Chapter 3 SelectionsLiang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights re...
MotivationsIf you assigned a negative value for radius inListing 2.1, ComputeArea.java, the program wouldprint an invalid ...
Objectives   To declare boolean variables and write Boolean expressions using comparison operators (§3.2).   To implemen...
The boolean Type and OperatorsOften in a program you need to compare twovalues, such as whether i is greater than j. Javap...
Comparison OperatorsJava       Mathematics                  Name                                            Example       ...
Problem: A Simple Math Learning ToolThis example creates a program to let a first graderpractice additions. The program ra...
One-way if Statements                                                                 if (radius >= 0) {                  ...
Noteif i > 0 {                                                        if (i > 0) {  System.out.println("i is positive");  ...
Simple if DemoWrite a program that prompts the user to enter an integer. If thenumber is a multiple of 5, print HiFive. If...
Problem: Guessing BirthdayThe program can guess your birth date. Runto see how it works.                                  ...
Mathematics Basis for the Game19 is 10011 in binary. 7 is 111 in binary. 23 is 11101 in binary                            ...
The Two-way if Statementif (boolean-expression) {  statement(s)-for-the-true-case;}else {  statement(s)-for-the-false-case...
if-else Exampleif (radius >= 0) {  area = radius * radius * 3.14159; System.out.println("The area for the “   + “circle of...
Multiple Alternative if Statementsif (score >= 90.0)                                                        if (score >= 9...
Multi-Way if-else Statements               falsescore >= 90                                                  falsetrue    ...
animation                    Trace if-else statement     Suppose score is 70.0                             The condition i...
animation                    Trace if-else statement     Suppose score is 70.0                             The condition i...
animation                    Trace if-else statement     Suppose score is 70.0                              The condition ...
animation                    Trace if-else statement     Suppose score is 70.0                                       grade...
animation                    Trace if-else statement     Suppose score is 70.0                              Exit the if st...
NoteThe else clause matches the most recent if clause in thesame block.int i = 1;                                         ...
Note, cont.Nothing is printed from the preceding statement. Toforce the else clause to match the first if clause, you must...
Common ErrorsAdding a semicolon at the end of an if clause is a commonmistake.if (radius >= 0);            Wrong{  area = ...
TIPif (number % 2 == 0)                           Equivalent  even = true;                                                ...
CAUTIONif (even == true)                                 Equivalent              if (even)  System.out.println(           ...
Problem: An Improved Math Learning ToolThis example creates a program to teach afirst grade child how to learn subtraction...
Problem: Body Mass IndexBody Mass Index (BMI) is a measure of health onweight. It can be calculated by taking your weighti...
Problem: Computing TaxesThe US federal personal income tax is calculatedbased on the filing status and taxable income.Ther...
Problem: Computing Taxes, cont.if (status == 0) {  // Compute tax for single filers}else if (status == 1) {  // Compute ta...
Logical OperatorsOperator Name!                   not&&                  and||                  or^                   excl...
Truth Table for Operator !p       !p                                             Example (assume age = 24, gender = M)true...
Truth Table for Operator &&p1       p2              p1 && p2                          Example (assume age = 24, gender = F...
Truth Table for Operator ||p1      p2            p1 || p2                          Example (assume age = 24, gender = F)fa...
Truth Table for Operator ^p1      p2               p1 ^ p2                            Example (assume age = 24, gender = F...
ExamplesHere is a program that checks whether a number is divisible by 2and 3, whether a number is divisible by 2 or 3, an...
ExamplesSystem.out.println("Is " + number + " divisible by 2 and 3? " + ((number % 2 == 0) && (number % 3 == 0)));System.o...
CompanionWebsite                    The & and | OperatorsSupplement III.B, “The & and | Operators”            Liang, Intro...
CompanionWebsite                    The & and | Operators    If x is 1, what is x after this      expression?    (x > 1) &...
Problem: Determining Leap Year?This program first prompts the user to enter a year asan int value and checks if it is a le...
