o A string literal is a string of 0 or more characters enclosed in double quotes (what you are used to calling “quotation marks” o Println is a method o System.out.print sends output to the screen 

Everything is a Java Application



Every java app has a main method



Escape sequences



The \ is called the escape character and tells the computer to treat it as a special



We can use the escape sequence aka the back slash to print characters



\n is the new line character which takes it to a new line



\t is the tab character

Chapter 2 

Write a program to add 2 number /* Name: Add. Java Author: Jamal Description: add 2 numbers and print the result */ public class Add { public static void main (String [] args) { int number 1, number2, sum; number1 = 6; number2 = 7; sum = number1 + number2; System.out.println( “The Sum is “ + sum); } } /* Output

Handcheck

Trace

The Sum is 13

6+7=13

number1 number 2 sum 6

7

13

*/ 

A variable is a name for a physical location within the computer that can hold one value at a time. As the name implies, the value may change as the program is running



Give meaningful names



Declaration statement tells the computer which variables will be used in the program and what type of values they will hold



A variable of type int will hold an integer



A variable of type string will hold a string of characters Note: the upper case S



Keeping track of the value stored in each value stored in each variable is called tracing a program or producing a memory trace



We can print the value of a variable or an expression



We may declare and initialize a variable at the same time o Int number1 = 6, number2 = 7, sum; Int count, num = 4; //assigns 4 only to num



Suppose you want to store the price of an object in dollars and cents in a variable price. Price cannot have a data type int. to allow for the decimal places, we will declare price to have data type double. This data type allows the variable to hold a real number, one that may contain decimal places. o Double price; o Price = 3.50;



Float was the original. Hardly used anymore. You’ll see it in your workbook



Use double its double the size of float



Division gives decimal: price/2 is 1.75 5th grade division



If either or both operands are double , the division or float

Intro to java syntax 

Method A named sequence of statements



Class: for now a collection of related methos



Identifiers o The names of variables, methods, classes, packages and interfaces o A sequence of one or more characters. The first character must be a valid first character (letter,$,_). May also be followed by these or digits o Case sensitive o Style 

Variables, methods, keywords, packages use lower camelcase: uppercase only the first character of each word except the first



Classes (and thus files) use upper camelCase: uppercase the first character of each word



Literals 

A constant value in java o 100 an integer o 98.6 a floating point value o “this is a string” string



use () o to override precedence. Write y = a/b(+3) to add before dividing o to make a formula clearer o if you aren’t sure of the precedence



parentheses have highest precedence

9/4/18 

system is a class that provides methods related to the “system” or environment programs run



a package is a collection of related classes; java.io I/O stands for Input/output



data read by a program can come from 2 places: the keyboard or a data file



the system class also provides a special value System.in



scanner is a class that provides methods for inputting words,numbers, and other data



Scanner is provided by java.util



Import java.util.Scanner; is the main thing to put on top



Import statements can’t be inside a class definition



Create a scanner o Scanner in = new Scanner (System.in); o Declares a scanner variable named in and creates a new Scanner that takes input from System.in; o Often named in, sc, or scanner



Methods o Next – will return what comes before a space

o nextLine – automatically movesthe scanner down after returning the current line o nextInt – will return what comes before a space o nextDouble – will return what comes before a space. Convert to double 

Prompts o When the computer waits to read from the keyboard, the cursor blinks on the screen o Program doesn’t continue until user types something o Style: when the prompt and value are short, I put them both on one line



Program Structure o Java.util o Scanner o nextInt o hour = in.nextInt(); o hour*60 o hour



API (Application Programming Interface) o Standard edition of Java comes with several thousand classes



Docs.oracle.com/javase/8/docs/api/



Constants o Final double PI = 3.14159



Formatting output o Use the printf method to specify how values should be formatted

o Following comman displays price with 2 digits after decimal point





System.out.printf (“&.2f”. price);



You can also specify a field width 

System.out.printf(“%10.2f”, price)



The construct %10.2f is called a format specifier



“Hello%nWorld%n” Hello/World



Printf does not print to a new line, for new line use \n

Casting o Convert a floating point value to an integer is to use a type cast 

Double pi = 3.14159;



Int x = (int) pi;

o Type casting takes precedence over arithmetic operations it only applies to what follows immediately 

To solve nextLine being skipped after being asked age YOU MUST ADD A NEW nextLine TO SOLVE THE PROBLEM

9/6/18 

Standard input o System.in



Standard Output o System.out



Standard Error o System.err



Reading / Writing

o Import java.io.File; o Import java.io.PrintStream; o And add public static main (String [] args) throws Exception { o Try statement catches and handles the exception o Throws clause is that lists the exception 

An Exception is an event, which occurs during the program



Print to a file o Import. java.io.PrintStream; Import java.util.Scanner; Public class PrintToFile { Public static void main(String[] args) throws Exception { String first, last Scanner sc = new Scanner (System.in); PrintStream ps = new PrintStream (“Output.txt”); PrintStream ps = new PrintStream (newFile(“output.txt”)); System.out.println(“Please Enter your First and Last Name.”); Syste,.out.println(“Do not forget to press the enter key.”); First = sc.next(); Last = sc.next(); ps.println(“\nThis ismy First Program!”); ps.println(“My Name is: “ + first + “” + last); ps.close(); }

} 

Know how to read all versions o Note new File in new Scanner o Could put new File in PrintStream, too o Could also use PrintWriter instead of PrintStream o Should close file using ps.close(); User defined methods



o A module is a series of instructions with one specific purpose. A module can be written directly in the main program or we can write a method that consists of the named module o Methods can be called anytime throughout the program o A method can be called within main and another method can be called again 9/13/18 

Parameters and Arguments o Methods are possessive o Main has an n





Try to add one has an n



Value inside main method does not affect other n inside other methods

Multiple Parameters o Every time you call a method, you rewrite its trace from the beginning o The parameters and local variables exist only while the method is executing and are destroyed when you return to the calling method

o Parameters are matched by position, not by name o Call by value: in method java method arguments are passed by value o Before each method, put a comment saying what it does 

Increment operator o Java provides a more concise way to add and subtract by one. Specifically ++ is the increment o Decrement is –

9/20/18 

Assignment operators have lowest precedence and associate right to left.



Booleans are variables that can hold both true and false



A conditional if statement allows a program to branch, which means to allow the path of execution depending on the value



In a conditional statement, the keyword if is followed by some condition (in parentheses) that evaluates to either true or false



Three rules o If true, execute o If false, ignore o If more than one statement in the body, enclose the block of statements in curly braces{}



Style o If its only one statement, I don’t put braces some people do o Put the open brackets at the end f the header and the close brace under the ‘I’

o Put the if condition on one line and the body on the next line, indented one tab position (like the body of anything) 

Note: o Indent one tab for body o Braces if the body is a block of compound statements o No ; after else

9/27/18 

The chained If-else o We can use a chain of if-else construction o Java lets you chain multiple if-else statements together for situations where you need to choose one of multiple statements to execute o Quit as soon as we find a match o Simplest form of a chained if





If cond1 is true, it does st_1



If cond1 is false and cond2 is true, st 2 is executed



If cond1 is false and cond2 is false, st_3 is executed



St 4 is always executed

Dangling if-else o An else statement is associated with the closest preceding unmatched if. Use {} to enforce what you mean



For loop o For(int I = 1, i...