Transcript Introduction to Programming

Introduction to
Programming
Java Fundamentals
(Variables, Arithmetic, etc.)
David Goldschmidt, Ph.D.
Computer Science
The College of Saint Rose
Java Data Types
byte
1 byte
Integers in the range
-128 to +127
short
2 bytes
Integers in the range of
-32,768 to +32,767
int
4 bytes
Integers in the range of
-2,147,483,648 to +2,147,483,647
use double for your
floating-point numbers
long
8 bytes
Integers in the range of
-9,223,372,036,854,775,808 to +9,223,372,036,854,775,807
float
4 bytes
Floating-point numbers in the range of
±3.410E-38 to ±3.410E38, with 7 digits of accuracy
double 8 bytes
Floating-point numbers in the range of
±1.710E-308 to ±1.710E308, with 15 digits of accuracy
Variables

As in mathematics, a variable is a symbolic name
used to represent numeric (or other) values

In Java, variables must be declared and must have a
specific data type:
int x;
float y;
double average;
long q;
Assigning Values to Variables

Assign values to variables using the = operator:
int x;
float y;
double average;
long q;
x = 47;
y = -12.375F;
average = 42.7;
q = 875L;
Arithmetic Expressions

Rules to writing arithmetic expressions:

Two binary operators may not be next to one another
int result = 14 + * 87;

Parentheses form groupings and all expressions within
parentheses are evaluated first
int result = (7 + 10) * (11 – 1);
Arithmetic Expressions

More rules to writing arithmetic expressions:

Parentheses may be nested, meaning sets of parentheses
may be enclosed by other parentheses
int result = (2 * (4 – 8)) / 5;
evaluate inner parentheses first!

Parentheses cannot be used to indicate multiplication
int result = (7 + 10)(11 – 1);
Calculating Volume

How do we calculate the volume of a cylinder?

Volume V = r 2h

r
Given radius r and height h
h
How do we translate this equation to Java?
Calculating Volume

How do we calculate the volume of a cone?

Volume V = 13 r 2h

r
Given radius r and height h
h
How do we translate this equation to Java?
Using Mathematical Methods

What is a Java method?




A Java method is precompiled code that solves a problem
(e.g. calculates the square root) using an algorithm
A Java method accepts inputs
A Java method produces one output
Think of a Java method as a mathematical function
Calculating Square Roots

How do you calculate a square-root?

I don’t know! Let’s use Java’s Math class to do it:
sqrt() method expects
a double as input
public class SquareRoots
{
public static void main( String[] args )
{
System.out.print( "Square root of 81.0: " );
System.out.println( Math.sqrt( 81.0 ) );
System.out.print( "Square root of 90.27: " );
System.out.println( Math.sqrt( 90.27 ) );
}
}
Square root of 81.0: 9.0
output
Square root of 90.27: 9.501052
Calculating Square Roots

When using a method, answer these questions:




What are the expected inputs?
What are the data types of each input?
What is the expected output?
What is the data type of the output?
inputs
double x
output
Math.sqrt()
double Math.sqrt(x)
Operator Precedence

Operator Precedence specifies the order of evaluation:

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Evaluate expressions within parentheses first
(starting with innermost set of parentheses)
Evaluate methods (e.g. Math.sqrt(), Math.pow())
Perform all negations (e.g. result = x * -y)
Perform multiplication, division, and modulus operations


From left to right
Perform addition and subtraction operations

From left to right
Operator Precedence
double r = 1;
r = (19 – (-sqrt(4.0 + 5.0) / -r)) * (18 + 7 % 4 * 3 - 1);
r = (19 – (-sqrt(9.0) / -r)) * (18 + 7 % 4 * 3 – 1);
r = (19 – (-3.0 / -r)) * (18 + 7 % 4 * 3 – 1);
r = (19 – (-3.0 / -1)) * (18 + 7 % 4 * 3 – 1);
r = (19 – 3.0) * (18 + 7 % 4 * 3 – 1);
r = (16.0) * (18 + 3 * 3 – 1);
r = (16.0) * (18 + 9 – 1);
r = (16.0) * (26) =
416.0
Accumulating a Sum

Accumulating a sum has the following form:
int sum = 0;
int value = 12;
sum = sum + value;
evaluate the right-hand side first
then assign result to left-hand side variable
value = 18;
sum = sum + value;

Also note a shortcut form:
sum += value;
Counting by One

Counting by one has the following form:
sum = sum + 1;

And this shortcut form:
sum += 1;

And these shortcut forms:
sum++;
++sum;
Common Programming Errors

What are examples of programming pitfalls?

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Don’t rush to writing code until you have sketched out
an algorithm or solution
Create backups of your code using flash drives
Make sure every beginning has an end:
public static int void main(String[] args)
{
System.out.println("Quotes come in twos");
System.out.println("Answer: " + (9 + 5));
}
quotes
Common Programming Errors

More examples of programming pitfalls:



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Watch for misspelled Java keywords
Java is a case-sensitive language, so be careful of
uppercase and lowercase letters
Don’t forget to end statements with a semicolon (;)
Watch for incompatible data types when you assign
values to variables:
int x;
x = 928.502;
Common Programming Errors

Even more examples of programming pitfalls:

Watch out for integer division:
int result;
result = 1 / 2;

Don’t use a variable unless it has been declared and
assigned a value:
q = 928.502;
int x;
System.out.println(x);