CMSC 150 INTRODUCTION TO COMPUTING CS 150: Fri 13 Jan 2012.
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CMSC 150INTRODUCTION
TOCOMPUTING
CS 150: Fri 13 Jan 2012
Variable Declarations
Use to request space in RAM to store values
Syntax: type variableName;
Types: int : whole number (e.g., 0, 1, 100,
1234) double : real-valued number (e.g.,
3.14159) char : one character (e.g., ‘A’, ‘9’,
‘q’) boolean : true or false String : character sequence (e.g.,
“Jason”)
Variable Declarations
Use to request space in RAM to store values
Syntax: type variableName;
Types: int : whole number (e.g., 0, 1, 100,
1234) double : real-valued number (e.g.,
3.14159) char : one character (e.g., ‘A’, ‘9’,
‘q’) boolean : true or false String : character sequence (e.g.,
“Jason”)
primitive types
Variable Declarations
Use to request space in RAM to store values
Syntax: type variableName;
Types: int : whole number (e.g., 0, 1, 100,
1234) double : real-valued number (e.g.,
3.14159) char : one character (e.g., ‘A’, ‘9’,
‘q’) boolean : true or false String : character sequence (e.g.,
“Jason”)
class type
Variable Declarations
Use to request space in RAM to store values
Syntax: type variableName;
Examples : int numberOfVictims; double minutesUntilDemise; char jasonsFirstInitial; boolean isKevinBaconStillAlive; String finalPleaForMercy;
In RAM
int numberOfVictims;
double minutesUntilDemise;
char jasonsFirstInitial;
boolean isKevinBaconStillAlive;
String finalPleaForMercy;
numberOfVictims
minutesUntilDemise
jasonsFirstInitial
isKevinBaconStillAlive
finalPleaForMercy
your programin memory
Assignment Statements
Use to put values into variables Syntax: variableName = expression;
Examples : numberOfVictims = 13; minutesUntilDemise = 2.1; jasonsFirstInitial = ‘J’; isKevinBaconStillAlive = false; finalPleaForMercy = “Help Me!”;
literals(type must
match variable
type)
In RAM
numberOfVictims = 13;
minutesUntilDemise = 2.1;
jasonsFirstInitial = ‘J’;
isKevinBaconStillAlive = false;
finalPleaForMercy = “Help Me!”
numberOfVictims
minutesUntilDemise
jasonsFirstInitial
isKevinBaconStillAlive
finalPleaForMercy
your programin memory
13
2.1
J
false
Help Me!
Declaration + Assignment
Combine into a single statement Syntax: type variableName =
expression;
Examples : int numberOfVictims = 13; double minutesUntilDemise = 2.1; char jasonsFirstInitial = ‘J’; boolean isKevinBaconStillAlive = false; String finalPleaForMercy = “Help Me!”;
Assignments & Expressions
numberOfVictims = 13;
numberOfVictims = numberOfVictims + 1;evaluate right-hand
side
value: 13
numberOfVictims
minutesUntilDemise
Assignments & Expressions
numberOfVictims = 13;
numberOfVictims = numberOfVictims + 1;
13
numberOfVictims
minutesUntilDemise
13
Assignments & Expressions
numberOfVictims = 13;
numberOfVictims = numberOfVictims + 1;
numberOfVictims
minutesUntilDemise
evaluate right-hand side
value: 13 + 1
13
Assignments & Expressions
numberOfVictims = 13;
numberOfVictims = numberOfVictims + 1;
14
numberOfVictims
minutesUntilDemise
14
Assignments & Expressions
numberOfVictims = 13;
numberOfVictims = numberOfVictims + 1;
numberOfVictims = numberOfVictims + 7; // party!
numberOfVictims
minutesUntilDemise
evaluate right-hand side
value: 14 + 7 14
Assignments & Expressions
numberOfVictims = 13;
numberOfVictims = numberOfVictims + 1;
numberOfVictims = numberOfVictims + 7; // party!
