Oct. 3 fixup - Here are notes and codes in the proper order that they should be.

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1 Oct. 3 fixup - Here are notes and codes in the proper order that they should be. The boolean Data Type The boolean data type allows you to create variables that may hold one of two possible values: true or false. Code Listing 2-13 demonstrates the declaration and assign;: a boolean variable (TrueFalse. java) //A program for demonstrating boolean variables public class TrueFalse public static void main(string[] args) boolean bool; bool = true; System.out.println(bool); bool = false; System.out.println(bool); Program Output: true false Variables of the boolean data type are useful for evaluating conditions that are either true or false. You will not be using them until Chapter 3, however, so for now just remember the following things: boolean variables may only hold the values true or false. The contents of a boolean variable may not be copied to a variable of any type other than boolean. The char Data Type The char data type is used to store characters. A variable of the char data type can hold one character at a time. Character literals are enclosed in single quotation marks. The program in Code Listing 2-14 uses a char variable. The character literals 'A and 'B' are assigned to the variable.

2 2.14 (Letters. java) //This program demonstrates the char data type. public class Letters public static void main(string[] args) char letter; letter = 'A'; System.out.println(letter); letter = 'B'; System.out.println(letter); Program Output A B It is important that you do not confuse character literals with string literals, which are enclosed in double quotation marks. String literals cannot be assigned to char variables. Unicode Characters are internally represented by numbers. Each printable character, as well as many non-printable characters, is assigned a unique number. Java uses Unicode, which is a set of numbers that are used as codes for representing characters. Each Unicode number requires two bytes of memory, so char variables occupy two bytes. When a character is stored in memory it is actually the numeric code that is stored. When the computer is instructed to print the value on the screen, it displays the character that corresponds with the numeric code. You may want to refer to Appendix B on the Student CD which shows a portion of the Unicode character set. Notice that the number 65 is the code for A, 66 is the code for B, and so on. Code Listing 2-15 demonstrates that when you work with characters, you are actually working with numbers.

3 Code Listing 2-15 (Letters2) // This program demonstrates the close relationship between // characters and integers. public class Letters2! public static void main(string[] args)!! char letter;!!!! letter = 65;!! System.out.println(letter);!! letter = 66;!! System.out.println(letter);! Variable Assignment and Initialization As you have already seen in several examples, a value is put into a variable with an assignment statement. For example, the following statement assigns the value 12 to the variable unitssold: unitssold = 12; The = symbol is called the assignment operator. Operators perform operations on data. The data that operators work with are called operands. The assignment operator has two operands. In the statement above, the operands are unitssold and 12. In an assignment statement, the name of the variable receiving the assignment must appear on the left side of the operator, and the value being assigned must appear on the right side. The following statement is incorrect: 12 = unitssold; // ERROR! The operand on the left side of the = operator must be a variable name. The operand on right side of the = symbol must be an expression that has a value. The assignment operator takes the value of the right operand and puts it in the variable identified by the left operand, Assuming that length and width are both int variables, the following code illustrates the the assignment operator's right operand may be a literal or a variable: length = 20; width = length;

4 It is important to note that the assignment operator only changes the contents of its operand. The second statement assigns the value of the length variable to the width variable. After the statement has executed, length still has the same value, 20. You may also assign values to variables as part of the declaration statement. This is known as initialization. Code Listing 2-16 shows how it is done. The variable declaration statement in this program is in line 7: int month = 2, days = 28; 2-16 (Initialize.java) // This program shows variable initialization public class Initialize! public static void main(string[] args)!! int month = 2, days = 28;!!!! System.out.println("Month " + month + " has " +!! days + " days.");!!!!!!! This statement declares the month variable and initializes it with the value 2, and declares the days variable and initializes it with the value 28. As you can see, this simplifies the program and reduces the number of statements that must be typed by the programmer. Here are examples of other declaration statements that perform initialization: double payrate = 25.52; float interestrate = 12.9F; char stockcode = 'D'; int customernum = 459; Of course, there are always variations on a theme. Java allows you to declare several variables and only initialize some of them. Here is an example of such a declaration: int flightnum = 89, traveltime, departure = 10, distance;

5 The variable flightnum is initialized to 89 and departure is initialized to 10. The traveltime distance variables remain uninitialized. WARNING! When a variable is declared inside a method, it must have a value stored in it before it can be used. If the compiler determines that the program might be using such a variable before a value has been stored in it, an error will occur. You can avoid this type of error by initializing the variable with a value. Variables Hold Only One Value at a Time Remember, a variable can hold only one value at a time. When you assign a new value to a variable, the new value takes the place of the variable's previous contents. For example, look at the following code. int x = 5; System.out.println(x); x = 99; System.out.println(x); In this code, the variable x is initialized with the value 5 and its contents are displayed. Then the variable is assigned the value 99. This value overwrites the value 5 that was previously stored there. The code will produce the following output: 5 99 Checkpoint 2.12 Which of the following are illegal variable names and why? x 99bottles july97 thesalesfigure ForFiscalYear 98 r&d grade_report 2.13 Is the variable name Sales the same as sales? Why or why not? 2.16 A program declares a float variable named number, and the following statement causes an error. What can be done to fix the error? number = 7.4;

6 2.17 What values can boolean variables hold? 2.18 Write statements that do the following: a) Declare a char variable named letter. b) Assign the letter A to the letter variable. c) Display the contents of the letter variable What are the Unicode codes for the characters 'C', 'F', and 'W'? (You may need to refer to Appendix B on the Student CD.) 2.20 Which is a character literal, 'B' or "B"? 2.21 What is wrong with the following statement? char letter = "Z";

7 The program in Code Listing 2-17 demonstrates some of these operators used in a simple payroll calculation. (Wages. java) //This program calculates hourly wages plus overtime. public class Wages public static void main(string[] args) double regularwages; // The calculated regular wages. double basepay = 61; // The base pay rate. double regularhours = 100; // The hours worked less overtime. double overtimewages; // Overtime wages double overtimepay = 50; // Overtime pay rate double overtimehours = 200; // Overtime hours worked double totalwages; // Total wages regularwages = basepay * regularhours; overtimewages = overtimepay * overtimehours; totalwages = regularwages + overtimewages; System.out.println("Wages for this week are $" + totalwages); Program Output: Wages for this week are $