Problem: LotteryWrite a program that randomly generates a lottery of a two-digit number, prompts the user to enter a two-d...
switch Statementsswitch (status) {  case 0: compute taxes for single filers;        break;  case 1: compute taxes for marr...
switch Statement Flow Chart  status is 0                Compute tax for single filers                                     ...
switch Statement RulesThe switch-expressionmust yield a value of char,                              switch (switch-express...
switch Statement RulesThe keyword break is optional,                                  switch (switch-expression) {but it s...
animation                       Trace switch statement        Suppose ch is a: switch       (ch)           {   case       ...
animation                   Trace switch statement                                     ch is a: switch     (ch)         { ...
animation                   Trace switch statement                              Execute this line switch     (ch)         ...
animation                   Trace switch statement                              Execute this line switch     (ch)         ...
animation                   Trace switch statement                              Execute this line switch     (ch)         ...
animation                   Trace switch statement                         Execute next statement switch     (ch)         ...
animation                       Trace switch statement        Suppose ch is a: switch (ch) {   case a: System.out.println(...
animation                   Trace switch statement                                      ch is a: switch (ch) {   case a: S...
animation                   Trace switch statement                               Execute this line switch (ch) {   case a:...
animation                   Trace switch statement                               Execute this line switch (ch) {   case a:...
animation                   Trace switch statement                          Execute next statement switch (ch) {   case a:...
Problem: Chinese ZodiacWrite a program that prompts the user to enter a yearand displays the animal for the year.         ...
Conditional Operatorif (x > 0)  y=1else  y = -1;is equivalent toy = (x > 0) ? 1 : -1;(boolean-expression) ? expression1 : ...
Conditional Operatorif (num % 2 == 0)  System.out.println(num + “is even”);else  System.out.println(num + “is odd”);System...
Conditional Operator, cont.(boolean-expression) ? exp1 : exp2      Liang, Introduction to Java Programming, Ninth Edition,...
Formatting OutputUse the printf statement.   System.out.printf(format, items);Where format is a string that may consist of...
Frequently-Used SpecifiersSpecifier Output                                                                                ...
Operator Precedence   var++, var--   +, - (Unary plus and minus), ++var,--var   (type) Casting   ! (Not)   *, /, % (M...
Operator Precedence and AssociativityThe expression in the parentheses is evaluated first.(Parentheses can be nested, in w...
Operator AssociativityWhen two operators with the same precedenceare evaluated, the associativity of the operatorsdetermin...
ExampleApplying the operator precedence and associativity rule,the expression 3 + 4 * 4 > 5 * (4 + 3) - 1 is evaluated asf...
CompanionWebsite            Operand Evaluation Order     Supplement III.A, “Advanced discussions on     how an expression ...
(GUI) Confirmation Dialogsint option = JOptionPane.showConfirmDialog    (null, "Continue");        Liang, Introduction to ...
Problem: Guessing Birth DateThe program can guess your birth date. Runto see how it works.                                ...
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JavaYDL3

  1. 1. Chapter 3 SelectionsLiang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 1
  2. 2. MotivationsIf you assigned a negative value for radius inListing 2.1, ComputeArea.java, the program wouldprint an invalid result. If the radius is negative, youdont want the program to compute the area. Howcan you deal with this situation? Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 2
  3. 3. Objectives To declare boolean variables and write Boolean expressions using comparison operators (§3.2). To implement selection control using one-way if statements (§3.3). To program using one-way if statements (GuessBirthday) (§3.4). To implement selection control using two-way if-else statements (§3.5). To implement selection control using nested if and multi-way if statements (§3.6). To avoid common errors in if statements (§3.7). To generate random numbers using the Math.random() method (§3.8). To program using selection statements for a variety of examples (SubtractionQuiz, BMI, ComputeTax) (§§3.8–3.10). To combine conditions using logical operators (&&, ||, and !) (§3.11). To program using selection statements with combined conditions (LeapYear, Lottery) (§§3.12– 3.13). To implement selection control using switch statements (§3.14). To write expressions using the conditional operator (§3.15). To format output using the System.out.printf method (§3.16). To examine the rules governing operator precedence and associativity (§3.17). To get user confirmation using confirmation dialogs (§3.18). To apply common techniques to debug errors (§3.19). Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 3
  4. 4. The boolean Type and OperatorsOften in a program you need to compare twovalues, such as whether i is greater than j. Javaprovides six comparison operators (also knownas relational operators) that can be used tocompare two values. The result of thecomparison is a Boolean value: true or false.boolean b = (1 > 2); Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 4
  5. 5. Comparison OperatorsJava Mathematics Name Example ResultOperator Symbol (radius is 5)< < less than radius < 0 false<= ≤ less than or equal to radius <= 0 false> > greater than radius > 0 true>= ≥ greater than or equal to radius >= 0 true== = equal to radius == 0 false!= ≠ not equal to radius != 0 true Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 5
  6. 6. Problem: A Simple Math Learning ToolThis example creates a program to let a first graderpractice additions. The program randomlygenerates two single-digit integers number1 andnumber2 and displays a question such as “What is7 + 9?” to the student. After the student types theanswer, the program displays a message to indicatewhether the answer is true or false. AdditionQuiz Run Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 6
  7. 7. One-way if Statements if (radius >= 0) { area = radius * radius * PI;if (boolean-expression) { System.out.println("The area" statement(s); + " for the circle of radius "} + radius + " is " + area); } false false Boolean (radius >= 0) Expression true true Statement(s) area = radius * radius * PI; System.out.println("The area for the circle of " + "radius " + radius + " is " + area); (A) (B) Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 7
  8. 8. Noteif i > 0 { if (i > 0) { System.out.println("i is positive"); System.out.println("i is positive");} } (a) Wrong (b) Correctif (i > 0) { if (i > 0) System.out.println("i is positive"); Equivalent System.out.println("i is positive");} (a) (b) Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 8
  9. 9. Simple if DemoWrite a program that prompts the user to enter an integer. If thenumber is a multiple of 5, print HiFive. If the number is divisibleby 2, print HiEven. SimpleIfDemo Run Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 9
  10. 10. Problem: Guessing BirthdayThe program can guess your birth date. Runto see how it works. = 19 + 1 3 5 7 2 3 6 7 4 5 6 7 8 9 10 11 16 17 18 19 9 11 13 15 10 11 14 15 12 13 14 15 12 13 14 15 20 21 22 2317 19 21 23 18 19 22 23 20 21 22 23 24 25 26 27 24 25 26 2725 27 29 31 26 27 30 31 28 29 30 31 28 29 30 31 28 29 30 31 Set1 Set2 Set3 Set4 Set5 GuessBirthday Run Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 10
  11. 11. Mathematics Basis for the Game19 is 10011 in binary. 7 is 111 in binary. 23 is 11101 in binary 10000 10000 00110 1000 10 10 100 + 1 + 1 + 1 10011 00111 11101 19 7 23 = 19 + 1 3 5 7 2 3 6 7 4 5 6 7 8 9 10 11 16 17 18 19 9 11 13 15 10 11 14 15 12 13 14 15 12 13 14 15 20 21 22 2317 19 21 23 18 19 22 23 20 21 22 23 24 25 26 27 24 25 26 2725 27 29 31 26 27 30 31 28 29 30 31 28 29 30 31 28 29 30 31 Set1 Set2 Set3 Set4 Set5 Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 11