21numberOfVictims
minutesUntilDemise
21
Incrementing
Increment : add one to a variable
Three ways: numberOfVictims = numberOfVictims + 1; numberOfVictims += 1; numberOfVictims++;
All result in value increasing by one
Expressions
Numerical operators: + − * / %
Examples of expressions: 3.14159 + 2 (11 – 3) * 4 2 / 4 2.0 / 4 4 % 3 m * (c * c)
Expressions
Numerical operators: + − * / %
Examples of expressions (with variables): double piPlusTwo = 3.14159 + 2; double thirtyTwo = (11 – 3) * 4; double zero = 2 / 4; double oneHalf = 2.0 / 4; double remainder = 4 % 3; double e = m * (c * c);
Expression takes on type of largest-storage operand in expression
Examples of expressions (with variables): double piPlusTwo = 3.14159 + 2; double thirtyTwo = (11 – 3) * 4; double zero = 2 / 4; double oneHalf = 2.0 / 4; double remainder = 4 % 3; double e = m * (c * c);
Expression Type
Division
Works differently for integers vs. floating-point
Examples: 8.0 / 3.0 gives true floating-point result
8 / 3 gives integer quotient
8 % 3 gives integer remainder
Be Wary
double myShare = (1/2) * inheritance;
double onePointSixRepeat = (double)(5 / 3);
double threeFifths = 3/5; double wormHole = someValue / threeFifths;
Strings & String Methods
String homerSez = “Donuts. Is there anything they can’t do?”; 0123456789112345678921234567893123456789 0 0 0
int quoteLength = homerSez.length(); // 40 char firstChar = homerSez.charAt( 0 ); // ‘D’ char period = homerSez.charAt( 6 ); char questionMark = homerSez.charAt( 39 ); char eye = homerSez.charAt( homerSez.indexOf( ‘I’ ) );
String donutsCap = homerSez.substring(0, 6); // “Donuts” String donuts= donutCap.toLowerCase(); // “donuts”
String nuts = donuts.substring( 2 ); // 2 to end String nutsCubed = nuts + “ ” + nuts + “ ” + nuts + “!”;
Strings & String Methods
String homerSez = “Donuts. Is there anything they can’t do?”; 0123456789112345678921234567893123456789 0 0 0 int quoteLength = homerSez.length(); // 40 char firstChar = homerSez.charAt( 0 ); // ‘D’ char period = homerSez.charAt( 6 ); char questionMark = homerSez.charAt( 39 ); char eye =
homerSez.charAt( homerSez.indexOf( ‘I’ ) );
String donutsCap = homerSez.substring(0, 6); // “Donuts” String donuts = donutCap.toLowerCase(); // “donuts”
String nuts = donuts.substring( 2 ); // 2 to end String nutsCubed = nuts + “ ” + nuts + “ ” + nuts + “!”;
Digits
int one = 1; char uno = ‘1’; String ein = “1”;
All are different Only one contains the integer value 1
1 + 1 // 2 ‘1’ + ‘1’ // 98 (more on this later) “1” + “1” // “11”
Comments
Allow you to annotate your programs Two options:
inline // this is an example of an inline comment
block /* this is an example of a block comment */
Java does not execute comments
Use to describe (in English) what your code does
Also use to (temporarily) disable parts of code
public class ClassWithComments
{
public static void main( String[] args )
{
int numberOfVictims = 13; // number of people Jason has greeted
double minutesToDemise = 2.1; // mins from start of movie to 1st death
// Jason just met another person, so add one to # of victims
numberOfVictims = numberOfVictims + 1;
// Jason crashed a party, so really bump the victim count
numberOfVictims = numberOfVictims + 7;
/*
Let’s comment out the Kevin Bacon code for now...
Turns out that was just a dream sequence, but we might need
this code later!
// Jason killed Kevin Bacon’s character
numberOfVictims = numberOfVictims + 1;
*/
…
// Author: Kyra Sedgwick (you may need to search for the reference…)
// Date: 13 Friday 2012
// Purpose: This program keeps count of the number of victims of the
// “protagonist” Jason from the slasher movie “Friday The 13th”,
// along with some other interesting movie trivia.
public class ClassWithComments
{
public static void main( String[] args )
{
int numberOfVictims = 13; // number of people Jason has greeted
double minutesToDemise = 2.1; // mins from start of movie to 1st death
// Jason just met another person, so add one to # of victims
numberOfVictims = numberOfVictims + 1;
// Jason crashed a party, so really bump the victim count
numberOfVictims = numberOfVictims + 7;
…
/* Author: Kyra Sedgwick
Date: 13 Friday 2012
Purpose: This program keeps count of the number of victims of the
“protagonist” Jason from the slasher movie “Friday The 13th”,
along with some other interesting movie trivia.
*/
public class ClassWithComments
{
public static void main( String[] args )
{
int numberOfVictims = 13; // number of people Jason has greeted
double minutesToDemise = 2.1; // mins from start of movie to 1st death
// Jason just met another person, so add one to # of victims
numberOfVictims = numberOfVictims + 1;
// Jason crashed a party, so really bump the victim count
numberOfVictims = numberOfVictims + 7;
…
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