Transcript double

Week 4 - Friday
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What did we talk about last time?
Examples
switch statements
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History of computers
Hardware
Software development
Basic Java syntax
Output with System.out.print()
Mechanical Calculation Devices (2400BC onward)
• Aid to human calculation
• No stored program
Mechanical Computers (1725 onward)
• Punch card programming
• Serious limitations
Early Electronic Computers (1941 onward)
• General purpose, stored program computers
• Electronic, using vacuum tubes
Microprocessors (1970's onward)
• Succeeded transistors
• Now billions of computations per second at a nanometer scale
Cache
• Actually on the CPU
• Fast and expensive
RAM
• Primary memory for a desktop computer
• Pretty fast and relatively expensive
Flash Drive
• Faster than hard drives
• Most commonly on USB keychains
Hard Drive
• Secondary memory for a desktop computer
• Slow and cheap
Optical Drive
• Secondary memory that can usually only be written once
• Very slow and very cheap
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Storage for all the data and instructions on
your computer
Modern computers store everything as binary
digits (bits) which have a value of 0 or 1.
1 byte
= 8 bits
1 kilobyte (kb)
= 210 bytes
1 megabyte (mb)
= 220 bytes
1 gigabyte (gb)
= 230 bytes
1 terabyte (tb)
= 240 bytes
Monitor
• Common visual output device
Speakers
• Common audio output device
Mouse
• Common input device
Keyboard
• Common input device
Source
Code
Machine
Code
Computer!
Solve a
problem;
010101010
010100101
001110010
Hardware
Execute
Java
Source
Code
class A
{
Problem p;
p.solve();
}
Java
Bytecode
Machine
Code
101110101
010101010
101011010
110010011
JVM
010100101
001110010
Hardware
Often goes through phases similar to the
following:
1. Understand the problem
2. Plan a solution to the problem
3. Implement the solution in a programming
language
4. Test the solution
5. Maintain the solution and do bug fixes
Factor of 10 rule!
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The absolute smallest program possible, with
a print statement
public class Hello
{
public static void main(String[] args)
{
System.out.println("Hello, world!");
}
}
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For example, instead of one print statement,
we can have several:
System.out.println("Hello, world!");
System.out.println("Hello, galaxy!");
System.out.println("Goodbye, world!");
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Each statement is an instruction to the
computer
They are printed in order, one by one
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Java is a case sensitive language
Class is not the same as class
System.out.println("Word!");
prints correctly
system.Out.Println("Word!");
does not compile
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Java generally ignores whitespace (tabs,
newlines, and spaces)
System.out.println("Hello, world!");
is the same as:
System.out.
println(
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"Hello, world!");
You should use whitespace effectively to
make your code readable
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There are two kinds of comments (actually 3)
Single line comments use //
System.out.println("Hi!"); // this is a comment
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Multi-line comments start with a /* and end
with a */
System.out.println("Hi!"); /* this is
a multi-line
comment */
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Binary representation
Basic data types
Using Scanner for input
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The binary number system is base 2
This means that its digits are: 0 and 1
Base 2 means that you need 2 digits to
represent two, namely 1 and 0
Each place in the number as you move left
corresponds to an increase by a factor of 2
instead of 10
Sixty fours
256’s
Sixteens
Fours
1024’s
11111100000
512’s
Twos
128’s
Eights
Thirty twos
Ones
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We're focusing on five basic types of data in Java
These are:
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int
double
boolean
char
String
For whole numbers
For rational numbers
For true or false values
For single characters
For words
String is a little different from the rest, since
you can call methods on it (and for other
reasons)
Type
Kind of values
Sample Literals
int
Integers
-5
0
900031
double
Floating-point
Numbers
3.14
-0.6
6.02e23
boolean
Boolean values
true
false
char
Single characters
'A'
'Z'
'&'
String
Sequences of
characters
"If you dis Dr. Dre"
"10 Sesquipedalians"
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The int type is used to store integers
(positive and negative whole numbers and
zero)
Examples:
 54
 -893992
0
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Inside the computer, an int takes up 4 bytes
of space, which is 32 bits (1's and 0's)
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You will use the int type very often
Sometimes, however, you need to represent
numbers with a fractional part
The double type is well suited to this
purpose
Declaration of a double variable is just like
an int variable:
double x;
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Numbers are great
But, sometimes you only need to keep track
of whether or not something is true or false
This is what the boolean type is for
Hopefully you have more appreciation for
booleans now
Declaration of a boolean variable is like so:
boolean value;
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Sometimes you need to deal with characters
This is what the char type is for
The char type only allows you to store a
single character like '$' or 'q'
Declaration of a char variable is like so:
char c;
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The String type is different from the other
types in several ways
The important thing for you to focus on now
is that it can hold a large number of chars,
not just a single value
A String literal is what we used in the
Hello, World program
String word;
There are three parts to using Scanner for
input
1. Include the appropriate import statement so
that your program knows what a Scanner
object is
2. Create a specific Scanner object with a name
you choose
3. Use the object you create to read in data
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Lots of people have written all kinds of useful
Java code
By importing that code, we can use it to help
solve our problems
To import code, you type import and then the
name of the package or class
To import Scanner, type the following at the
top of your program (before the class!)
import java.util.Scanner;
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Once you have imported the Scanner class,
you have to create a Scanner object
To do so, declare a reference of type Scanner,
and use the new keyword to create a new
Scanner with System.in as a parameter like
so:
Scanner in = new Scanner(System.in);
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You can call it whatever you want, I chose to call
it in
Doesn't make any sense? For now, that's okay.
