Intro to CS – Honors IProgramming BasicsGEORGIOS PORTOKALIDIS

GPORTOKA@STEVENS.EDU

Overview Object-oriented programming basics

Algorithms

Java fundamentals◦ Variables◦ Data types◦ Arithmetic operators◦ Operator precedence

Object-Oriented Programming Objects

◦ They are all around us◦ Cars, people, trees…

Each object can perform certain actions◦ Independently or interacting with other objects◦ These actions are called methods

Each objects has characteristics or attributes◦ Example: a car has static attributes like its color and dynamic attributes like its speed

A class defines the type or kind of object◦ Example: all car objects could belong to the automobile class

Objects belonging to a particular class have similar attributes, but are not the same!

Object-Oriented Languages What other OOP languages do you know?

OOP Design Principles Encapsulation

◦ Putting things into a capsule◦ The capsule hides what’s inside

◦ AKA information hiding

◦ Part of the capsule is exposed◦ Applies to all programming

◦ OOP languages help you enforce the separation

Polymorphism◦ Means “many forms”◦ For Java it means that the same method can cause

differently actions based on the object it is used with◦ Example: the accelerate method of all objects in the automobile class,

will accelerate the vehicle, but may do so in a very different way

Inheritance◦ A way of organizing classes

Capsule

ImplementationAttributes

Methods

Ferrari Tesla

accelerate accelerate

The user knows he just wants to accelerate

Inheritance

Generic class

More specializedclasses

Even more Specialized classes

Algorithms An algorithm is a set of directions for solving a problem How can you express an algorithm?

◦ In English◦ In a programming language◦ In pseudocode

◦ A combination of the above

Come up with an algorithm for ordering N numbers from lowest to highest and write it in pseudocode

Variablespublic class EggBasket{

public static void main(String[] args){

int numberOfBaskets, eggsPerBasket, totalEggs;

numberOfBaskets = 10;eggsPerBasket = 6;totalEggs = numberOfBaskets * eggsPerBasket;

System.out.println("If you have");System.out.println(eggsPerBasket + " eggs per basket and");System.out.println(numberOfBaskets + " baskets, then");System.out.println("the total number of eggs is " + totalEggs);

}}

Variables are used to store data

Values can be assigned to variables

Variables are of a type

SYNTAX

Type Variable_Name_1, Variable_Name_2, ...;

Data Types Determine how much memory will be required for the data and how the data are stored in memory

Java has two main types◦ Primitive types◦ Classes

Identifiers Identifier is the technical term for a name

In Java it can contain:◦ Letters◦ Digits◦ The underscore character (_)

Cannot begin with a digit

Case sensitive

Cannot be keywords?

public static void main(String[] args)

{int 1st_number,

secondNumber,

secondnumber;

Example

An identifier cannot begin with a digit

Naming Conventions Avoid words frequently used with other meanings

◦ Example: println and main

Multiple conventions◦ Pick one and be consistent◦ Example:

◦ Variables should begin with a lowercase letter,◦ Names composed by multiple words should have the first letter of every word besides the first capitalized◦ numberOfBaskets, eggsPerBasket, totalEggs

Constants Constants or literals are data that, unlike variables, cannot change

numberOfBaskets = 10;

pi = 3.14159;

firstInitial = 'B';

Constants also have a type. What is the type of these?

Floating-Point Numbers Scientific notation: number 865000000.0 can be written as 8.65 × 108

Java’s e notation or floating-point notation: 8.65e8

Example:

0.000483 4.83x10-4 3.83e-4

Is 5.0 the same as 5?

Floating point numbers are stored with limited precision

0.3333 … -> Is stored as exactly 0.3333333333

Includes decimal pointSingle digit before decimal point

Exponent cannot include decimal point

Named Constants Variables with a constant value

public static final Type Variable = Constant;

Examples:◦ public static final double PI = 3.14159;◦ public static final int DAYS_PER_WEEK = 7;

Assignments SYNTAX

Variable_name = Expression;

EXAMPLE

score = goals – errors;

interest = rate * balance;

number = number + 5;

An expression can be many things. We will learn many different expressions as we go.

Arithmetic expressions.

Assignment Compatibilities “You can’t put a square peg in a round hole”

byte → short → int → long → float → double

Where is char?

Type Casting What happens here?

double distance = 9.56;

int points = distance;

How about now?

double distance = 9.56;

int points = (int)distance;

System.out.println(points);

Numbers are not rounded!

Assignment is illegal

The typecast transforms the value to the type: double->int

Arithmetic Operators Five binary operators (between two operands)

◦ Addition +◦ Can also be used as an unary operator to negate a number

◦ Subtraction –◦ Can also be used as an unary operator to negate a number

◦ Multiplication *◦ Division /

◦ Integer division does not produce a floating-point result later being cast to an integer

◦ Remainder %◦ When performing an integer division

The type of the result is the same as the “largest” of the two operands

◦ byte → short → int → long → float → double

balance + deposit

balance * rate

11 / 3

11 % 3

Other Unary Operators Increment/decrement operators: ++, --

◦ Increase/decrease value of variable by one

Can be used as a prefix or suffix◦ As prefix to a variable it first applies the operator to it, and then returns its value◦ As suffix to a variable it returns its value, and then operator on it

Can also be used independently: ++n;

What is the value of d and n?◦ n = 10; d = 5 + ++n;

What is the value of n, b, and d;◦ n = 3; b = 5; d = ++b - n--;

Operator Precedence From highest to lowest

◦ Unary operators ++, --, +, -◦ Binary operators *, /, %◦ Binary operators + and –

Parentheses can be used to change the priority of operations

Example: d = (n + 10) * 2

What is the result of this d = 5; d = ++d + (--d * 4); ?

Special Operators II You can precede the = assignment operator with arithmetic operators

Example: d += 10; is the same as d = d + 10;

Are these the same?

d = 5;◦ d = d * 5 + 5;◦ d *= 5 + 5;

Operator precedence from highest to lowest◦ Unary operators ++, --, +, -◦ Binary operators *, /, %◦ Binary operators + and –◦ Special operators +=, *=, etc.

Bitwise Operators Bitwise operators:

◦ AND &◦ OR |◦ XOR ^

Operator precedence from highest to lowest◦ Unary operators ++, --, +, -◦ Binary operators *, /, %◦ Binary operators + and –◦ Bitwise &, ^, |

Shift Operations Java has no unsigned numbers

Numerical shift◦ Left <<◦ Right >>

Logical shift is still possible◦ Left <<<◦ Right >>>

Operator precedence from highest to lowest◦ Unary operators ++, --, +, -◦ Binary operators *, /, %◦ Binary operators + and –◦ Shift operators◦ Bitwise &, ^, |