1. Chapter 8 Conditionals

2. Learning Java through Alice © Daly and Wrigley Objectives List relational operators. List logical operators. Use the hierarchy of operators chart to properly construct if/else statements. Construct switch statements. Use nested if statements. 2

3. Learning Java through Alice © Daly and Wrigley Decisions True and false values are also known as Boolean values, named after the 19th century English mathematician George Boole. 3

4. Learning Java through Alice © Daly and Wrigley Relational Operators A Boolean test compares primitives, constants, and variables and or objects using the following relational operators: OperatorMeaningExample ==Equal tox == 3 ! =Not equal tox != 3 <Less thanx < 3 >Greater thanx > 3 <=Less than or equal tox <= 3 >=Greater than or equal tox >= 3 Note: These relational operators must be typed exactly as above. You can’t type a space between the two equal signs and you can’t put =< to mean less than or equal. 4

5. Learning Java through Alice © Daly and Wrigley Alice Example of an if statement : 5

6. Learning Java through Alice © Daly and Wrigley Logical Operators Logical OperatorExplanation: && Logical AND - Both conditions on both sides of the && must be true for the result to be TRUE. The first condition will be tested and if it is false, the computer will not bother to test the second condition since there is no way for both conditions to be true if the first condition is false.. || Logical OR - If either condition is true on both sides of the || then the result is true. The first condition will be tested and if it is true, the computer will not bother to test the second condition since it only needs one condition to be true and it already found one to be true. &Boolean AND -Same as logical AND but it tests both sides of & no matter what. |Boolean OR - Same as logical OR but it tests both side of | no matter what. ! Logical NOT - Negates the condition (i.e. - if result was false, it will become true and vice versa. ^ Boolean logical exclusive OR - Results in true value if and only if one of its operands is true and the other is false. 6

7. Learning Java through Alice © Daly and Wrigley If Statements The syntax contains the keyword if, followed by a condition (boolean test) in parenthesis, followed by either a single statement or a block statement to execute if the test is true. An optional else keyword provides the alternative statement to execute if the test is false. if (condition) { statements to do when conditional is true } else { statements to do when conditional is false } 7

8. Learning Java through Alice © Daly and Wrigley If Statements Examples if (x < y) { System.out.println ( "x is smaller than y" ); } else { System.out.println ("x is not smaller than y" ); } 8

9. Learning Java through Alice © Daly and Wrigley If Statements Examples Continued… if ( guess == correctAnswer ) { score = score + 10; System.out.println ( "You are right. You get 10 points."); } else { score = score - 5; System.out.println ( "Sorry, that is wrong. You lose 5 points."); } 9

10. Learning Java through Alice © Daly and Wrigley Else If if (x < 0) { System.out.println ( "X is negative." ); } else if (x == 0) { System.out.println ( "X is equal to 0." ); } else { System.out.println ( "X is positive." ); } 10

11. Learning Java through Alice © Daly and Wrigley Using Logical Operators The following only prints if x is less than y and x is less than z. The && means if x is NOT less than y it won't even bother to test to see if x is less than z. if ( x < y && x < z) { System.out.println ("x is less than both y and z" ); } The following calculates grossPay if either condition is true. The || means that if weeklyHours is less 40, it won't bother to test to see if employeeType is 'P'. if (weeklyHours < 40 || employeeType == 'P' ) { grossPay = weeklyHours * hourlyRate; } 11

12. Learning Java through Alice © Daly and Wrigley Switch Statements Done with if statements:Done with switch statements: if (grade == 'A') { System.out.println("Great!"); } else if (grade == 'B') { System.out.println("Good!"); } else if (grade == 'C') { System.out.println("Nice."); } else { System.out.println("Not Good."); } switch (grade) { case 'A': System.out.println("Great!"); break; case 'B': System.out.println("Good!"); break; case 'C': System.out.println("Nice."); break; default: System.out.println("Not Good."); } 12

13. Learning Java through Alice © Daly and Wrigley Complex If Statements vs. Switch Complex If Statements:Switch Statements: if (month == 2) { days =28; } else if ((month == 4) || (month == 6) || (month == 9) || (month == 11)) { days=30; } else { days=31; } switch (month) { case 2: days = 28; break; case 4: case 6: case 9: case 11: days = 30; break; default: days = 31; } 13

14. Learning Java through Alice © Daly and Wrigley Comparing Strings using if/else 14

15. Learning Java through Alice © Daly and Wrigley Comparing Strings using the Switch 15