1. Java Programming: From Problem Analysis to Program Design, 5e Chapter 4 Control Structures I: Selection

2. Chapter Objectives

Learn about control structures

Examine relational and logical operators

Explore how to form and evaluate logical (Boolean) expressions

Learn how to use the selection control structuresif ,if else , andswitchin a program

Java Programming: From Problem Analysis to Program Design, 5e 3. Control Structures

Three methods of processing a program

• In sequence

• Branching

• Looping

Branch:altering the flow of program execution by making a selection or choice

Loop: altering the flow of program execution by repetition of statement(s)

Java Programming: From Problem Analysis to Program Design, 5e 4. Flow of Execution Java Programming: From Problem Analysis to Program Design, 5e 5. Relational Operators

Relational operator

• Allows you to make comparisons in a program

• Binary operator

Condition is represented by a logical expression in Java

Logical expression: expression that has a value of either true or false

Java Programming: From Problem Analysis to Program Design, 5e 6. Relational Operators in Java Java Programming: From Problem Analysis to Program Design, 5e 7. Relational Operators and Primitive Data Types

Can be used with integral and floating-point data types

Can be used with the char data type

Unicode collating sequence

Java Programming: From Problem Analysis to Program Design, 5e 8. Java Programming: From Problem Analysis to Program Design, 5e 9. Java Programming: From Problem Analysis to Program Design, 5e 10. Relational Operators and the Unicode Collating Sequence Java Programming: From Problem Analysis to Program Design, 5e 11. Logical (Boolean) Operators Java Programming: From Problem Analysis to Program Design, 5e 12. Logical (Boolean) Operators (continued) Java Programming: From Problem Analysis to Program Design, 5e 13. Logical (Boolean) Operators (continued) Java Programming: From Problem Analysis to Program Design, 5e 14. Logical (Boolean) Operators (continued) Java Programming: From Problem Analysis to Program Design, 5e 15. Precedence of Operators Java Programming: From Problem Analysis to Program Design, 5e 16. Precedence of Operators (continued) Java Programming: From Problem Analysis to Program Design, 5e 17. Java Programming: From Problem Analysis to Program Design, 5e 18. Java Programming: From Problem Analysis to Program Design, 5e 19. Java Programming: From Problem Analysis to Program Design, 5e 20. Selection

One-way selection

Two-way selection

Compound (block of) statements

Multiple selections (nested if)

Conditional operator

switchstructures

Java Programming: From Problem Analysis to Program Design, 5e 21. One-Way Selection

Syntax

if(expression)

statement

Expression referred to as decision maker

Statement referred to as action statement

Java Programming: From Problem Analysis to Program Design, 5e 22. One-Way Selection (continued) Java Programming: From Problem Analysis to Program Design, 5e 23.

Example 4-7

//Program to determine the absolute value of an integer

importjavax.swing.JOptionPane;

public classAbsoluteValue

{

public static voidmain(String[] args)

{

intnumber;

inttemp;

String numString;

numString =

JOptionPane.showInputDialog

("Enter an integer:");//Line 1

number = Integer.parseInt(numString);//Line 2

temp = number;//Line 3

One-Way Selection (continued) Java Programming: From Problem Analysis to Program Design, 5e 24.

if(number < 0)//Line 4

number = -number;//Line 5

JOptionPane.showMessageDialog(null,

"The absolute value of " + temp

+ " is " + number,

"Absolute Value",

JOptionPane.INFORMATION_MESSAGE); //Line 6

System.exit(0);

}

One-Way Selection (continued) Java Programming: From Problem Analysis to Program Design, 5e 25.

if(number < 0)//Line 4

number = -number;//Line 5

JOptionPane.showMessageDialog(null,

"The absolute value of " + temp

+ " is " + number,

"Absolute Value",

JOptionPane.INFORMATION_MESSAGE); //Line 6

System.exit(0);

}

Java Programming: From Problem Analysis to Program Design, 5e 26. Two-Way Selection

Syntax

if(expression)

statement1

else

statement2

elsestatement must be paired with anif

Java Programming: From Problem Analysis to Program Design, 5e 27. Two-Way Selection (continued) Java Programming: From Problem Analysis to Program Design, 5e 28. Two-Way Selection (continued) Java Programming: From Problem Analysis to Program Design, 5e Example 4-10 if(hours > 40.0) wages = 40.0 * rate +1.5 * rate * (hours - 40.0);else wages = hours * rate; 29. Two-Way Selection (continued) Java Programming: From Problem Analysis to Program Design, 5e

Example 4-11

if(hours > 40.0);//Line 1

wages = 40.0 * rate +

1.5 * rate * (hours - 40.0);//Line 2

else //Line 3

wages = hours * rate;//Line 4

Because a semicolon follows the closing parenthesis of theifstatement (Line 1), theelsestatement stands alone

The semicolon at the end of theifstatement (see Line 1) ends theifstatement, so the statement at Line 2 separates the else clause from theifstatement; that is,elseis by itself

Since there is no separateelsestatement in Java, this code generates a syntax error

30. Two-Way Selection (continued) Java Programming: From Problem Analysis to Program Design, 5e 31. Compound (Block of) Statements

Syntax

Java Programming: From Problem Analysis to Program Design, 5e 32. Compound (Block of) Statements (continued)

if(age > 18)

{

System.out.println("Eligible to vote.");

System.out.println("No longer a minor.");

}

else

{

System.out.println("Not eligible to vote.");

System.out.println("Still a minor.");

}

Java Programming: From Problem Analysis to Program Design, 5e 33. Multiple Selection: Nested if

Syntax

if(expression1)

statement1

else if(expression2)

statement2

else

statement3

Else associated with most recent incomplete if

Multiple if statements can be used in place of ifelse statements

May take longer to evaluate

Java Programming: From Problem Analysis to Program Design, 5e 34. Multiple Selection: Nested if (continued) Java Programming: From Problem Analysis to Program Design, 5e 35. Multiple Selection: Nested if (continued) Java Programming: From Problem Analysis to Program Design, 5e To avoid excessive indentation, the code in Example 4-15 can be rewritten as follows: 36. Multiple Selection: Nested if (continued) Java Programming: From Problem Analysis to Program Design, 5e 37. Multiple Selection: Nested if (continued) Java Programming: From Problem Analysis to Program Design, 5e 38. Java Programming: From Problem Analysis to Program Design, 5e 39. Java Programming: From Problem Analysis to Program Design, 5e 40.

