4. More Control Structures and Types

4.1 Logical (Conditional) AND, OR, and NOT

4.2 Nested Ifs and the Switch Statement

4.3 The For and Do-While Loops

4.4 Additional Primitive Types

4.5 Using the Math Library

4.6 Solving Problems with Java: An Iterative

Development Cycle

Objectives

• Learn useful selection and repetition statement

• Use primitive types and operators

• Use the Math library

• Build software using an iterative development cycle

Logical Operators

• Boolean expressions can use logical (conditional) ! Logical NOT

&& Logical AND

|| Logical OR

• They all take boolean operands and produce boolean results

• Logical NOT (Conditional Complement) is a unary operator (one operand), but the other two are binary operators (two operands)

Logical Operators

• Conditions in selection statements and loops can use logical operators to form complex expressions

if (b >= a && c >= a)

min = a;

if (a >= b && c >= b)

min = b;

if (a >= c && b >= c)

min = c;

• Logical operators have precedence relationship between themselves and other operators

Symbol Meaning Example

&& conditional AND (age > 20) && (age < 35)

|| conditional OR (height > 78.5) || (weight > 300)

Figure 4.2 Conditional Operators

age age > 20 age < 35 age > 20 && age < 35

10 false true false

25 true true true

40 true false false

Figure 4.3 Evaluating an example of a conditional AND expression

A B A && B

true true true

true false false

false (don't care) false

Figure 4.4 Evaluating a conditional AND expression

height weight height > 78.5 weight > 300 (height>78.5) || (weight>300)

62 125 false false false

80 250 true false true

72 310 false true true

80 325 true true true

Figure 4.5 Evaluating an example of a conditional OR expression

A B A || B

true (don't care) true

false true true

false false false

Figure 4.6 Evaluating a condition OR expression

A !A

true false

false true

Figure 4.7 Evaluating a logical complement expression

Figure 4.8 Operator precedence*

Highest

NOT! !

multiplicative * / %

additive + -

relational < > <= >=

equality == !=

conditional AND &&

conditional OR ||

assignment = += -= *= /= %=

Lowest

if (score >= 60 && score < 80)

System.out.println("Score " + score + " receives a C");

else

System.out.println("Score " + score + " receives a B or an A");

Figure 4.9 If-else statement to choose between two alternatives

Nested If Statements• The if-true-statement and if-false-statement of an

if statement could be another if statement• These are called nested if statements

if (a >= b) if (b >= c) min = c; else min = b;

else if (a >= c) min = c; else min = a;

• An else clause is matched to the last unmatched if (no matter what the indentation implies)

Figure 4.10 Nested if-else statement to choose among three alternatives

if (score >= 60 && score < 80) System.out.println("Score " + score + " receives a C");else if (score >=80 && score < 90) System.out.println("Score " + score + " receives a B");else System.out.println("Score " + score + " receives an A"); 

Figure 4.11 Improved version of Figure 4.10

if (score >= 60 && score < 80) System.out.println("Score " + score + " receives a C");else if (score >=80 && score < 90) System.out.println("Score " + score + " receives a B");else if (score >= 90 && score <= 100) System.out.println("Score " + score + " receives an A");

Figure 4.12 Flow chart for nested if-else statements

Last?

Last false code

...

Last true codeTrue

False

False

Test1?

Test2?

Test1 true code

Test2 true code

True

True

False

False

Figure 4.13 Incorrect attempt to pair an else with an if

if (score >= 60) if (score >= 80) System.out.println("You got a B or an A");else System.out.println("You got a D or an F"); // Wrong pairing

Figure 4.14 Corrected pairing of else and if

if (score >= 60) if (score >= 80) System.out.println("You got a B or an A"); else System.out.println("You got a C"); // Correct pairing

Figure 4.15 Figure 4.13 rewritten as an if-else with nested if

if (score >= 60) { if (score >= 80) System.out.println("You got a B or an A");}Else // Paired to first 'if' System.out.println("You got a D or an F");

The Switch Statement

• The switch statement provides another means to decide which statement to execute next

• The switch statement evaluates an expression, then attempts to match the result to one of several possible cases

• Each case contains a value and a list of statements• The flow of control transfers to statement list

associated with the first value that matches

The Switch Statement

• A switch statement can have an optional default case which has no associated value

• If the default case is present, control will transfer to it if no other case value matches

• The default case can be positioned anywhere in the switch, it is usually placed at the end

• If there is no default case, and no other value matches, control falls through to the next statement after the switch

The Switch Statement

• Often a break statement is used as the last statement in each case’s statement list