  12. 12. The Two-way if Statementif (boolean-expression) { statement(s)-for-the-true-case;}else { statement(s)-for-the-false-case;} true false Boolean Expression Statement(s) for the true case Statement(s) for the false case Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 12
  13. 13. if-else Exampleif (radius >= 0) { area = radius * radius * 3.14159; System.out.println("The area for the “ + “circle of radius " + radius + " is " + area);}else { System.out.println("Negative input");} Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 13
  14. 14. Multiple Alternative if Statementsif (score >= 90.0) if (score >= 90.0) grade = A; grade = A;else else if (score >= 80.0) if (score >= 80.0) Equivalent grade = B; grade = B; else if (score >= 70.0) else grade = C; if (score >= 70.0) else if (score >= 60.0) grade = C; grade = D; else else if (score >= 60.0) grade = F; grade = D; else grade = F; Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 14
  15. 15. Multi-Way if-else Statements falsescore >= 90 falsetrue score >= 80 false grade = A true score >= 70 false grade = B rue score >= 60 grade = C true grade = D grade = F Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 15
  16. 16. animation Trace if-else statement Suppose score is 70.0 The condition is false if (score >= 90.0) grade = A; else if (score >= 80.0) grade = B; else if (score >= 70.0) grade = C; else if (score >= 60.0) grade = D; else grade = F; Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 16
  17. 17. animation Trace if-else statement Suppose score is 70.0 The condition is false if (score >= 90.0) grade = A; else if (score >= 80.0) grade = B; else if (score >= 70.0) grade = C; else if (score >= 60.0) grade = D; else grade = F; Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 17
  18. 18. animation Trace if-else statement Suppose score is 70.0 The condition is true if (score >= 90.0) grade = A; else if (score >= 80.0) grade = B; else if (score >= 70.0) grade = C; else if (score >= 60.0) grade = D; else grade = F; Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 18
  19. 19. animation Trace if-else statement Suppose score is 70.0 grade is C if (score >= 90.0) grade = A; else if (score >= 80.0) grade = B; else if (score >= 70.0) grade = C; else if (score >= 60.0) grade = D; else grade = F; Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 19
  20. 20. animation Trace if-else statement Suppose score is 70.0 Exit the if statement if (score >= 90.0) grade = A; else if (score >= 80.0) grade = B; else if (score >= 70.0) grade = C; else if (score >= 60.0) grade = D; else grade = F; Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 20
  21. 21. NoteThe else clause matches the most recent if clause in thesame block.int i = 1; int i = 1;int j = 2; int j = 2;int k = 3; int k = 3; Equivalentif (i > j) if (i > j) if (i > k) if (i > k) System.out.println("A"); System.out.println("A");else else System.out.println("B"); System.out.println("B"); (a) (b) Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 21
  22. 22. Note, cont.Nothing is printed from the preceding statement. Toforce the else clause to match the first if clause, you mustadd a pair of braces: int i = 1; int j = 2; int k = 3; if (i > j) { if (i > k) System.out.println("A"); } else System.out.println("B");This statement prints B. Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 22
  23. 23. Common ErrorsAdding a semicolon at the end of an if clause is a commonmistake.if (radius >= 0); Wrong{ area = radius*radius*PI; System.out.println( "The area for the circle of radius " + radius + " is " + area);}This mistake is hard to find, because it is not a compilation error ora runtime error, it is a logic error.This error often occurs when you use the next-line block style. Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 23
  24. 24. TIPif (number % 2 == 0) Equivalent even = true; boolean evenelse = number % 2 == 0; even = false; (a) (b) Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 24
  25. 25. CAUTIONif (even == true) Equivalent if (even) System.out.println( System.out.println( "It is even."); "It is even."); (a) (b) Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 25
  26. 26. Problem: An Improved Math Learning ToolThis example creates a program to teach afirst grade child how to learn subtractions.The program randomly generates two single-digit integers number1 and number2 withnumber1 > number2 and displays a questionsuch as “What is 9 – 2?” to the student. Afterthe student types the answer in the inputdialog box, the program displays a messagedialog box to indicate whether the answer iscorrect. SubtractionQuiz Run Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 26
