Lesson 38: Conditionals #2 (W11D3)

Transcription

1 Lesson 38: Conditionals #2 (W11D3) Balboa High School Michael Ferraro October 28, / 61

2 Do Now In Lesson38/DoNow.java, write a method called isdivisiblebyfour() that takes an int returns the boolean values true or false indicating whether the input value is evenly divisible by 4. Once finished, have main() call isdivisiblebyfour() using the following for() loop: for(int i = 0 ; i <= 100 ; i++) { if ( isdivisiblebyfour(i) ) { System.out.println(i+" is divisible by 4"); } } 2 / 61

3 Aim Students will learn how to perform basic logic operations (and, or, & not) in Java and how Java s order of operations works with respect to relational (e.g., <, <=, &!=) and logical operators. 3 / 61

4 Basic Logic: && (and) How does and work in logic? 4 / 61

5 Basic Logic: && (and) How does and work in logic? I work really hard and I get good grades. (p && q) 5 / 61

6 Basic Logic: && (and) How does and work in logic? I work really hard and I get good grades. (p && q) Evaluate the value of the boolean expression ( p && q ) when... 6 / 61

7 Basic Logic: && (and) How does and work in logic? I work really hard and I get good grades. (p && q) Evaluate the value of the boolean expression ( p && q ) when... 1 p = true, q = true 7 / 61

8 Basic Logic: && (and) How does and work in logic? I work really hard and I get good grades. (p && q) Evaluate the value of the boolean expression ( p && q ) when... 1 p = true, q = true 2 p = true, q = false 8 / 61

9 Basic Logic: && (and) How does and work in logic? I work really hard and I get good grades. (p && q) Evaluate the value of the boolean expression ( p && q ) when... 1 p = true, q = true 2 p = true, q = false 3 p = false, q = true 9 / 61

10 Basic Logic: && (and) How does and work in logic? I work really hard and I get good grades. (p && q) Evaluate the value of the boolean expression ( p && q ) when... 1 p = true, q = true 2 p = true, q = false 3 p = false, q = true 4 p = false, q = false 10 / 61

11 Basic Logic: && (and) How does and work in logic? I work really hard and I get good grades. (p && q) Evaluate the value of the boolean expression ( p && q ) when... 1 p = true, q = true 2 p = true, q = false 3 p = false, q = true 4 p = false, q = false && is true when both operands (inputs) are true. 11 / 61

12 Basic Logic: (or) How does or work in logic? 1 or is also true when both operands are true when using inclusive or 12 / 61

13 Basic Logic: (or) How does or work in logic? I m a slacker or I get good grades. (p q) 1 or is also true when both operands are true when using inclusive or 13 / 61

14 Basic Logic: (or) How does or work in logic? I m a slacker or I get good grades. (p q) Evaluate the value of the expression ( p q ) when... 1 or is also true when both operands are true when using inclusive or 14 / 61

15 Basic Logic: (or) How does or work in logic? I m a slacker or I get good grades. (p q) Evaluate the value of the expression ( p q ) when... 1 p = true, q = true 1 or is also true when both operands are true when using inclusive or 15 / 61

16 Basic Logic: (or) How does or work in logic? I m a slacker or I get good grades. (p q) Evaluate the value of the expression ( p q ) when... 1 p = true, q = true 2 p = true, q = false 1 or is also true when both operands are true when using inclusive or 16 / 61

17 Basic Logic: (or) How does or work in logic? I m a slacker or I get good grades. (p q) Evaluate the value of the expression ( p q ) when... 1 p = true, q = true 2 p = true, q = false 3 p = false, q = true 1 or is also true when both operands are true when using inclusive or 17 / 61

18 Basic Logic: (or) How does or work in logic? I m a slacker or I get good grades. (p q) Evaluate the value of the expression ( p q ) when... 1 p = true, q = true 2 p = true, q = false 3 p = false, q = true 4 p = false, q = false 1 or is also true when both operands are true when using inclusive or 18 / 61

19 Basic Logic: (or) How does or work in logic? I m a slacker or I get good grades. (p q) Evaluate the value of the expression ( p q ) when... 1 p = true, q = true 2 p = true, q = false 3 p = false, q = true 4 p = false, q = false is true when either operand (input) is true. 1 1 or is also true when both operands are true when using inclusive or 19 / 61