• A break statement causes control to transfer to the end of the switch statement

• If a break statement is not used, the flow of control will continue into the next case

• The expression of a switch statement must result in an integral data type, like an integer or character

• You cannot perform relational checks with a switch staement

Figure 4.16 An example of a switch statement

switch(mark) { case 0: case 1: case 2: case 3: case 4: System.out.println("F"); break; case 5: System.out.println("D"); break; case 6: case 7: System.out.println("C"); break; case 8: System.out.println("B"); break; case 9: case10: System.out.println("A"); break; default:System.out.println("Incorrect score");}

The For Statement

• The for statement has the following syntax:for ( initialization ; condition ; increment )

statement ;

• The initialization is executed once before the loop begins

• The statement is executed until the condition becomes false

• The increment portion is executed at the end of each iteration

The For Statement• The for statement is equivalent to the following

while loop structureinitialization ;while ( condition ){ statement ; increment ;}

• Like a while loop, the condition of a for loop is tested prior to executing the loop body

• Therefore, the body of a for loop can be executed zero or more times

Figure 4.17 A for statement for the sum 1+2+3+4

int sum = 0;for (int i = 1; i <= 4; i++) sum += i;

initialize i = 1

test 1 <= 4 is true

execute body sum += 1 (result: sum = 0 + 1 = 1)

update i++ (result: i = 2)

test 2 <= 4 is true

execute body sum += 2 (result: sum = 1 + 2 = 3)

update i++ (result: i = 3)

test 3 <= 4 is true

execute body sum += 3 (result: sum = 3 + 3 = 6)

update i++ (result: i + 4)

test 4 <= 4 is true

execute body sum += 4 (result: sum = 6 + 4 = 10)

update i++ (result: i = 5)

test 5 <= 4 is false

Figure 4.18 Trace of execution of the for loop of Figure 4.17

Figure 4.19 A for statement for the sum 1+3+5+7+9

int sum = 0;for (int i = 1; i < 10; i += 2) sum += i;

Figure 4.20 A for statement for the sum 4+3+2+1

int sum = 0;for (int i = 4; i >= l; i--) sum += i;

Figure 4.21 Declaring an index variable before the for loop

int i; // declare loop indexint sum = 0;for (i = 4; i >= 1; i--) // initialize loop index sum += i;...i += 17; // use variable i

Examples• TwelveDays.java (extra)

• Diamond.java (extra)

• Growth.java• Mortgage.java (extra)

The StringTokenizer Class• StringTokenizer(String str)

Constructor. Creates a new StringTokenizer object to parse str based on white space

• StringTokenizer(String str, String delimiter)Constructor. Creates a new StringTokenizer object to parse str based

on specified set of delimiteds

• int countTokens()Returns the number of token still left to be processed in the string

• boolean hasMoreTokens()Returns true if there are tokens still left to be processed in the string

• String nextToken()Returns the next token in the string

Figure 4.22 Syntax for the do-while statement

do statementwhile (condition) ;

Do-while Statement• A do-while statement checks the condition after

executing the loop body• The loop body of a do-while statement is executed

at least once• Do-while statements are suitable for writing loops

that are executed at least once

• DoGrowth.java• Babylonian.java (extra)

Figure 4.23 Pseudocode for example 4.5 enhancement

do { Compute balance as in Example 4.5 Ask the user -- Repeat or Quit?} while (User chooses to repeat);

The char Type• Java uses Unicode charater set (16 bits)• ASCII, American Standard Code for Information

Interchange, is a seven-bit code used by other language like C and C++

• ASCII is a subset of Unicode• Keyword char to denote character type• Character constants are quoted in single quotes,

e.g. ‘A’• Ascii.java

Escape Sequence• Escape sequence: preceding certain character with

the escape character \ for special meaning• The newline, '\n', positions the next output at

the start of the next line• The return, '\r', positions the next output at the

start of the curent line• The backspace, '\b', positions the next output

one character to the left• The tab, '\t', position the next output at the next

tab position

Escape Sequence• The escape needs to be "escaped" when quoted

like '\\' and "\\"• The single quote character must be "escaped" in

single quotes like '\''• The double quote must be "escaped" in double

quotes like ”\”This is a quote\”"• Special.java

\\backlash

 

