Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Chapter 2 Elementary Programming

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved 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. Java comes with 8 primitive data types that split into four categories to handle simple data values: Integers, floating points, characters, truth values; Integers hold number values that cannot have a fractional part. There are four different types: byte, short, int, & long

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Objectives F To write Java programs to perform simple calculations (§2.2). F To obtain input from the console using the Scanner class (§2.3). F To use identifiers to name variables, constants, methods, and classes (§2.4). F To use variables to store data (§§ ). F To program with assignment statements and assignment expressions (§2.6). F To use constants to store permanent data (§2.7). F To declare Java primitive data types: byte, short, int, long, float, double, and char (§§2.8.1). F To use Java operators to write numeric expressions (§§2.8.2–2.8.3). F To display current time (§2.9). F To use short hand operators (§2.10). F To cast value of one type to another type (§2.11). F To compute loan payment (§2.12). F To represent characters using the char type (§2.13). F To compute monetary changes (§2.14). F To represent a string using the String type (§2.15). F To become familiar with Java documentation, programming style, and naming conventions (§2.16). F To distinguish syntax errors, runtime errors, and logic errors and debug errors (§2.17). F (GUI) To obtain input using the JOptionPane input dialog boxes (§2.18).

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Listing Computing Average 1 import java.util.Scanner; // Scanner is in the java.util package 3 public class ComputeAverage { 4 public static void main(String[] args) { 5 // Create a Scanner object 6 Scanner input = new Scanner(System.in); 7 8 // Prompt the user to enter three numbers 9 System.out.print("Enter three numbers: "); 10 double number1 = input.nextDouble(); 11 double number2 = input.nextDouble(); 12 double number3 = input.nextDouble(); // Compute average 15 double average = (number1 + number2 + number3) / 3; // Display result 18 System.out.println("The average of " + number1 + " " + 19 number2 + " " + number3 + " is " + average); 20 } 21 } 4

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Introducing Programming with an Example Listing 2.1 Computing the Area of a Circle - This program computes the area of the circle. ComputeArea Run public class ComputeArea { public static void main(String[] args) { double radius; // Declare radius double area; // Declare area // Assign a radius radius = 20; // New value is radius // Compute area // Statement assigned to area and line end with ; area = radius * radius * ; // Display results using print statement System.out.println("The area for the circle of radius " + radius + " is " + area); } }

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved 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 * ; // Display results System.out.println("The area for the circle of radius " + radius + " is " + area); } no value radius allocate memory for radius animation Note: the plus sign (+) in the program allows string to link or continues into a larger strings, which it can display in the output.

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved 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 * ; // 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

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved 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 * ; // Display results System.out.println("The area for the circle of radius " + radius + " is " + area); } 20 radius no value area assign 20 to radius animation

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved 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 * ; // Display results System.out.println("The area for the circle of radius " + radius + " is " + area); } 20 radius memory area compute area and assign it to variable area animation

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved 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 * ; // Display results System.out.println("The area for the circle of radius " + radius + " is " + area); } 20 radius memory area print a message to the console animation

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Reading Input from the Console 1. Create a Scanner object (Scanner Class is a class in java.util, which allows the user to read values/data(e.g.numbers) of various types, which can be resolve from primitive (original) types and strings.) Table Scanner input = new Scanner(System.in); 2. Use the methods next(), nextByte(), nextShort(), nextInt(), nextLong(), next Float(), 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 input = new Scanner(System.in); double d = input.nextDouble(); ComputeAreaWithConsoleInputComputeAverage

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Class, Object and Methods in Java F Class: Whatever we can see in this world all the things are a object. F And all the objects are categorized in a special group. That group is termed as a class (blueprint to create instances of itself). F Almost all the properties of the object should be matched with it's own class. F Methods enable a class object's behavior example: car (class), shape, size, color (attributes), car convertible (Object), the convertible is open and closes is the behavior of the class (methods). 12

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved 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.

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Variables Variables are used to store values to be used later in a program. // Compute the first area radius = 1.0; area = radius * radius * ; System.out.println("The area is “ + area + " for radius "+radius); // Compute the second area radius = 2.0; area = radius * radius * ; System.out.println("The area is “ + area + " for radius "+radius);

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved 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;

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Assignment Statements After variable declared, Assignment statement can be used (=); The syntax is: variable = expressions; x = 1; // Assign 1 to x; radius = 1.0; // