Chapter 2 Elementary Programming

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

Objectives • To write Java programs to perform simple calculations (§2.2). • To use identifiers to name variables, constants, methods, and classes (§2.3). • To use variables to store data (§§2.4-2.5). • To program with assignment statements and assignment expressions (§2.5). • To use constants to store permanent data (§2.6). • To declare Java primitive data types: byte, short, int, long, float, double, and char (§§2.7 – 2.9). • To use Java operators to write numeric expressions (§§2.7–2.8). • To represent characters using the char type (§2.9). • To represent a string using the String type (§2.10). • To obtain input from the console using the Scanner class (§§2.11-2.12). • To become familiar with Java documentation, programming style, and naming conventions (§2.13). • To distinguish syntax errors, runtime errors, and logic errors (§2.14). • To debug logic errors (§2.15). • (GUI) To obtain input using the JOptionPane input dialog boxes (§2.16). Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

Path to Java Compiler path = C:\Program Files\Java\jdk1.6.0_16\bin set classpath=. Copy the above two lines and past into Notepad file and save as setJavaPath.bat From DOS window (Command Prompt) go to directory where you saved setJavaPath.bat From the command line enter setJavaPath Go to subdirectory where you have the java files. You should be able to compile and run the programs. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

Introducing Programming with an Example Listing 2.1 Computing the Area of a Circle public class ComputeArea { public static void main(String[] args) { double radius; // Declare radius double area; // Declare area radius = 20; // Assign a radius // Compute area area = radius * radius * 3.14159; // Display results System.out.println ("The area for the circle of radius " + radius + " is " + area); } } Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

animation 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); } } allocate memory for radius radius no value Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

animation 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); } } memory radius no value area no value allocate memory for area Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

animation 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); } } assign 20 to radius radius 20 area no value Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

animation 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); } } memory radius 20 area 1256.636 compute area and assign it to variable area Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

animation 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); } } memory radius 20 area 1256.636 print a message to the console Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

Identifiers • An identifier is a sequence of characters that consist of letters, digits, underscores (_), and dollar signs ($). • An identifier must start with a letter, an underscore (_), or a dollar sign ($). 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 betrue, false, or null. • An identifier can be of any length. • Java is case sensitive • Upper case letters are not the same as lower case letters • Examples • Name is not the same as name Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

Variables publicclass DisplayRadius { publicstaticvoid main(String[]args) { double radius; //Declare variable radius double area; //Declare variable area // Compute the first area radius = 1.0; //assign value to variable radius area = radius * radius * 3.14159; //compute value of area System.out.println("The area is " + area + " for radius " + radius); // Compute the second area radius = 2.0; //assign value to variable radius area = radius * radius * 3.14159; //compute value of area System.out.println("The area is " + area + " for radius "+radius); } } The area is 3.14159 for radius 1.0 The area is 12.56636 for radius 2.0 Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

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; • Declarations are used to • tell the compiler how much memory space is needed for the value that will be assigned to the variable • tell the compiler the type of data that will be referenced by that variable Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

Assignment Statements x = 1; // Assign 1 to x; radius = 1.0; // Assign 1.0 to radius; a = 'A'; // Assign 'A' to a; • Assignment statements • Assign a value to the variable • That value is stored in the memory location associated with that variable Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

Declaring and Initializing in One Step • int x = 1; • double d = 1.4; • In Jave, you can declare a variable and store a value in that variable in one statement • It is usually a good idea to initialize the variable when it is declared Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

Constants • Constant • Once a value is assigned it cannot be changed • final is the keyword used to declare a variable a constant • Format • final datatype CONSTANTNAME = VALUE; • Examples • final double PI = 3.14159; • final int SIZE = 3; • Note • Convention is to use all upper case letters for the name of the constant variable Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

TIP An excellent tool to demonstrate how numbers are stored in a computer was developed by Richard Rasala. You can access it at http://www.ccs.neu.edu/jpt/jpt_2_3/bitdisplay/applet.htm Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

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

Remainder Operator • Remainder is very useful in programming. • For example • an even number % 2 is always 0 • an odd number % 2 is always 1. • So you can use this property to determine whether a number is even or odd. • Suppose today is Saturday and you and your friends are going to meet in 10 days. What day is in 10 days? You can find that day is Tuesday using the following expression: Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

Problem: Displaying Time Write a program that obtains hours and minutes from seconds. publicclass DisplayTime { publicstaticvoid main(String[] args) { int seconds = 500; int minutes = seconds / 60; int remainingSeconds = seconds % 60; System.out.println(seconds + " seconds is " + minutes + " minutes and " + remainingSeconds + " seconds"); } } 500 seconds is 8 minutes and 20 seconds Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

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

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

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 • -231 (-2147483648) to 231–1 (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). Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

