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    9781111530532 ppt ch04 9781111530532 ppt ch04 Presentation Transcript

    • Java Programming: From Problem Analysis to Program Design, 5e Chapter 4 Control Structures I: Selection
    • 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 structures if , if … else , and switch in a program
      Java Programming: From Problem Analysis to Program Design, 5e
    • 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
    • Flow of Execution Java Programming: From Problem Analysis to Program Design, 5e
    • 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
    • Relational Operators in Java Java Programming: From Problem Analysis to Program Design, 5e
    • 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
    • Java Programming: From Problem Analysis to Program Design, 5e
    • Java Programming: From Problem Analysis to Program Design, 5e
    • Relational Operators and the Unicode Collating Sequence Java Programming: From Problem Analysis to Program Design, 5e
    • Logical (Boolean) Operators Java Programming: From Problem Analysis to Program Design, 5e
    • Logical (Boolean) Operators (continued) Java Programming: From Problem Analysis to Program Design, 5e
    • Logical (Boolean) Operators (continued) Java Programming: From Problem Analysis to Program Design, 5e
    • Logical (Boolean) Operators (continued) Java Programming: From Problem Analysis to Program Design, 5e
    • Precedence of Operators Java Programming: From Problem Analysis to Program Design, 5e
    • Precedence of Operators (continued) Java Programming: From Problem Analysis to Program Design, 5e
    • Java Programming: From Problem Analysis to Program Design, 5e
    • Java Programming: From Problem Analysis to Program Design, 5e
    • Java Programming: From Problem Analysis to Program Design, 5e
    • Selection
      • One-way selection
      • Two-way selection
      • Compound (block of) statements
      • Multiple selections (nested if)
      • Conditional operator
      • switch structures
      Java Programming: From Problem Analysis to Program Design, 5e
    • 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
    • One-Way Selection (continued) Java Programming: From Problem Analysis to Program Design, 5e
      • Example 4-7
      • //Program to determine the absolute value of an integer
      • import javax.swing.JOptionPane;
      • public class AbsoluteValue
      • {
      • public static void main(String[] args)
      • {
      • int number;
      • int temp;
      • 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
      • if (number < 0) //Line 4
      • number = -number; //Line 5
      • JOptionPane.showMessageDialog(null,
      • &quot;The absolute value of &quot; + temp
      • + &quot; is &quot; + number,
      • &quot;Absolute Value&quot;,
      • JOptionPane.INFORMATION_MESSAGE); //Line 6
      • System.exit(0);
      • }
      One-Way Selection (continued) Java Programming: From Problem Analysis to Program Design, 5e
      • if (number < 0) //Line 4
      • number = -number; //Line 5
      • JOptionPane.showMessageDialog(null,
      • &quot;The absolute value of &quot; + temp
      • + &quot; is &quot; + number,
      • &quot;Absolute Value&quot;,
      • JOptionPane.INFORMATION_MESSAGE); //Line 6
      • System.exit(0);
      • }
      Java Programming: From Problem Analysis to Program Design, 5e
    • Two-Way Selection
      • Syntax
      • if (expression)
      • statement1
      • else
      • statement2
      • else statement must be paired with an if
      Java Programming: From Problem Analysis to Program Design, 5e
    • Two-Way Selection (continued) Java Programming: From Problem Analysis to Program Design, 5e
    • 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;
    • 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 the if statement (Line 1), the else statement stands alone
      • The semicolon at the end of the if statement (see Line 1) ends the if statement, so the statement at Line 2 separates the else clause from the if statement; that is, else is by itself
      • Since there is no separate else statement in Java, this code generates a syntax error
    • Two-Way Selection (continued) Java Programming: From Problem Analysis to Program Design, 5e
    • Compound (Block of) Statements
      • Syntax
      Java Programming: From Problem Analysis to Program Design, 5e
    • Compound (Block of) Statements (continued)
      • if (age > 18)
      • {
      • System.out.println(&quot;Eligible to vote.&quot;);
      • System.out.println(&quot;No longer a minor.&quot;);
      • }
      • else
      • {
      • System.out.println(&quot;Not eligible to vote.&quot;);
      • System.out.println(&quot;Still a minor.&quot;);
      • }
      Java Programming: From Problem Analysis to Program Design, 5e
    • 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 if…else statements
      • May take longer to evaluate
      Java Programming: From Problem Analysis to Program Design, 5e
    • Multiple Selection: Nested if (continued) Java Programming: From Problem Analysis to Program Design, 5e
    • 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:
    • Multiple Selection: Nested if (continued) Java Programming: From Problem Analysis to Program Design, 5e
    • Multiple Selection: Nested if (continued) Java Programming: From Problem Analysis to Program Design, 5e
    • Java Programming: From Problem Analysis to Program Design, 5e
    • Java Programming: From Problem Analysis to Program Design, 5e
      • 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
    • Short-Circuit Evaluation (continued) Java Programming: From Problem Analysis to Program Design, 5e
    • Java Programming: From Problem Analysis to Program Design, 5e
    • Java Programming: From Problem Analysis to Program Design, 5e
    • Java Programming: From Problem Analysis to Program Design, 5e
    • 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 .
