Branching. Chapter 5 11/14/16 & 11/15/16

Transcription

1 Branching Chapter 5 11/14/16 & 11/15/16

2 Chapter Contents Flow of Control The if Statement Compound Statements Basic Comparisons Comparing Primitives Comparing Objects

3 Chapter Contents The if-else Statement Logical Operators

4 Flow of Control Statements normally executed in sequence From first to last This sequence can be altered A statement may call another method Decision statements cause different sequences to be followed

5 Flow of Control Figure 7-1 Invoking a method

6 If Statement int broncos = 24; int lobos = 31; if(broncos < lobos) System.out.println("Broncos lose!"); System.out.println("Good Night!");

7 The if Statement Specify a condition If condition is true one or more statements execute If condition is false these statements skipped Syntax

8 The if Statement Figure 7-2 The logic of an if statement

9 Basic Comparisons Figure 7-3 Relational operators that compare primitive values

10 Write a Program Write a program to ask the user for her age. Output Old Enough to Join the Army if she is 18 or older. Next output a message that says Army Strong..

11 Participation Write a class called Thermometer. Give the class a parameterized constructor that initializes the temperature. If the value passed to the constructor is greater that 135, output Record High!. No need to write any more methods. Write a tester to test the constructor.

12 Compound Statements When if statement requires multiple statements to execute Enclose those multiple statements within braces { } after if (condition) if(resp == YES){ System.out.println("Evaluate Launch Conditions."); System.out.println("Respond as prompted"); System.out.println("call "); }

13 Comparing Objects Methods equals for String Object variable does not contain object Object variable contains reference to it Thus, == operator Compares references Not values

14 Comparing Objects String friend = "Sam"; //String with same data String name = new String("Sam"); if(friend!= name) //Compares addresses System.out.println("Not the same object!"); if(friend.equals(name)) System.out.println ("Words in objects are equal.");

15 Comparing Objects Distinct references to strings whose values are the same

16 Comparing Objects Two variables containing equal references to the same string

17 If-else & Logical Operators

18 A Program with else A program that asks the user whether the user wants a quote by Turing or another quote. For Turing output:"machines take me by surprise with great frequency.- Turing" For other output:"intelligence is the ability to adapt to change.-hawking" BrainyQuotes.java

19 import java.util.scanner; public class BrainyQuotes { public static void main(string[] args) { Scanner scan = new Scanner(System.in); System.out.println("Would you like a Turing quote?"); String ans = scan.next(); if(ans.equals("yes")) System.out.println("Machines take me" + " by surprise with great frequency.--turing"); else System.out.println("Intelligence is" + " the ability to adapt to change.--hawking"); } scan.close(); } //Note:next( ) inputs a String up to the next whitespace.

20 The if-else Statement When you wish to do one thing if the condition is true But you want to do something else when the condition is false Syntax

21 The if-else Statement The logic of an if-else statement

22 Write an if-else Statement Write an if else statement that assigns 0.1 to commission unless sales is greater that or equal to , in which case it assigns 0.2 to commission.

23 Logical Operators

24 Logical Operators Logical operators Used to combine boolean expressions Extra parenthesis are optional. 20 <= age < 30 doesn't work

25 Logical Operators The operator &&

26 Logical Operators The operator

27 Logical Operators The operator!! true -> false!("joe".equals("joe"))! false -> true!("sam".equals("joe"))

28 Precedence for Ops Order of operations in a logical expression

29 Wrap Up Question 1)How do you best compare two Strings to see if they are equal?

30 Participation Write a program to input the measures of three sides of a triangle. Output a statement the says it is either equilateral or not equilateral after comparing the sides.

31 import java.util.scanner; public class Equilateral { public static void main(string[] args) { Scanner scan = new Scanner(System.in); //Input the side measures System.out.print("Enter Side A:"); double sidea = scan.nextdouble(); System.out.print("Enter Side B:"); double sideb = scan.nextdouble(); System.out.print("Enter Side C:"); double sidec = scan.nextdouble(); //Find out if it is equilateral } }

32 Branching Chapter 5