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

Scientific Notation • Floating-point literals can also be specified in scientific notation • For example, 1.23456e+2, same as 1.23456e2, is equivalent to 123.456, and 1.23456e-2 is equivalent to 0.0123456. • E (or e) represents an exponent and it can be either in lowercase or uppercase. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

Arithmetic Expressions is translated to (3+4*x)/5 – 10*(y-5)*(a+b+c)/x + 9*(4/x + (9+x)/y) Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

How to Evaluate an Expression Though Java has its own way to evaluate an expression behind the scene, the result of a Java expression and its corresponding arithmetic expression are the same. Therefore, you can safely apply the arithmetic rule for evaluating a Java expression. Appendix C, page 690, has a chart of operator precedence. We will cover this in detail in Chapter 3. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

Problem: Converting Temperatures Write a program that converts a Fahrenheit degree to Celsius using the formula: publicclass FahrenheitToCelsius { publicstaticvoid main(String[] args) { double fahrenheit = 435; // Say 100; double celsius = (5.0 / 9) * (fahrenheit - 32); System.out.println("Fahrenheit " + fahrenheit + " is " + celsius + " in Celsius"); } } Fahrenheit 435.0 is 223.88888888888889 in Celsius Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

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

Increment and Decrement Operators Operator Name Description ++var preincrement The expression (++var) increments var by 1 and evaluates to the new value in varafter the increment. var++ postincrement The expression (var++) evaluates to the original value in var and increments var by 1. --var predecrement The expression (--var) decrements var by 1 and evaluates to the new value in varafter the decrement. var-- postdecrement The expression (var--) evaluates to the original value in var and decrements var by 1. ++var and --var: performs the arithmetic operation first than uses the value. var++ and var– uses the value first than performs the arithmetic operation. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

Increment and Decrement Operators, cont. newNum will have the value 100, i will have the value 11 newNum will have the value 110, i will have the value 11 Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

Increment and Decrement Operators, cont. • Using increment and decrement operators makes expressions short, but it also makes them complex and difficult to read. • Avoid using these operators in expressions that modify multiple variables, or the same variable for multiple times such as this: int k = ++i + i. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

Assignment Expressions and Assignment Statements Prior to Java 2, all the expressions could be used as statements. Since Java 2, only the following types of expressions can be statements: variable op= expression; // Where op is +, -, *, /, or % ++variable; variable++; --variable; variable--; • Expressions perform operations on data and move data around. • All statements except blocks are terminated by a semicolon. Blocks are denoted by open and close curly braces. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

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

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

8-bits 16-bits 32-bits 64-bits 32-bits 64-bits 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; converts the 5 to 5.0, performs division to get 2.5 then tries to store a double in an int, but it won’t fit. You will get a compile error. Will store 3.000000000 Will store 3 Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

Problem: Keeping Two Digits After Decimal Points Write a program that displays the sales tax with two digits after the decimal point. publicclass SalesTax { publicstaticvoid main(String[] args) { double purchaseAmount = 197.55; double tax = purchaseAmount * 0.06; System.out.println("Sales tax is $" + tax); System.out.println("Sales tax is $" + (int)(tax * 100) / 100.0); } } Sales tax is $11.853 Sales tax is $11.85 Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

Character Data Type Four hexadecimal digits. char letter = 'A'; (ASCII) char numChar = '4'; (ASCII) char letter = '\u0041'; (Unicode) char numChar = '\u0034'; (Unicode) NOTE: The increment and decrement operators can also be used on char variables to get the next or preceding Unicode character. For example, the following statements display character b. char ch = 'a'; System.out.println(++ch); Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

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

Problem: Displaying Unicodes Write a program that displays two Chinese characters and three Greek letters. import javax.swing.JOptionPane; public class DisplayUnicode { public static void main(String[] args) { JOptionPane.showMessageDialog(null, "\u6B22\u8FCE \u03b1 \u03b2 \u03b3", "\u6B22\u8FCE Welcome", JOptionPane.INFORMATION_MESSAGE); } } Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

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

1 2 Appendix B: ASCII Character Set ASCII Character Set is a subset of the Unicode from \u0000 to \u007f Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

1 2 ASCII Character Set, cont. ASCII Character Set is a subset of the Unicode from \u0000 to \u007f Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

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

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

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 Create a String type named message and store “Welcome to Java” at that location Create a String type named s and store “Chapter2” at that location Create a String type named s1 and store “SupplementB” at that location Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

String Concatenation (cont.) // add to message String message = "Welcome " + "to " + "Java"; Message = message + “! Good luck!!” Create a String type named message and store “Welcome to Java” at that location. Then add “! Good luck!!” to message and now “Welcome to Jave! Good luck!!” is stored at location message. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

Obtaining Input This book provides two ways of obtaining input. • Using JOptionPane input dialogs (§2.11) • Inputs from a GUI window. • Using the JDK 1.5 Scanner class (§2.16) • Inputs from DOS window or lower pane in Eclipse workspace. Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

Chapter 2 Elementary Programming