1. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 1 Chapter 1 Introduction to Computers, Programs, and Java

2. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 2 What is a Computer? A computer consists of a CPU, memory, hard disk, floppy disk, monitor, printer, and communication devices.

3. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 3 How Data is Stored? Data of various kinds, such as numbers, characters, and strings, are encoded as a series of bits (zeros and ones). Computers use zeros and ones because digital devices have two stable states, which are referred to as zero and one by convention. The programmers need not to be concerned about the encoding and decoding of data, which is performed automatically by the system based on the encoding scheme. The encoding scheme varies. For example, character ‘J’ is represented by 01001010 in one byte. A small number such as three can be stored in a single byte. If computer needs to store a large number that cannot fit into a single byte, it uses a number of adjacent bytes. No two data can share or split a same byte. A byte is the minimum storage unit.

4. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 4 Programs Computer programs, known as software, are instructions to the computer. You tell a computer what to do through programs. Without programs, a computer is an empty machine. Computers do not understand human languages, so you need to use computer languages to communicate with them. Programs are written using programming languages.

5. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 5 Programming Languages Machine Language Assembly Language High-Level Language Machine language is a set of primitive instructions built into every computer. The instructions are in the form of binary code, so you have to enter binary codes for various instructions. Program with native machine language is a tedious process. Moreover the programs are highly difficult to read and modify. For example, to add two numbers, you might write an instruction in binary like this: 1101101010011010

6. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 6 Programming Languages Machine Language Assembly Language High-Level Language Assembly languages were developed to make programming easy. Since the computer cannot understand assembly language, however, a program called assembler is used to convert assembly language programs into machine code. For example, to add two numbers, you might write an instruction in assembly code like this: ADDF3 R1, R2, R3

7. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 7 Programming Languages Machine Language Assembly Language High-Level Language The high-level languages are English-like and easy to learn and program. For example, the following is a high-level language statement that computes the area of a circle with radius 5: area = 5 * 5 * 3.1415;

8. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 8 Compiling Source Code A program written in a high-level language is called a source program. Since a computer cannot understand a source program. Program called a compiler is used to translate the source program into a machine language program called an object program. The object program is often then linked with other supporting library code before the object can be executed on the machine.

9. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 9 Compiling Java Source Code You can port a source program to any machine with appropriate compilers. The source program must be recompiled, however, because the object program can only run on a specific machine. Nowadays computers are networked to work together. Java was designed to run object programs on any platform. With Java, you write the program once, and compile the source program into a special type of object code, known as bytecode. The bytecode can then run on any computer with a Java Virtual Machine, as shown below. Java Virtual Machine is a software that interprets Java bytecode.

10. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 10 Number Systems 0, 1 0, 1, 2, 3, 4, 5, 6, 7 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F binary octal decimal hexdecimal

11. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 11 Hexadecimal  Binary 0000 0 0 0001 1 1 0010 2 2 0011 3 3 0100 4 4 0101 5 5 0110 6 6 0111 7 7 1000 8 8 1001 9 9 1010 A 10 1011 B 11 1100 C 12 1101 D 13 1110 E 14 1111 F 15 Binary Hex Decimal To convert a hexadecimal number to a binary number, simply convert each digit in the hexadecimal number into a four-digit binary number. To convert a binary number to a hexadecimal, convert every four binary digits from right to left in the binary number into a hexadecimal number. For example,

12. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 12 Why Java? The answer is that Java enables users to develop and deploy applications on the Internet for servers, desktop computers, and small hand-held devices. The future of computing is being profoundly influenced by the Internet, and Java promises to remain a big part of that future. Java is the Internet programming language. F Java is a general purpose programming language. F Java is the Internet programming language.

13. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 13 Java, Web, and Beyond F Java can be used to develop Web applications. F Java Applets F Java Web Applications F Java can also be used to develop applications for hand-held devices such as Palm and cell phones

14. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 14 Java’s History F James Gosling and Sun Microsystems F Oak F Java, May 20, 1995, Sun World F HotJava –The first Java-enabled Web browser F Early History Website: http://java.sun.com/features/1998/05/birthday.html

15. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 15 Characteristics of Java F Java Is Simple F Java Is Object-Oriented F Java Is Distributed F Java Is Interpreted F Java Is Robust F Java Is Secure F Java Is Architecture-Neutral F Java Is Portable F Java's Performance F Java Is Multithreaded F Java Is Dynamic Companion Website www.cs.armstrong.edu/liang/intro6e/JavaCharacteristics.pdf

16. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 16 JDK Versions F JDK 1.02 (1995) F JDK 1.1 (1996) F JDK 1.2 (1998) F JDK 1.3 (2000) F JDK 1.4 (2002) F JDK 1.5 (2004) a. k. a. JDK 5 or Java 5 F JDK 1.6 (2006) a. k. a. JDK 6 or Java 6

17. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 17 JDK Editions F Java Standard Edition (J2SE) – J2SE can be used to develop client-side standalone applications or applets. F Java Enterprise Edition (J2EE) – J2EE can be used to develop server-side applications such as Java servlets and Java ServerPages. F Java Micro Edition (J2ME). – J2ME can be used to develop applications for mobile devices such as cell phones. This book uses J2SE to introduce Java programming.

18. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 18 A Simple Java Program //This program prints Welcome to Java! public class Welcome { public static void main(String[] args) { System.out.println("Welcome to Java!"); } Run Welcome Listing 1.1

19. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 19 Creating, Compiling, and Running Programs

20. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 20 Compiling and Running Java from the Command Window F Set path to JDK bin directory –set path=c:\Program Files\java\jdk1.6.0\bin F Set classpath to include the current directory –set classpath=. F Compile –javac Welcome.java F Run –java Welcome Companion Website

21. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 21 Compiling and Running Java from TextPad F See Supplement II.A on the Website for details Companion Website

22. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 22 Anatomy of a Java Program F Comments F Package F Reserved words F Modifiers F Statements F Blocks F Classes F Methods F The main method

23. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 23 Comments Line comment: A line comment is preceded by two slashes (//) in a line. Paragraph comment: A paragraph comment is enclosed between /* and */ in one or multiple lines. javadoc comment: javadoc comments begin with /** and end with */. They are used for documenting classes, data, and methods. They can be extracted into an HTML file using JDK's javadoc command. Three types of comments in Java.

24. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 24 Package The second line in the program (package chapter1;) specifies a package name, chapter1, for the class Welcome. Forte compiles the source code in Welcome.java, generates Welcome.class, and stores Welcome.class in the chapter1 folder.

25. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 25 Reserved Words Reserved words or keywords are words that have a specific meaning to the compiler and cannot be used for other purposes in the program. For example, when the compiler sees the word class, it understands that the word after class is the name for the class. Other reserved words in Listing 1.1 are public, static, and void. Their use will be introduced later in the book.

26. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 26 Modifiers Java uses certain reserved words called modifiers that specify the properties of the data, methods, and classes and how they can be used. Examples of modifiers are public and static. Other modifiers are private, final, abstract, and protected. A public datum, method, or class can be accessed by other programs. A private datum or method cannot be accessed by other programs. Modifiers are discussed in Chapter 6, “Objects and Classes.”

27. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 27 Statements A statement represents an action or a sequence of actions. The statement System.out.println("Welcome to Java!") in the program in Listing 1.1 is a statement to display the greeting "Welcome to Java!" Every statement in Java ends with a semicolon (;).

28. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 28 Blocks A pair of braces in a program forms a block that groups components of a program.

29. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 29 Classes The class is the essential Java construct. A class is a template or blueprint for objects. To program in Java, you must understand classes and be able to write and use them. The mystery of the class will continue to be unveiled throughout this book. For now, though, understand that a program is defined by using one or more classes.

30. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 30 Methods What is System.out.println? It is a method: a collection of statements that performs a sequence of operations to display a message on the console. It can be used even without fully understanding the details of how it works. It is used by invoking a statement with a string argument. The string argument is enclosed within parentheses. In this case, the argument is "Welcome to Java!" You can call the same println method with a different argument to print a different message.

31. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 31 main Method The main method provides the control of program flow. The Java interpreter executes the application by invoking the main method. The main method looks like this: public static void main(String[] args) { // Statements; }

32. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 32 Chapter 2 Elementary Programming

33. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 33 Motivations In the preceding chapter, you learned how to create, compile, and run a Java program. Starting from this chapter, you will learn how to solve practical problems programmatically. Through these problems, you will learn Java primitive data types and related subjects, such as variables, constants, data types, operators, expressions, and input and output.

34. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 34 Introducing Programming with an Example Listing 2.1 Computing the Area of a Circle This program computes the area of the circle. ComputeArea Run

35. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 35 Trace a Program Execution public class ComputeArea { /** Main method */ public static void main(String[] args) { double radius; double area; // Assign a radius radius = 20; // Compute area area = radius * radius * 3.14159; // Display results System.out.println("The area for the circle of radius " + radius + " is " + area); } no value radius memory no value area allocate memory for area animation

36. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 36 Trace a Program Execution public class ComputeArea { /** Main method */ public static void main(String[] args) { double radius; double area; // Assign a radius radius = 20; // Compute area area = radius * radius * 3.14159; // Display results System.out.println("The area for the circle of radius " + radius + " is " + area); } 20 radius memory 1256.636 area print a message to the console animation

37. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 37 Identifiers F An identifier is a sequence of characters that consist of letters, digits, underscores (_), and dollar signs ($). F An identifier must start with a letter, an underscore (_), or a dollar sign ($). It cannot start with a digit. –An identifier cannot be a reserved word. (See Appendix A, “Java Keywords,” for a list of reserved words).  An identifier cannot be true, false, or null. F An identifier can be of any length.

38. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 38 Declaring Variables int x; // Declare x to be an // integer variable; double radius; // Declare radius to // be a double variable; char a; // Declare a to be a // character variable;

39. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 39 Assignment Statements x = 1; // Assign 1 to x; radius = 1.0; // Assign 1.0 to radius; a = 'A'; // Assign 'A' to a;

40. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 40 Declaring and Initializing in One Step F int x = 1; F double d = 1.4;

41. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 41 Constants final datatype CONSTANTNAME = VALUE; final double PI = 3.14159; final int SIZE = 3;

42. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 42 Numerical Data Types

43. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 43 Numeric Operators

44. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 44 Integer Division +, -, *, /, and % 5 / 2 yields an integer 2. 5.0 / 2 yields a double value 2.5 5 % 2 yields 1 (the remainder of the division)

45. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 45 NOTE Calculations involving floating-point numbers are approximated because these numbers are not stored with complete accuracy. For example, System.out.println(1.0 - 0.1 - 0.1 - 0.1 - 0.1 - 0.1); displays 0.5000000000000001, not 0.5, and System.out.println(1.0 - 0.9); displays 0.09999999999999998, not 0.1. Integers are stored precisely. Therefore, calculations with integers yield a precise integer result.

46. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 46 Number Literals A literal is a constant value that appears directly in the program. For example, 34, 1,000,000, and 5.0 are literals in the following statements: int i = 34; long x = 1000000; double d = 5.0;

47. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 47 Integer Literals An integer literal can be assigned to an integer variable as long as it can fit into the variable. A compilation error would occur if the literal were too large for the variable to hold. For example, the statement byte b = 1000 would cause a compilation error, because 1000 cannot be stored in a variable of the byte type. An integer literal is assumed to be of the int type, whose value is between -2 31 (-2147483648) to 2 31 –1 (2147483647). To denote an integer literal of the long type, append it with the letter L or l. L is preferred because l (lowercase L) can easily be confused with 1 (the digit one).

48. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 48 Floating-Point Literals Floating-point literals are written with a decimal point. By default, a floating-point literal is treated as a double type value. For example, 5.0 is considered a double value, not a float value. You can make a number a float by appending the letter f or F, and make a number a double by appending the letter d or D. For example, you can use 100.2f or 100.2F for a float number, and 100.2d or 100.2D for a double number.

49. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 49 Shortcut Assignment Operators OperatorExampleEquivalent +=i += 8i = i + 8 -=f -= 8.0f = f - 8.0 *=i *= 8i = i * 8 /=i /= 8i = i / 8 %=i %= 8i = i % 8

50. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 50 Increment and Decrement Operators OperatorNameDescription ++varpreincrementThe expression (++var) increments var by 1 and evaluates to the new value in var after the increment. var++postincrementThe expression (var++) evaluates to the original value in var and increments var by 1. --varpredecrementThe expression (--var) decrements var by 1 and evaluates to the new value in var after the decrement. var--postdecrement The expression (var--) evaluates to the original value in var and decrements var by 1.

51. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 51 Increment and Decrement Operators, cont.

52. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 52 Numeric Type Conversion Consider the following statements: byte i = 100; long k = i * 3 + 4; double d = i * 3.1 + k / 2;

53. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 53 Conversion Rules When performing a binary operation involving two operands of different types, Java automatically converts the operand based on the following rules: 1. If one of the operands is double, the other is converted into double. 2. Otherwise, if one of the operands is float, the other is converted into float. 3. Otherwise, if one of the operands is long, the other is converted into long. 4. Otherwise, both operands are converted into int.

54. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 54 Type Casting Implicit casting double d = 3; (type widening) Explicit casting int i = (int)3.0; (type narrowing) int i = (int)3.9; (Fraction part is truncated) What is wrong?int x = 5 / 2.0;

55. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 55 Unicode Format Java characters use Unicode, a 16-bit encoding scheme established by the Unicode Consortium to support the interchange, processing, and display of written texts in the world’s diverse languages. Unicode takes two bytes, preceded by \u, expressed in four hexadecimal numbers that run from '\u0000' to '\uFFFF'. So, Unicode can represent 65535 + 1 characters. Unicode \u03b1 \u03b2 \u03b3 for three Greek letters

56. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 56 Escape Sequences for Special Characters Description Escape Sequence Unicode Backspace \b\u0008 Tab \t\u0009 Linefeed \n\u000A Carriage return \r\u000D Backslash \\\u005C Single Quote \ ' \u0027 Double Quote \ " \u0022

57. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 57 Casting between char and Numeric Types int i = ' a ' ; // Same as int i = (int) ' a ' ; char c = 97; // Same as char c = (char)97;

58. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 58 The String Type The char type only represents one character. To represent a string of characters, use the data type called String. For example, String message = "Welcome to Java"; String is actually a predefined class in the Java library just like the System class and JOptionPane class. The String type is not a primitive type. It is known as a reference type. Any Java class can be used as a reference type for a variable. Reference data types will be thoroughly discussed in Chapter 7, “Objects and Classes.” For the time being, you just need to know how to declare a String variable, how to assign a string to the variable, and how to concatenate strings.

59. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 59 String Concatenation // Three strings are concatenated String message = "Welcome " + "to " + "Java"; // String Chapter is concatenated with number 2 String s = "Chapter" + 2; // s becomes Chapter2 // String Supplement is concatenated with character B String s1 = "Supplement" + 'B'; // s becomes SupplementB

60. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 60 Getting Input Using Scanner 1. Create a Scanner object Scanner scanner = new Scanner(System.in); 2. Use the methods next(), nextByte(), nextShort(), nextInt(), nextLong(), nextFloat(), nextDouble(), or nextBoolean() to obtain to a string, byte, short, int, long, float, double, or boolean value. For example, System.out.print("Enter a double value: "); Scanner scanner = new Scanner(System.in); double d = scanner.nextDouble(); TestScannerRun

61. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 61 Appropriate Comments Include a summary at the beginning of the program to explain what the program does, its key features, its supporting data structures, and any unique techniques it uses. Include your name, class section, instructor, date, and a brief description at the beginning of the program.

62. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 62 Naming Conventions F Choose meaningful and descriptive names. F Variables and method names: –Use lowercase. If the name consists of several words, concatenate all in one, use lowercase for the first word, and capitalize the first letter of each subsequent word in the name. For example, the variables radius and area, and the method computeArea.

63. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 63 Naming Conventions, cont.  Class names: –Capitalize the first letter of each word in the name. For example, the class name ComputeArea. F Constants: –Capitalize all letters in constants, and use underscores to connect words. For example, the constant PI and MAX_VALUE

64. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 64 Proper Indentation and Spacing  Indentation –Indent two spaces. F Spacing –Use blank line to separate segments of the code.

65. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 65 Block Styles Use end-of-line style for braces.

66. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 66 Programming Errors F Syntax Errors –Detected by the compiler F Runtime Errors –Causes the program to abort F Logic Errors –Produces incorrect result

67. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 67 Syntax Errors public class ShowSyntaxErrors { public static void main(String[] args) { i = 30; System.out.println(i + 4); }

68. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 68 Runtime Errors public class ShowRuntimeErrors { public static void main(String[] args) { int i = 1 / 0; }

69. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 69 Logic Errors public class ShowTwoLogicErrors { public static void main(String[] args) { // Compute the square of a number int number = 121; int square = number + number; // Display the result System.out.println("The square of number" + number + " is " + square); // Terminate the program System.exit(0); }

70. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 70 Debugging Logic errors are called bugs. The process of finding and correcting errors is called debugging. A common approach to debugging is to use a combination of methods to narrow down to the part of the program where the bug is located. You can hand-trace the program (i.e., catch errors by reading the program), or you can insert print statements in order to show the values of the variables or the execution flow of the program. This approach might work for a short, simple program. But for a large, complex program, the most effective approach for debugging is to use a debugger utility.

71. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 71 Debugger Debugger is a program that facilitates debugging. You can use a debugger to F Execute a single statement at a time. F Trace into or stepping over a method. F Set breakpoints. F Display variables. F Display call stack. F Modify variables.

72. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 72 Getting Input from Input Dialog Boxes String input = JOptionPane.showInputDialog( "Enter an input");

73. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 73 Getting Input from Input Dialog Boxes String string = JOptionPane.showInputDialog( null, “Prompting Message”, “Dialog Title”, JOptionPane.QUESTION_MESSAGE);

74. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 74 Converting Strings to Integers The input returned from the input dialog box is a string. If you enter a numeric value such as 123, it returns “123”. To obtain the input as a number, you have to convert a string into a number. To convert a string into an int value, you can use the static parseInt method in the Integer class as follows: int intValue = Integer.parseInt(intString); where intString is a numeric string such as “123”.

75. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671 75 Converting Strings to Doubles To convert a string into a double value, you can use the static parseDouble method in the Double class as follows: double doubleValue =Double.parseDouble(doubleString); where doubleString is a numeric string such as “123.45”.