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Now that you've got a Scanner object, you can
use it to read some data
It has a method that will read in the next piece of
data that user types in, but you have to know if
that data is going to be an int, a double, or a
String
Let's say the user is going to input her age (an
int) and you want to store it in an int variable
called years
We'll use the nextInt() method to do so:
int years;
years = in.nextInt();
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Scanner has a lot of methods (ways to
accomplish some tasks)
For now, we're only interested in three
These allow us to read the next int, the next
double, and the next String, respectively:
Scanner in = new Scanner(System.in);
int number = in.nextInt();
double radius = in.nextDouble();
String word = in.next();
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Numerical operations
Advanced math operations
boolean operations
char operations
String operations
Wrapper classes
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+ adds
- subtracts
* multiplies
/ divides (integer division for int type and
fractional parts for double type)
% finds the remainder
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Order of operations holds like in math
int
int
int
int
a
b
c
d
=
=
=
=
31;
16;
1;
2;
a = (((b + c) * d) – a / b) / d;
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You can use parentheses to clarify or change
the precedence
Now a is 16
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You cannot directly store a double value
into an int variable
int a = 2.6; // fails!
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However, you can cast the double value to
convert it into an int
int a = (int)2.6;// succeeds! (a = 2)
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Casting tells the compiler that you want the
loss of precision to happen
You can always store an int into a double
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The sin() method allows you to find the
sine of an angle (in radians)
This method is inside the Math class
The answer that it gives back is of type
double
To use it, you might type the following:
double value = Math.sin( 2.4 );
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In Java, the conversion of a double into an
int does not use rounding
As in the case of integer division, the
fractional part is dropped
For positive numbers, that's like using floor
For negative numbers, that's like using
ceiling
The right way to do rounding is to call
Math.round()
double x = 2.6;
int a = (int)Math.round(x);
// rounds
Return type
Name
Job
double
sin( double theta )
Find the sine of angle theta
double
cos( double theta )
Find the cosine of angle theta
double
tan( double theta )
Find the tangent of angle theta
double
exp( double a )
Raise e to the power of a (ea)
double
log( double a )
Find the natural log of a
double
pow( double a, double b )
long
round( double a )
Raise a to the power of b (ab)
Round a to the nearest integer
double
random()
double
sqrt( double a )
double
toDegrees( double radians )
Convert radians to degrees
double
toRadians( double degrees )
Convert degrees to radians
Create a random number in [0, 1)
Find the square root of a
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! NOT
 Flips value of operand from true to false or
vice versa
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&& AND
 true if both operands are true
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|| OR
 true if either operand is true
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^ XOR
 true if operands are different
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In some circumstances, Java doesn't check the
whole expression:
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(true || (some complicated expression))
 Ignores everything after || and gives back true
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(false && (some complicated expression))
 Ignores everything after && and gives back false
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char values can be treated like an int
int number;
number = 'a';
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// number contains 97
It can be more useful to get the offset from a
starting point
char letter = 'r';
int number;
number = letter – 'a' + 1;
//number is 18
Remember that we use single quotes to designate a
char literal:
'z'
 What if you want to use the apostrophe character ( ' )?
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 apostrophe:
'\''
 tab:
 newline:
'\t'
'\n'
What if you want to use characters that can't be
printed, like tab or newline?
The backslash is a message that a special command
called an escape sequence is coming
 These can be used in String literals as well:
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 "\t\t\t\nThey said, \"Wow!\""
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The only operator that we will use directly
with Strings is the + (concatenation)
operator
This operator creates a new String that is
the concatenation of the two source Strings
Concatenation can be used to insert the values
of other types into Strings as well
String word;
word = "tick" + "tock"; // word is "ticktock"
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equals()
 Tests two Strings to see if they are the same
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compareTo()
 Returns a negative number if the first String comes earlier in
the alphabet, a positive number if the first String comes later
in the alphabet, and 0 if they are the same
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length()
 Returns the length of the String
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charAt()
 Returns the character at a particular index inside the String
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substring()
 Returns a new String made up of the characters that start at
the first index and go up to but do not include the second index
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Each primitive data type in Java has a wrapper
class
 Integer
▪ Allows String representations of integer values to be
converted into ints
 Double
▪ Allows String representations of floating point values to be
converted into doubles
 Character
▪ Provides methods to test if a char value is a digit, is a letter,
is lower case, is upper case
▪ Provides methods to change a char value to upper case or
lower case
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Making choices with if statements
 Basics
 Having if bodies with more than one line
 Using else blocks
 Nesting if statements
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Using switch statements
Any
boolean
The if part
expression
if( condition )
statement;
Any single executable
statement
if( condition )
statement1;
else
statement2;
Two different
outcomes
if( condition )
{
statement1;
A whole statement2;
bunch of
statements …
statementn;
}
if( condition1 )
{
statement1;
if( condition2 )
{
if( condition3 )
statement2;
…
}
}
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The most common condition you will find in an
if is a comparison between two primitive types
In Java, that comparison can be:
 ==
 !=
 <
 <=
 >
 >=
equals
does not equal
less than
less than or equal to
greater than
greater than or equal to
switch( data )
{
case value1:
statements 1;
case value2:
statements 2;
…
case valuen:
statements n;
default:
default statements;
}
Both "Three"
int data = 3;
and "Four"
switch( data )
{
are printed
case 3:
System.out.println("Three");
case 4:
System.out.println("Four");
break;
case 5:
System.out.println("Five");
The
}
break is
The default
is optional too
optional
1.
2.
3.
4.
5.
6.
The data that you are performing your
switch on must be either an int, a char,
or a String
The value for each case must be a literal
Execution will jump to the case that
matches
If no case matches, it will go to default
If there is no default, it will skip the whole
switch block
Execution will continue until it hits a break
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Exam 1
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Study for Exam 1
Keep working on Project 1, due tonight by
11:59!
 Never look at another student's code