Java with BlueJ, 2016a

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36 CHAPTER 2. BASICS 2.3.4 boolean Data Type The boolean type has two values: true and false. We will see that the boolean type can be useful when we discuss control structures in the next chapter. There are three operators defined for booleans: and, or and not represented in Java as &&, ||, and! respectively. && and || are binary operators where the operator appears between the two operands; ! is a unary operator that precedes its operand. Boolean operators operator in Java meaning AND && Evaluates to true if and only if both operands are true; evaluates to false otherwise. OR || Evaluates to true if at least one operand is true; evaluates to false if both operands are false. NOT ! NOT: negates the operand. Three truth tables below show the results for Boolean operators for all possible values of their operands. Boolean operation of AND a b a && b true true true false true false true false false false false false Boolean operation of OR a b a || b true true true false true true true false true false false false Boolean operation of NOT a ! a true false false true The following table gives some example boolean expressions. The last 3 examples are complex expressions. To understand those evaluations we need
2.3. PRIMITIVE DATA TYPES 37 to know Java rules for evaluating these expressions (discussed in the notes below). Examples boolean x, y, z; x=false; y=true; z=true; example result 1 y true 2 y && z true 3 x || y true 4 !x true 5 x && y || ! z false 6 ! x || y true 7 ! (x || y) false A Boolean expression may have multiple operators. Consider example 5 from above, x && y || ! z We need to be clear on how Java evaluates such an expression. Java assigns priorities to these Boolean operators: ! is highest, followed by &&, followed by ||. Higher priority operators are evaluated before lower priority operators. So, for the above expression !z is evaluated first yielding false. So now the expression effectively becomes: x && y || false As && has higher priority than || it is evaluated next yielding false. So now the expression effectively becomes: false || false which evaluates to false. Java allows sub-expressions; these are expressions enclosed in parentheses. A sub-expression is evaluated before the expression of which it is a part, and that value is substituted in its place. Consider examples 6 and 7 from above. They are the same except for the use of parentheses. In example 6: ! x || y the ! is evaluated first and the expression effectively becomes: true || y which evaluates to true. In example 7: ! (x || y) the sub-expression (x || y) is evaluated first, and then ! is evaluated. Since x||y evaluates to true, the result for the expression is false. priorities sub-expressions
Page 1 and 2: Java with BlueJ Part I Ron McFadyen
Page 3 and 4: To Callum 3
Page 5 and 6: Contents 1 Introduction 9 1.1 Java,
Page 7 and 8: Preface This book is Part I of a tw
Page 9 and 10: Chapter 1 Introduction This book is
Page 11 and 12: 1.2. THE JAVA COMPILER AND THE JAVA
Page 13 and 14: 1.4. A FIRST PROGRAM 13 1.4 A First
Page 15 and 16: 1.5. USING BLUEJ TO RUN HELLOWORLD
Page 17 and 18: 1.5. USING BLUEJ TO RUN HELLOWORLD
Page 19 and 20: Chapter 2 Basics This chapter cover
Page 21 and 22: 2.2. VARIABLES 21 Listing 2.1: Usin
Page 23 and 24: 2.3. PRIMITIVE DATA TYPES 23 Exerci
Page 25 and 26: 2.3. PRIMITIVE DATA TYPES 25 Defaul
Page 27 and 28: 2.3. PRIMITIVE DATA TYPES 27 14 Sys
Page 29 and 30: 2.3. PRIMITIVE DATA TYPES 29 2.3.3
Page 31 and 32: 2.3. PRIMITIVE DATA TYPES 31 Exampl
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Page 53 and 54: 2.5. THE STRING CLASS 53 Exercises
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Page 61 and 62: 2.7. INPUT 61 2.7 Input We examine
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Page 65 and 66: 2.7. INPUT 65 2.7.2 The JOptionPane
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Page 85 and 86: 3.3. IF 85 Listing 3.6: Using an if
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3.3. IF 87 the indentation. Each of
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3.4. FOR 89 3.4 for The for stateme
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3.4. FOR 91 Example 1 Below we use
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3.4. FOR 93 Table 3.1: Process indi
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3.4. FOR 95 Example 4 The program i
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3.4. FOR 97 Example 5 In this examp
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3.4. FOR 99 . . . Step 2, formattin
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3.4. FOR 101 Exercises 20. Modify t
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3.4. FOR 103 34. Modify the previou
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3.5. DO ...WHILE 105 Example 1 Let
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3.5. DO ...WHILE 107 Listing 3.16:
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3.6. SWITCH 109 3.6 switch The swit
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3.6. SWITCH 111 Example 1 Previousl
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3.6. SWITCH 113 Exercises 39. Write
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Chapter 4 Classes in the Java Class
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4.1. RANDOM 117 Example 2 Consider
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4.1. RANDOM 119 Exercises 1. Modify
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4.2. CHARACTER 121 Example 1 Ifthed
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4.2. CHARACTER 123 Example 2 The Ch
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4.2. CHARACTER 125 Below is the out
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4.3. SCANNER 127 4.3 Scanner Previo
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4.3. SCANNER 129 Note that the abov
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4.3. SCANNER 131
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4.3. SCANNER 133 Exercises 11. Modi
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4.4. MATH 135 The Math Class Fields
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4.5. INTEGER 137 4.5 Integer The In
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4.5. INTEGER 139 Listing 4.9: Using
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Chapter 5 ArrayLists There are seve
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143 The enhanced for Thereisavariat
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145 Example 2 The contains() method
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147 20 people.add(new Random()); 21
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Chapter 6 One-Dimensional Arrays Th
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6.1. INITIALIZING ARRAYS 151 6.1 In
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6.3. THE ENHANCED FOR 153 6.3 The e
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6.4. PASSING STRING VALUES INTO MAI
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6.5. PARALLEL ARRAYS 157 18 } This
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6.6. PARTIALLY FILLED ARRAYS 159 Th
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6.7. ARRAY UTILITIES IN JAVA CLASS
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6.7. ARRAY UTILITIES IN JAVA CLASS
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Chapter 7 Designing Java Classes Up
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7.1. USING MULTIPLE CLASSES 167 7.1
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7.2. FIELDS 169 Figure 7.2: Class d
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7.3. METHODS 171 7.3 Methods A meth
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7.3. METHODS 173 Calling the other
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7.3. METHODS 175 void methods Somet
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7.4. CONSTRUCTORS 177 10 private St
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7.4. CONSTRUCTORS 179 Using constru
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7.5. VISIBILITY SPECIFICATIONS: PUB
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7.7. ASSOCIATIONS 183 7.7 Associati
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7.7. ASSOCIATIONS 185 Notice that t
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7.7. ASSOCIATIONS 187 Now reconside
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7.8. REUSING CODE 189 24 } The outp
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7.9. PARAMETER LISTS AND ARGUMENTS
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7.10. VARARGS: A VARIABLE NUMBER OF
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7.11. CODE LISTINGS: STUDENT, SUBJE
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Chapter 8 A Brief Introduction to G
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8.1. BRIEF INTRODUCTION TO SIMPLE G
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