Special

Character

Meaning

\n newline, move to the start of the next line

\t tab

\b backspace

\r return, move to the start of the current line

\" double quote

\n newline, move to the start of the next line

Figure 4.24 Escape sequences for special characters

The byte, short, and long Types• byte: one byte = 8 bits, range from -128 to 127

• short: two bytes = 16 bits– range from -32,768 to 32,767

• int: four bytes = 32 bits– range from -2,147,483,648 to 2,147,483,647

• long: eight bytes = 64 bits– range 9,223,372,036,854,808 to 9,223,372,036,854,807

• int is the default for integer constant• Integer constants can be made long by adding the

suffix l or L

The float Type• float: four bytes = 32 bits

– Exponent can range from -45 to 48– Min ~ -3.4E+38 with seven significant digits– Max ~ 3.4E+38 with seven significant digits

• double: eight bytes = 64 bits– Exponent can range from -324 to 308– Min ~ -1.7E+308 with 16 significant digits– Max ~ 1.7E+308 with 16 significant digits

• double is the default for real constants• Make a number float by adding an f or F suffix

float good = 4.25f; // validfloat ok = (float)4.25; // validfloat bad = 4.25; // invalid

The Math Class• In java.lang package• Two static constants: E (base of natural log) and

PI (ratio of circumference of a circle to its diameter)

• General functionsabs - absolute value

ceil - ceiling, smallest integer >= argument

floor - flooring, greatest integer <= argument

round - rounding, integer closest to argument

max - maximum of the two arguments

min - minimum of the two arguments

The Math Class• Simple mathematical operations

sqrt(double a) - Return the square root of the argument

pow(double a, double b) - Returns of value of the first argument raised to the power of the second argument

log(double a) - Returns the natural logarithm (base e) of a double value

exp(double a) - Returns the exponential number e (i.e., 2.718...) raised to the power of a double value

• Random numberrandom() - Returns a double value with a positive sign,

greater than or equal to 0.0 and less than 1.0

The Math Class• Trigonometric functions

sin, cos, tan - sine, cosine, and tangent

asin, acos, atan- arc-sine, arc-cosine, and arc-tangent

atan2(double a, double b) - Returns the theta component in the polar coordinates (r, theta) corresponding to the point (b, a) in Cartesian coordinates

• Degree/Radian conversiontoDegrees(double angrad) - Converts an angle in

radians to the equivalent angle measured in degrees

toRadians(double angdeg) - Converts an angle in degrees to the equivalent angle measured in radians

The Math Class• Library.java

• Toss.java

• CoinToss.java

Figure 4.25 Size of the reward given each day

Reward

11

2

4

8

12 16

16

8

4

2

Days

(grains of rice)

Figure 4.26 Using random numbers to represent heads and tails

0.0 0.5 1.0

HHHHHHHHHHHHHHHHHTTTTTTTTTTTTTTTTTT

Heads Tails

Iterative Development Cycle

• First iteration - CovertMenu.java (with stubs for methods)

• Second iteration - CovertFromMetric.java (implement MetricToEnglish())

• Third iteration - Convert.java (implement EnglishToMetric())

Figure 4.27 Iterative problem-solving process

Formulate the problem;do { Develop pseudocode; Implement pseudocode in Java program; Test program;while (More subproblems to refine);

Figure 4.28 Top-level Pseudocode

do [ Display the menu; Get the user's choice; Execute the user's choice;} while (user does not choose to quit);

Figure 4.29 Pattern for a menu-driven application

do { System.out.println(); System.out.println("Choose from the following list"); System.out.println("1. Convert from meters to yds,ft,in"); System.out,println("2. Convert from yds,ft,in to meters"); System.out.println("3. Quit"); int choice = Io.readInt("Enter your choice, 1, 2 or 3"); switch (choice) { case 1: MetricToEnglish(); break; case 2: EnglishToMetric(); break; case 3: System.out.println("Bye, Have a nice day"); }} while (choice != 3);

Figure 4.30 Pseudocode for the MetricToEnglish method

Input the number of meters, x, to convert;Convert x meters to y yards;Separate y into yInteger yards and yFraction yards;Convert yFraction yards to f feet.Separate f into fInteger feet and fFraction feet.Convert fFraction feet to i inches.Display the output.

Figure 4.31 Refinement:Display the output

if (yInteger > 0) if (yInteger <= 1) Display yInteger yard; else Display yInteger yards;if (fInteger > 0) if (fInteger <= 1) Display fInteger foot; else Display fInteger feet;if (i >0) if (i <= 1) Display i inch; else Display i inches;if (yInteger == 0 && fInteger == 0 && i == 0) Display 0 yards;

Figure 4.32 Pseudocode for the EnglishToMetric method

Input yards, feet, and inches to convert;Convert to inches;Convert inches to meters;Output the result;