  27. 27. Problem: Body Mass IndexBody Mass Index (BMI) is a measure of health onweight. It can be calculated by taking your weightin kilograms and dividing by the square of yourheight in meters. The interpretation of BMI forpeople 16 years or older is as follows: BMI Interpretation Below 18.5 Underweight 18.5-24.9 Normal 25.0-29.9 Overweight Above 30.0 Obese ComputeAndInterpretBMI Run Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 27
  28. 28. Problem: Computing TaxesThe US federal personal income tax is calculatedbased on the filing status and taxable income.There are four filing statuses: single filers, marriedfiling jointly, married filing separately, and head ofhousehold. The tax rates for 2009 are shown below. Married Filing Marginal Married Filing Single Jointly or Qualifying Head of Household Tax Rate Separately Widow(er) 10% $0 – $8,350 $0 – $16,700 $0 – $8,350 $0 – $11,950 15% $8,351– $33,950 $16,701 – $67,900 $8,351 – $33,950 $11,951 – $45,500 25% $33,951 – $82,250 $67,901 – $137,050 $33,951 – $68,525 $45,501 – $117,450 28% $82,251 – $171,550 $137,051 – $208,850 $68,525 – $104,425 $117,451 – $190,200 33% $171,551 – $372,950 $208,851 – $372,950 $104,426 – $186,475 $190,201 - $372,950 35% $372,951+ $372,951+ $186,476+ $372,951+ Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 28
  29. 29. Problem: Computing Taxes, cont.if (status == 0) { // Compute tax for single filers}else if (status == 1) { // Compute tax for married file jointly // or qualifying widow(er)}else if (status == 2) { // Compute tax for married file separately}else if (status == 3) { // Compute tax for head of household}else { // Display wrong status} ComputeTax Run Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 29
  30. 30. Logical OperatorsOperator Name! not&& and|| or^ exclusive or Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 30
  31. 31. Truth Table for Operator !p !p Example (assume age = 24, gender = M)true false !(age > 18) is false, because (age > 18) is true.false true !(gender != M) is true, because (grade != M) is false. Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 31
  32. 32. Truth Table for Operator &&p1 p2 p1 && p2 Example (assume age = 24, gender = F)false false false (age > 18) && (gender == F) is true, because (agefalse true false > 18) and (gender == F) are both true.true false false (age > 18) && (gender != F) is false, because (gender != F) is false.true true true Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 32
  33. 33. Truth Table for Operator ||p1 p2 p1 || p2 Example (assume age = 24, gender = F)false false false (age > 34) || (gender == F) is true, because (genderfalse true true == F) is true.true false true (age > 34) || (gender == M) is false, because (age >true true true 34) and (gender == M) are both false. Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 33
  34. 34. Truth Table for Operator ^p1 p2 p1 ^ p2 Example (assume age = 24, gender = F)false false false (age > 34) ^ (gender == F) is true, because (agefalse true true > 34) is false but (gender == F) is true.true false true (age > 34) || (gender == M) is false, because (age > 34) and (gender == M) are both false.true true false Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 34
  35. 35. ExamplesHere is a program that checks whether a number is divisible by 2and 3, whether a number is divisible by 2 or 3, and whether anumber is divisible by 2 or 3 but not both:TestBooleanOperators Run Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 35
  36. 36. ExamplesSystem.out.println("Is " + number + " divisible by 2 and 3? " + ((number % 2 == 0) && (number % 3 == 0)));System.out.println("Is " + number + " divisible by 2 or 3? " + ((number % 2 == 0) || (number % 3 == 0)));System.out.println("Is " + number + TestBooleanOperators " divisible by 2 or 3, but not both? " + ((number % 2 == 0) ^ (number % 3 == 0))); Run Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 36
  37. 37. CompanionWebsite The & and | OperatorsSupplement III.B, “The & and | Operators” Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 37
  38. 38. CompanionWebsite The & and | Operators If x is 1, what is x after this expression? (x > 1) & (x++ < 10) If x is 1, what is x after this expression? (1 > x) && ( 1 > x++) How about (1 == x) | (10 > x++)? (1 == x) || (10 > x++)? Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 38
  39. 39. Problem: Determining Leap Year?This program first prompts the user to enter a year asan int value and checks if it is a leap year.A year is a leap year if it is divisible by 4 but not by100, or it is divisible by 400.(year % 4 == 0 && year % 100 != 0) || (year % 400== 0) LeapYear Run Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 39
  40. 40. Problem: LotteryWrite a program that randomly generates a lottery of a two-digit number, prompts the user to enter a two-digit number,and determines whether the user wins according to thefollowing rule:• If the user input matches the lottery in exact order, the award is $10,000.• If the user input matches the lottery, the award is $3,000.• If one digit in the user input matches a digit in the lottery, the award is $1,000. Lottery Run Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 40