Definition:a process in which the computer evaluates a logical expression from left to right and stops as soon as the value of the expression is known

Short-Circuit Evaluation Java Programming: From Problem Analysis to Program Design, 5e 41. Short-Circuit Evaluation (continued) Java Programming: From Problem Analysis to Program Design, 5e 42. Java Programming: From Problem Analysis to Program Design, 5e 43. Java Programming: From Problem Analysis to Program Design, 5e 44. Java Programming: From Problem Analysis to Program Design, 5e 45. Java Programming: From Problem Analysis to Program Design, 5e

The preceding program and its output show that you should be careful when comparing floating-point numbers for equality.

One way to check whether two floating-point numbers are equal is to check whether the absolute value of their difference is less than a certain tolerance. For example, suppose the tolerance is.000001 .

Thenxandyare equal if the absolute value of(x y)is less than0.000001 . To find the absolute value, you can use the functionMath.absof theclass Math , as shown in the program.

Therefore, the expressionMath.abs(x y) < 0.000001determines whether the absolute value of (x y) is less than 0.000001.

46. Conditional (? :) Operator

Ternary operator

Syntax

expression1 ?expression2:expression3

Ifexpression1 =true , then the result of the condition is expression 2; otherwise, the result of the condition is expression 3

Java Programming: From Problem Analysis to Program Design, 5e 47. Java Programming: From Problem Analysis to Program Design, 5e 48. Java Programming: From Problem Analysis to Program Design, 5e 49. Java Programming: From Problem Analysis to Program Design, 5e 50. Java Programming: From Problem Analysis to Program Design, 5e 51. switchStructures Java Programming: From Problem Analysis to Program Design, 5e 52. switchStructures (continued) Java Programming: From Problem Analysis to Program Design, 5e

In Java,switch ,case ,break , anddefaultare reserved words

In aswitchstructure, the expression is evaluated first

The value of the expression is then used to perform the actions specified in the statements that follow the reserved wordcase

The expression is usually an identifier

The value of the identifier or the expression can be only of typeint ,byte ,short , orchar

53. switchStructures (continued) Java Programming: From Problem Analysis to Program Design, 5e

The expression is sometimes called the selector; its value determines which statements are selected for execution

A particularcasevalue must appear only once

One or more statements may follow acaselabel, so you do not need to use braces to turn multiple statements into a single compound statement

54. switchStructures (continued) Java Programming: From Problem Analysis to Program Design, 5e

Thebreakstatement may or may not appear after eachstatements1 ,statements2 , ...,statementsn

Aswitchstructure may or may not have thedefaultlabel

55. switchStructures (continued) Java Programming: From Problem Analysis to Program Design, 5e 56. switchStructures (continued) Java Programming: From Problem Analysis to Program Design, 5e 57.

Example 4-20

switch(grade)

{

case'A':

System.out.println("The grade is A.");

break ;

case'B':

System.out.println("The grade is B.");

break ;

case'C':

System.out.println("The grade is C.");

break ;

switchStructures (continued) Java Programming: From Problem Analysis to Program Design, 5e 58.

case'D':

System.out.println("The grade is D.");

break ;

case'F':

System.out.println("The grade is F.");

break ;

default :

System.out.println("The grade is invalid.");

}

switchStructures (continued) Java Programming: From Problem Analysis to Program Design, 5e 59. Java Programming: From Problem Analysis to Program Design, 5e 60. Java Programming: From Problem Analysis to Program Design, 5e 61. Java Programming: From Problem Analysis to Program Design, 5e 62. Java Programming: From Problem Analysis to Program Design, 5e To output results correctly, theswitchstructure must include abreakstatement after eachprintlnstatement, except the lastprintlnstatement. 63. Programming Example:Cable Company Billing

Input: customers account number, customer code, number of premium channels to which customer subscribes, number of basic service connections (in case of business customers)

Output: customers account number and the billing amount

Java Programming: From Problem Analysis to Program Design, 5e 64. Programming Example:Cable Company Billing (continued)

Solution

• Prompt user for information

• Use switch statements based on customers type

• Use an if statement nested within a switch statement to determine amount due by each customer

Java Programming: From Problem Analysis to Program Design, 5e 65. Comparing Strings

class String

• MethodcompareTo

• Methodequals

Given stringstr1andstr2

Java Programming: From Problem Analysis to Program Design, 5e 66. Comparing Strings (continued)

String str1 = "Hello";

String str2 = "Hi";

String str3 = "Air";

String str4 = "Bill";

String str5 = "Bigger";

Java Programming: From Problem Analysis to Program Design, 5e 67. Comparing Strings (continued) Java Programming: From Problem Analysis to Program Design, 5e 68. Comparing Strings (continued) Java Programming: From Problem Analysis to Program Design, 5e 69. Chapter Summary

Control structures are used to process programs

Logical expressions and order of precedence of operators are used in expressions

If statements

if elsestatements

switchstructures

Proper syntax for using control statements

Compare strings

Java Programming: From Problem Analysis to Program Design, 5e