      • Then x and y are equal if the absolute value of (x – y) is less than 0.000001 . To find the absolute value, you can use the function Math.abs of the class Math , as shown in the program.
      • Therefore, the expression Math.abs(x – y) < 0.000001 determines whether the absolute value of (x – y) is less than 0.000001.
    • Conditional (? :) Operator
      • Ternary operator
      • Syntax
      • expression1 ? expression2 : expression3
      • If expression1 = 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
    • Java Programming: From Problem Analysis to Program Design, 5e
    • Java Programming: From Problem Analysis to Program Design, 5e
    • Java Programming: From Problem Analysis to Program Design, 5e
    • Java Programming: From Problem Analysis to Program Design, 5e
    • switch Structures Java Programming: From Problem Analysis to Program Design, 5e
    • switch Structures (continued) Java Programming: From Problem Analysis to Program Design, 5e
      • In Java, switch , case , break , and default are reserved words
      • In a switch structure, 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 word case
      • The expression is usually an identifier
      • The value of the identifier or the expression can be only of type int , byte , short , or char
    • switch Structures (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 particular case value must appear only once
      • One or more statements may follow a case label, so you do not need to use braces to turn multiple statements into a single compound statement
    • switch Structures (continued) Java Programming: From Problem Analysis to Program Design, 5e
      • The break statement may or may not appear after each statements1 , statements2 , ..., statementsn
      • A switch structure may or may not have the default label
    • switch Structures (continued) Java Programming: From Problem Analysis to Program Design, 5e
    • switch Structures (continued) Java Programming: From Problem Analysis to Program Design, 5e
      • Example 4-20
      • switch (grade)
      • {
      • case 'A':
      • System.out.println(&quot;The grade is A.&quot;);
      • break ;
      • case 'B':
      • System.out.println(&quot;The grade is B.&quot;);
      • break ;
      • case 'C':
      • System.out.println(&quot;The grade is C.&quot;);
      • break ;
      switch Structures (continued) Java Programming: From Problem Analysis to Program Design, 5e
      • case 'D':
      • System.out.println(&quot;The grade is D.&quot;);
      • break ;
      • case 'F':
      • System.out.println(&quot;The grade is F.&quot;);
      • break ;
      • default :
      • System.out.println(&quot;The grade is invalid.&quot;);
      • }
      switch Structures (continued) Java Programming: From Problem Analysis to Program Design, 5e
    • Java Programming: From Problem Analysis to Program Design, 5e
    • Java Programming: From Problem Analysis to Program Design, 5e
    • Java Programming: From Problem Analysis to Program Design, 5e
    • Java Programming: From Problem Analysis to Program Design, 5e To output results correctly, the switch structure must include a break statement after each println statement, except the last println statement.
    • Programming Example: Cable Company Billing
      • Input: customer’s account number, customer code, number of premium channels to which customer subscribes, number of basic service connections (in case of business customers)
      • Output: customer’s account number and the billing amount
      Java Programming: From Problem Analysis to Program Design, 5e
    • Programming Example: Cable Company Billing (continued)
      • Solution
        • Prompt user for information
        • Use switch statements based on customer’s 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
    • Comparing Strings
      • class String
        • Method compareTo
        • Method equals
      • Given string str1 and str2
      Java Programming: From Problem Analysis to Program Design, 5e
    • Comparing Strings (continued)
      • String str1 = &quot;Hello&quot;;
      • String str2 = &quot;Hi&quot;;
      • String str3 = &quot;Air&quot;;
      • String str4 = &quot;Bill&quot;;
      • String str5 = &quot;Bigger&quot;;
      Java Programming: From Problem Analysis to Program Design, 5e
    • Comparing Strings (continued) Java Programming: From Problem Analysis to Program Design, 5e
    • Comparing Strings (continued) Java Programming: From Problem Analysis to Program Design, 5e
    • Chapter Summary
      • Control structures are used to process programs
      • Logical expressions and order of precedence of operators are used in expressions
      • If statements
      • if … else statements
      • switch structures
      • Proper syntax for using control statements
      • Compare strings
      Java Programming: From Problem Analysis to Program Design, 5e