Java with BlueJ, 2016a

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20 CHAPTER 2. BASICS memory that holds a value that a program can use and change as it executes. primitive types The Java programming language requires us to declare the type of data to be associated with a variable. Java makes a distinction between primitive data types and other data types defined via classes. In the Java class libraries there are many pre-defined classes, for example: String and System. The Java language contains eight primitive data types: byte, short, int, long, float, double, char and boolean: • byte, short, int, andlong are used for cases where the data is to be treated as whole numbers (numbers without a fractional component). For example, 33, 498, -100 are whole numbers. These data types differ with regards to the magnitude of number they can represent. • float and double are used for cases where the data is numeric and where one expects values to have a fractional component such as: 101.5, 26.334, -55.5. When written we show them with a decimal point. Again, these two types differ with regards to size in terms of the number of significant digits and in the magnitude of the number they can represent. • char is used when there are individual characters to be handled. Examples of individual characters are ’a’, ’b’, ’q’, ’$’. Values are enclosed in single quotes. • boolean is used when the situation requires one to work with logical values of true and false. In a Java program these values are written just as we do in English: true, false. A Java programmer declares a variable in a declaration statement, and then uses the variable name later in a program to assign a value, to alter the current value, and to reference the value currently stored. Two example programs follow; in Listing 2.1 the program defines and uses a variable, and in Listing 2.2 the program alters the value stored in a variable. In Listing 2.1 note the following: • In line 10 an int variable named i is declared, • In line 11 the value 14 is assigned to i (that is, the value 14 is stored in the memory location reserved for i), • Line 12 displays the value of i
2.2. VARIABLES 21 Listing 2.1: Using a variable 1 /** 2 * This Java class declares 3 * an int variable named i, 4 * assigns the value 14 to i, 5 * and displays i. 6 */ 7 public class Variable 8 { 9 public static void main(String[] args){ 10 int i; 11 i = 14; 12 System.out.println(i); 13 } 14 } Listing 2.2 starts off like Listing 2.1 but modifies the value of i to 30 in line 13 just before it is displayed for the second time. This program changes the value associated with the variable. Listing 2.2: Changing the value stored in a variable 1 /** 2 * This Java class declares 3 * an int variable named i, 4 * assigns it a value and then 5 * changes its value. 6 */ 7 public class VariableChanged 8 { 9 public static void main(String[] args){ 10 int i; 11 i = 14; 12 System.out.println(i); 13 i = 30; 14 System.out.println(i); 15 } 16 }
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: Chapter 2 Basics This chapter cover
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
Page 33 and 34: 2.3. PRIMITIVE DATA TYPES 33 10 int
Page 35 and 36: 2.3. PRIMITIVE DATA TYPES 35 where
Page 37 and 38: 2.3. PRIMITIVE DATA TYPES 37 to kno
Page 39 and 40: 2.3. PRIMITIVE DATA TYPES 39 9 // D
Page 41 and 42: 2.3. PRIMITIVE DATA TYPES 41 use in
Page 43 and 44: 2.4. OPERATORS 43 2.4 Operators We
Page 45 and 46: 2.4. OPERATORS 45 odd statement to
Page 47 and 48: 2.5. THE STRING CLASS 47 Since text
Page 49 and 50: 2.5. THE STRING CLASS 49 name of th
Page 51 and 52: 2.5. THE STRING CLASS 51 Example, d
Page 53 and 54: 2.5. THE STRING CLASS 53 Exercises
Page 55 and 56: 2.6. OUTPUT 55 12 // Each time prin
Page 57 and 58: 2.6. OUTPUT 57 Test your program wi
Page 59 and 60: 2.6. OUTPUT 59 • Lines 14 and 15
Page 61 and 62: 2.7. INPUT 61 2.7 Input We examine
Page 63 and 64: 2.7. INPUT 63 Figure 2.8: Terminal
Page 65 and 66: 2.7. INPUT 65 2.7.2 The JOptionPane
Page 67 and 68: Chapter 3 Control Structures Progra
Page 69 and 70: 3.2. WHILE 69 A logical expression
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3.2. WHILE 71 Figure 3.1: Output fr
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3.2. WHILE 73 An example of output
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3.2. WHILE 75 25 } 26 } Figure 3.2:
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3.2. WHILE 77 Autoincrement Because
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3.3. IF 79 Example 1 Suppose one ne
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3.3. IF 81 Exercises 15. Write a pr
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3.3. IF 83 9 { 10 public static voi
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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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