20 Examples Predict the output of the following: boolean p = true; //I like to sing boolean q = false; //I like to dance if( p q ) { System.out.println("Perform for us!"); } else { System.out.println("Get off the stage!"); } 20 / 61

21 Examples Predict the output of the following: boolean p = false; boolean q = false; //I like to sing //I like to dance if( p q ) { System.out.println("Perform for us!"); } else { System.out.println("Get off the stage!"); } 21 / 61

22 Examples Predict the output of the following: boolean p = false; boolean q = true; //I like to sing //I like to dance if( p && q ) { System.out.println("Perform for us!"); } else { System.out.println("Get off the stage!"); } 22 / 61

23 Examples Predict the output of the following: boolean p = true; boolean q = true; //I like to sing //I like to dance if( p && q ) { System.out.println("Perform for us!"); } else { System.out.println("Get off the stage!"); } 23 / 61

24 Using and and or Write a boolean expression that evaluates to true when a number is between 0 and 9, inclusive / 61

25 Using and and or Write a boolean expression that evaluates to true when a number is between 0 and 9, inclusive... Restated: true when a number is 0 and 9 25 / 61

26 Using and and or Write a boolean expression that evaluates to true when a number is between 0 and 9, inclusive... Restated: true when a number is 0 and 9 Solution: For a number, n, ( n >= 0 ) && ( n <= 9 ) 26 / 61

27 Using and and or Write a boolean expression that evaluates to true when a number is between 0 and 9, inclusive... Restated: true when a number is 0 and 9 Solution: For a number, n, ( n >= 0 ) && ( n <= 9 ) As used in an if() statement: if ( ( n >= 0 ) && ( n <= 9 ) ) {... } 27 / 61

28 Using and and or Write a boolean expression that evaluates to true when a number is less than 5 or greater than 6, exclusive Excluding the values 5 and 6, i.e., the number is strictly less than 5 or strictly greater than 6, and equal to neither. 28 / 61

29 Using and and or Write a boolean expression that evaluates to true when a number is less than 5 or greater than 6, exclusive 2... Restated: true when a number is < 5 or > 6 2 Excluding the values 5 and 6, i.e., the number is strictly less than 5 or strictly greater than 6, and equal to neither. 29 / 61

30 Using and and or Write a boolean expression that evaluates to true when a number is less than 5 or greater than 6, exclusive 2... Restated: true when a number is < 5 or > 6 Solution: For a number, n, ( n < 5 ) ( n > 6 ) 2 Excluding the values 5 and 6, i.e., the number is strictly less than 5 or strictly greater than 6, and equal to neither. 30 / 61

31 Basic Logic:! (not)! is the not, or negation, operator It flips a boolean s truth value boolean isempty = true; //glass is empty if (! isempty ) { takesip(); } else { refillglass(); } 31 / 61

32 Basic Logic:! (not)! is the not, or negation, operator It flips a boolean s truth value boolean isempty = true; //glass is empty if (! isempty ) { takesip(); } else { refillglass(); }! is referred to as an unary operator 32 / 61

33 Basic Logic:! (not)! is the not, or negation, operator It flips a boolean s truth value boolean isempty = true; //glass is empty if (! isempty ) { takesip(); } else { refillglass(); }! is referred to as an unary operator unary means that it takes one operand the values whose truth value is to be flipped 33 / 61

34 Basic Logic:! (not)! is the not, or negation, operator It flips a boolean s truth value boolean isempty = true; //glass is empty if (! isempty ) { takesip(); } else { refillglass(); }! is referred to as an unary operator unary means that it takes one operand the values whose truth value is to be flipped cf. binary operators like +, -, *, /, %,, etc. 34 / 61

35 Mixing Logical Operators Determine the value of c. boolean a = true; boolean b = false; boolean c = ( a &&!b ); 35 / 61

36 Mixing Logical Operators Determine the value of c. boolean a = true; boolean b = true; boolean c = (!a!b ); 36 / 61

37 Mixing Logical Operators Are things any different now? boolean a = true; boolean b = true; //boolean c = (!a!b ); boolean c =!( a && b ); 37 / 61

38 Mixing Logical Operators Are things any different now? boolean a = true; boolean b = true; //boolean c = (!a!b ); boolean c =!( a && b ); We ll revisit this shortly / 61