  41. 41. switch Statementsswitch (status) { case 0: compute taxes for single filers; break; case 1: compute taxes for married file jointly; break; case 2: compute taxes for married file separately; break; case 3: compute taxes for head of household; break; default: System.out.println("Errors: invalid status"); System.exit(1);} Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 41
  42. 42. switch Statement Flow Chart status is 0 Compute tax for single filers break status is 1 Compute tax for married jointly or qualifying widow(er) break status is 2 Compute tax for married filing separately break status is 3 Compute tax for head of household break default Default actions Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 42
  43. 43. switch Statement RulesThe switch-expressionmust yield a value of char, switch (switch-expression) {byte, short, or int type andmust always be enclosed in case value1: statement(s)1;parentheses. break; case value2: statement(s)2;The value1, ..., and valueN must break;have the same data type as the …value of the switch-expression.The resulting statements in the case valueN: statement(s)N;case statement are executed when break;the value in the case statement default: statement(s)-for-default;matches the value of the switch- }expression. Note that value1, ...,and valueN are constantexpressions, meaning that theycannot contain variables in theexpression, such as 1 + x. Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 43
  44. 44. switch Statement RulesThe keyword break is optional, switch (switch-expression) {but it should be used at the end of case value1: statement(s)1;each case in order to terminate theremainder of the switch break;statement. If the break statement case value2: statement(s)2;is not present, the next casestatement will be executed. break; … case valueN: statement(s)N;The default case, which is break;optional, can be used to perform default: statement(s)-for-default;actions when none of thespecified cases matches the }switch-expression. The case statements are executed in sequential order, but the order of the cases (including the default case) does not matter. However, it is good programming style to follow the logical sequence of the cases and place the default case at the end. Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 44
  45. 45. animation Trace switch statement Suppose ch is a: switch (ch) { case a: System.out.println(ch); case b: System.out.println(ch); case c: System.out.println(ch); } Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 45
  46. 46. animation Trace switch statement ch is a: switch (ch) { case a: System.out.println(ch); case b: System.out.println(ch); case c: System.out.println(ch); } Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 46
  47. 47. animation Trace switch statement Execute this line switch (ch) { case a: System.out.println(ch); case b: System.out.println(ch); case c: System.out.println(ch); } Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 47
  48. 48. animation Trace switch statement Execute this line switch (ch) { case a: System.out.println(ch); case b: System.out.println(ch); case c: System.out.println(ch); } Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 48
  49. 49. animation Trace switch statement Execute this line switch (ch) { case a: System.out.println(ch); case b: System.out.println(ch); case c: System.out.println(ch); } Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 49
  50. 50. animation Trace switch statement Execute next statement switch (ch) { case a: System.out.println(ch); case b: System.out.println(ch); case c: System.out.println(ch); } Next statement; Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 50
  51. 51. animation Trace switch statement Suppose ch is a: switch (ch) { case a: System.out.println(ch); break; case b: System.out.println(ch); break; case c: System.out.println(ch); } Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 51
  52. 52. animation Trace switch statement ch is a: switch (ch) { case a: System.out.println(ch); break; case b: System.out.println(ch); break; case c: System.out.println(ch); } Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 52
  53. 53. animation Trace switch statement Execute this line switch (ch) { case a: System.out.println(ch); break; case b: System.out.println(ch); break; case c: System.out.println(ch); } Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 53
  54. 54. animation Trace switch statement Execute this line switch (ch) { case a: System.out.println(ch); break; case b: System.out.println(ch); break; case c: System.out.println(ch); } Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 54
  55. 55. animation Trace switch statement Execute next statement switch (ch) { case a: System.out.println(ch); break; case b: System.out.println(ch); break; case c: System.out.println(ch); } Next statement; Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 55
  56. 56. Problem: Chinese ZodiacWrite a program that prompts the user to enter a yearand displays the animal for the year. pig 0: monkey rat 1: rooster dog ox 2: dog 3: pig rooster tiger 4: rat year % 12 = 5: ox monkey rabbit 6: tiger 7: rabbit 8: dragon sheep dragon 9: snake horse snake 10: horse 11: sheep ChineseZodiac Run Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 56
  57. 57. Conditional Operatorif (x > 0) y=1else y = -1;is equivalent toy = (x > 0) ? 1 : -1;(boolean-expression) ? expression1 : expression2Ternary operatorBinary operatorUnary operator Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 57
  58. 58. Conditional Operatorif (num % 2 == 0) System.out.println(num + “is even”);else System.out.println(num + “is odd”);System.out.println( (num % 2 == 0)? num + “is even” : num + “is odd”); Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 58
  59. 59. Conditional Operator, cont.(boolean-expression) ? exp1 : exp2 Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 59
  60. 60. Formatting OutputUse the printf statement. System.out.printf(format, items);Where format is a string that may consist of substrings andformat specifiers. A format specifier specifies how an itemshould be displayed. An item may be a numeric value,character, boolean value, or a string. Each specifier beginswith a percent sign. Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 60
  61. 61. Frequently-Used SpecifiersSpecifier Output Example%b a boolean value true or false%c a character a%d a decimal integer 200%f a floating-point number 45.460000%e a number in standard scientific notation 4.556000e+01%s a string "Java is cool" int count = 5; items double amount = 45.56; System.out.printf("count is %d and amount is %f", count, amount); display count is 5 and amount is 45.560000 Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 61
  62. 62. Operator Precedence var++, var-- +, - (Unary plus and minus), ++var,--var (type) Casting ! (Not) *, /, % (Multiplication, division, and remainder) +, - (Binary addition and subtraction) <, <=, >, >= (Comparison) ==, !=; (Equality) ^ (Exclusive OR) && (Conditional AND) Short-circuit AND || (Conditional OR) Short-circuit OR =, +=, -=, *=, /=, %= (Assignment operator) Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 62
  63. 63. Operator Precedence and AssociativityThe expression in the parentheses is evaluated first.(Parentheses can be nested, in which case the expressionin the inner parentheses is executed first.) Whenevaluating an expression without parentheses, theoperators are applied according to the precedence rule andthe associativity rule.If operators with the same precedence are next to eachother, their associativity determines the order ofevaluation. All binary operators except assignmentoperators are left-associative. Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 63
  64. 64. Operator AssociativityWhen two operators with the same precedenceare evaluated, the associativity of the operatorsdetermines the order of evaluation. All binaryoperators except assignment operators are left-associative.a – b + c – d is equivalent to ((a – b) + c) – dAssignment operators are right-associative.Therefore, the expressiona = b += c = 5 is equivalent to a = (b += (c = 5)) Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 64
  65. 65. ExampleApplying the operator precedence and associativity rule,the expression 3 + 4 * 4 > 5 * (4 + 3) - 1 is evaluated asfollows: 3 + 4 * 4 > 5 * (4 + 3) - 1 (1) inside parentheses first 3 + 4 * 4 > 5 * 7 – 1 (2) multiplication 3 + 16 > 5 * 7 – 1 (3) multiplication 3 + 16 > 35 – 1 (4) addition 19 > 35 – 1 (5) subtraction 19 > 34 (6) greater than false Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 65
  66. 66. CompanionWebsite Operand Evaluation Order Supplement III.A, “Advanced discussions on how an expression is evaluated in the JVM.” Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 66
  67. 67. (GUI) Confirmation Dialogsint option = JOptionPane.showConfirmDialog (null, "Continue"); Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 67
  68. 68. Problem: Guessing Birth DateThe program can guess your birth date. Runto see how it works. = 19 + 1 3 5 7 2 3 6 7 4 5 6 7 8 9 10 11 16 17 18 19 9 11 13 15 10 11 14 15 12 13 14 15 12 13 14 15 20 21 22 2317 19 21 23 18 19 22 23 20 21 22 23 24 25 26 27 24 25 26 2725 27 29 31 26 27 30 31 28 29 30 31 28 29 30 31 28 29 30 31 Set1 Set2 Set3 Set4 Set5 GuessBirthdayUsingConfirmationDialog Run Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 68

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