Slide 1
CSCI1227Computer Programming andProblem Solving Lecture 2: 1226
Review Tami MeredithProgramming ProcessHow do we fill in the yellow
box?TextEditorCompiler(javac)Interpreter (JVM:
java)UserLibrariesOperating System
(Windows)OutputInputJDKProgramming RequiresIdentification of the
problemUnderstanding it, identifying correct solutionsSolving the
problem:Selecting the data structures, andData Management is the
key hereIdentifying an algorithmControl Flow is the basis of
algorithmsCoding the solutionTesting, debugging, verifying the
solutionWhat is a Program?Programs = Data + AlgorithmsData: the
nouns, the things we manipulateAlgorithms: the verbs, the actions
we performA program manipulates the input (data) to produce the
required output (data)Some Common Data TypesCharacters: Things from
the keyboard'a', 'b', 'Z', '!', '\n'Strings: Sequences of
characters"hi there", "Hello, Bob!", "x", "RESULT"Integers: Whole
numbers, byte, short, int, long-3097, -2, -1, 0, 1, 10,
10340Floating Point Numbers: float, double (have decimals)1.0,
3.14, .333, 100000.0000001Booleans: Truth values for teststrue,
falseNothing: The empty type with no valuevoidASCIIEvery character
has a valueWe store the value, not the characterWe can treat
characters as numbers as a consequenceThe values assigned are based
on the ASCII encoding0-127: Basic ASCII128-255: Extended
ASCII256-65535: Unicode (subsumes ASCII)
Escaped CharactersSometimes we want to remove or add meaning to
characters in a string (Figure 2.6)Can also use this notation to
represent characters from the ASCII tableTo do this we use the
escape character '\' to escape the normal meaning of the next
character\" double quote, don't end the string\' single quote\\ -
just a backslash, not an escape\n newline (go to beginning of next
line)\t tab, expanded using system default\r carriage return (same
as newline ... maybe)IntegersThere are four kinds of integersThe
main difference is the minimum and maximum valuesbyte: -128 to
127short: -32 768 to 32 767int: -2 147 483 648 to 2 147 483
647long: -9 223 372 036 854 775 808 to 9 223 372 036 854 775
807Difference is caused by the amount of memory used to store each
onebyte = 1 byte, short = 2 bytes int = 4 bytes long = 8
bytesVariablesint i;Defines a section of memory large enough to
hold an integer and names that area of memory "i", the memory
contains a random value from whatever it was used for previouslyi =
5;Stores the value 5 in the area or memory named "i"int i = 5;
Combines 1. and 2.A variable holds one, and only one, thingA
variable always has a value ... if you put nothing there then
assume it has a random value
VariablesVariables describe memory locationsValues are stored in
those locationsIdentifiers name locations
int x = 13; location x 13
Right Hand Side (of =): Use the value stored in the location
(used also when no = in expression)Left Hand Side (of =): Use the
location to store the valueOperatorsStandard math: +, -, *,
/Modulus (Remainder): %Assignment to a variable name uses =Can
change the type of something using a castint x = 1;float y =
(float) x;+ is also string concatenatione.g., "Hi " + "there"
creates "Hi there"
See: TextFig 3.9
Delimiters" "A string (sequence of zero or more characters)'a'A
character (a single character, never empty){ }A block (sequence of
zero or more statements)/* */A multi-line comment[ ]An array index(
)A math expressionA test in a loop or conditionalThe arguments of a
method callThe parameters in a method declarationprintfAn
alternative to print or printlnVery powerful and flexiblee.g.,
System.out.printf("An integer: %d", i);Format:
System.out.printf(format-string, values...);The format-string is
printed and every specifier (things that begin with a %) is
replaced with one of the valuesThere must be the same number of
values as specifiersIt was originally in the C programming language
and was added to Java because a lot of C programmers wanted it!
Described on page 101 102
Format Specifiers%c a character%s a string%d an integer%f a
floating point numberWe can modify the values to have a minimum and
a maximum size, left or right justify numbers, pad with
leading/trailing zeros, create columns, etc.E.g., %5d an integer
with 5 digits (spaces added if needed)See:
http://docs.oracle.com/javase/7/docs/api/java/util/Formatter.html#syntaxprintfprintf
(format-string, ... values ...)There must be one value for every
specifier in the format stringformat specifiers begin with a % and
are placed in the format stringE.g. printf("Hello %s!", name);In
this example %s means, put a string here, and name is used to
provide the stringSame as print("Hello " + name + "!");There might
not be any values!E.g., printf("Hello!"); is the same as
print("Hello!");
ExamplesSystem.out.printf ("%d * %d = %d\n", 3, 4,
3*4);System.out.println(3 + " * " + 4 + " = " +
(3*4));System.out.print (3 + " * " + 4 + " = " + (3*4) + "\n");
3 * 4 = 12
System.out.printf ("%s\n%s\n", "Tami",
"Meredith");System.out.println("Tami\nMeredith");System.out.print
("Tami\nMeredith\n");
Tami Meredith
StringsStrings are a special data type (Strings are actually
objects)Ordered and numbered sequences of charactersIndexed from
0Delimited by double quotesE.g., "Hello World!", "", "tami"Large
library of String manipulation methods existsString MethodsSee
Figure 2.5 in the text (page 86)replace(c1,c2) and replace(ss1,ss2)
replace all occurances of c1/ss1 with c2/ss2length() returns the
length of a string (as an integer)indexOf(string2) returns the
index of string2 in string or -1 if string2 is contained in
stringequals(string2) returns TRUE if string equals string2
otherwise it returns FALSEString sentence = "Hello programming
class";int len = sentence.length();boolean same =
sentence.equals("Good bye!");
ExerciseWrite a program that has a single String variable
containing your name as 2 or more wordse.g., String name = "Tami
Michelle Meredith";The program will tell you how many words your
name had. The program must still work correctly if someone changes
the name to have a different number of words.e.g., Tami Michelle
Meredith has 3 names.
Solutionpublic class howMany {
public static void main (String[] args) {
String name = "Tami Michelle Meredith"; String spaceless =
name.replace(" ", ""); int num = name.length() spaceless.length() +
1;
System.out.println(name + " has " + num + " names.");
} // end main()
} // end class howManyControl is Power!Control flow is actually
very simple:Everything is sequential, unless ...Something is
optionalConditional Statements, i.e,. ifSomething is
repeatedLooping Statements, i.e., do, for, whileSomething complex
is broken into simpler partsMethods (and classes, objects)Programs
in JavaPrograms are structured hierarchically:Programs have 1 or
more classesFiles are named after the classes they containClasses
contain 1 or more methodsThe class that is used to start execution
must contain a method named mainMethods perform 1 or more
actionsActions are performed by statements
About Statements ...Statements are like sentences in a
programming languageStatements usually end with a ";"
(semi-colon)Statements are performed sequentially, one after the
other (generally left to right, top to bottom)For example: x = x +
1;y = 2 * x;System.out.println("Y is " + y); StatementsExpressions
and assignmentse.g., x = 3 * y;Conditional statements to make
choicese.g., if (x == 0) System.exit(0);Loops to repeat thingse.g.,
while (i > 0) System.out.println(i--);Blocks to group statements
into a single statemente.g., { statement1; statement2; statement3;
... }BlocksStatements can be grouped into a blockA block is treated
like a single statement and can be used where a single statement is
expectedBlocks are formed by surrounding a group of statements with
curly braces, "{" and "}"For example: { y = x * 2;
System.out.print("Two times " + x + " is " + y);}
Conditional StatementsConditionals make a choice of whether a
statement should be executed:Syntax: if (test) statementWhen test
evaluates to true, statement is executedstatement is singular, a
block must be used to do more than one thing when test is
trueAlternate Syntax:if (test) statement1 else statement2If test is
equal to true then do statement1If test is equal to false then do
statement2Note that there is no ";" at the end of the
conditionalConditional Expressionsif (sex == 'f')
System.out.printf("female");else System.out.printf("male");
>
System.out.printf("%smale", (sex=='f') ? "fe" : "");
Format:(test) ? use-if-true : use-if-false
LoopsExecutes a statement more than onceSyntax:while (test)
statementEvaluate testIf test is equal to true, do step 3,
otherwise donePerform statement then go back to 1Note that
statement is singular and that the loop does not end with a ";"
(but statement does)
Example // Code fragment, counts from 0 to // the value "stop"
input by the user
int count = 0;int stop = user.nextInt();
while (count
