java switch
- 1. 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
- 2. Objectives • Learn useful selection and repetition statement • Use primitive types and operators • Use the Math library • Build software using an iterative development cycle
- 3. 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)
- 4. 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
- 5. Symbol Meaning Example && conditional AND (age > 20) && (age < 35) || conditional OR (height > 78.5) || (weight > 300) Figure 4.2 Conditional Operators
- 6. 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
- 7. A B A && B true true true true false false false (don't care) false Figure 4.4 Evaluating a conditional AND expression
- 8. 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
- 9. A B A || B true (don't care) true false true true false false false Figure 4.6 Evaluating a condition OR expression
- 10. A !A true false false true Figure 4.7 Evaluating a logical complement expression
- 11. Figure 4.8 Operator precedence* Highest NOT! ! multiplicative * / % additive + - relational < > <= >= equality == != conditional AND && conditional OR || assignment = += -= *= /= %= Lowest
- 12. 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
- 13. 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)
- 14. 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");
- 15. 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");
- 16. Figure 4.12 Flow chart for nested if-else statements Last? Last false code ... Last true code True False False Test1? Test2? Test1 true code Test2 true code True True False False
- 17. 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
- 18. 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
- 19. 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");
- 20. 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
- 21. 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
- 22. 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
- 23. 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"); }
- 24. 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
- 25. The For Statement • The for statement is equivalent to the following while loop structure initialization ; 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
- 26. 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;
- 27. 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
- 28. 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;
- 29. 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;
- 30. Figure 4.21 Declaring an index variable before the for loop int i; // declare loop index int sum = 0; for (i = 4; i >= 1; i--) // initialize loop index sum += i; ... i += 17; // use variable i
- 31. Examples • TwelveDays.java (extra) • Diamond.java (extra) • Growth.java • Mortgage.java (extra)
- 32. 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
- 33. Figure 4.22 Syntax for the do-while statement do statement while (condition) ;
- 34. 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)
- 35. 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);
- 36. 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
- 37. 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
- 38. 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
- 39. 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
- 40. 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
- 41. 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; // valid float ok = (float)4.25; // valid float bad = 4.25; // invalid
- 42. 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 functions abs - 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
- 43. 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 number random() - Returns a double value with a positive sign, greater than or equal to 0.0 and less than 1.0
- 44. 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 conversion toDegrees(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
- 45. The Math Class • Library.java • Toss.java • CoinToss.java
- 46. Figure 4.25 Size of the reward given each day 1 1 2 4 8 12 16 16 8 4 2 Days
- 47. Figure 4.26 Using random numbers to represent heads and tails 0.0 0.5 1.0 HHHHHHHHHHHHHHHHHTTTTTTTTTTTTTTTTTT Heads Tails
- 48. Iterative Development Cycle • First iteration - CovertMenu.java (with stubs for methods) • Second iteration - CovertFromMetric.java (implement MetricToEnglish()) • Third iteration - Convert.java (implement EnglishToMetric())
- 49. 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);
- 50. 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);
- 51. 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);
- 52. 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.
- 53. 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;
- 54. 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;