39 Revisiting the Example Write a boolean expression that evaluates to true when a number is less than 5 or greater than 6, exclusive: ( n < 5 ) ( n > 6 ) 39 / 61

40 Revisiting the Example Write a boolean expression that evaluates to true when a number is less than 5 or greater than 6, exclusive: ( n < 5 ) ( n > 6 ) In other words, true when n is < > n 40 / 61

41 Revisiting the Example Write a boolean expression that evaluates to true when a number is less than 5 or greater than 6, exclusive: ( n < 5 ) ( n > 6 ) In other words, true when n is < > n Isn t it reasonable to say the following instead? It is not true that n is between 5 and 6, inclusive! ( ( n >= 5 ) && ( n <= 6 ) ) 41 / 61

42 Revisiting the Example Write a boolean expression that evaluates to true when a number is less than 5 or greater than 6, exclusive: ( n < 5 ) ( n > 6 ) In other words, true when n is < > n Isn t it reasonable to say the following instead? It is not true that n is between 5 and 6, inclusive! ( ( n >= 5 ) && ( n <= 6 ) ) both boolean expressions are logically equivalent 42 / 61

43 DeMorgan s Rules The rules are fully described in PS #6, / 61

44 DeMorgan s Rules The rules are fully described in PS #6, Summary: Distribute the negation, swap the and/or 44 / 61

45 DeMorgan s Rules The rules are fully described in PS #6, Summary: Distribute the negation, swap the and/or! ( A B )!A &&!B 45 / 61

46 DeMorgan s Rules The rules are fully described in PS #6, Summary: Distribute the negation, swap the and/or! ( A B )!A &&!B! ( A && B )!A!B 46 / 61

47 DeMorgan s Rules The rules are fully described in PS #6, Summary: Distribute the negation, swap the and/or! ( A B )!A &&!B! ( A && B )!A!B Example: 47 / 61

48 DeMorgan s Rules The rules are fully described in PS #6, Summary: Distribute the negation, swap the and/or! ( A B )!A &&!B! ( A && B )!A!B Example:!( a && b ) 48 / 61

49 DeMorgan s Rules The rules are fully described in PS #6, Summary: Distribute the negation, swap the and/or! ( A B )!A &&!B! ( A && B )!A!B Example:!( a && b )!a!b 49 / 61

50 Second DeMorgan s Example!( ( n >= 5 ) && ( n <= 6 ) ) 50 / 61

51 Second DeMorgan s Example!( ( n >= 5 ) && ( n <= 6 ) )!( n >= 5 )!( n <= 6 ) 51 / 61

52 Second DeMorgan s Example!( ( n >= 5 ) && ( n <= 6 ) )!( n >= 5 )!( n <= 6 )!( n >= 5 )!( n <= 6 ) 52 / 61

53 Second DeMorgan s Example!( ( n >= 5 ) && ( n <= 6 ) )!( n >= 5 )!( n <= 6 )!( n >= 5 )!( n <= 6 ) ( n < 5 ) ( n > 6 ) 53 / 61

54 Java Order of Operations When do we need ()s? When don t we? 54 / 61

55 Java Order of Operations Priority Operator Type Operators highest Pemdas () Unary!,, casts, ++, pemdas pemdas, (also modulo, %) pemdas +, Relational Operators <, <=, >, >=, ==,! = Logical and && lowest Logical or x y 55 / 61

56 Java Order of Operations Let s see if we can simplify some earlier examples / 61

57 Java Order of Operations Let s see if we can simplify some earlier examples... ( n >= 0 ) && ( n <= 9 ) are ()s needed? 57 / 61

58 Java Order of Operations Let s see if we can simplify some earlier examples... ( n >= 0 ) && ( n <= 9 ) are ()s needed? n >= 0 && n <= 9 58 / 61

59 Java Order of Operations Let s see if we can simplify some earlier examples... ( n >= 0 ) && ( n <= 9 ) are ()s needed? n >= 0 && n <= 9 ( n < 5 ) ( n > 6 ) are ()s needed? 59 / 61

60 Java Order of Operations Let s see if we can simplify some earlier examples... ( n >= 0 ) && ( n <= 9 ) are ()s needed? n >= 0 && n <= 9 ( n < 5 ) ( n > 6 ) are ()s needed? n < 5 n > 6 60 / 61

61 HW Complete of PS #6, inclusive The reading for Litvin Ch. 6 is available here. 61 / 61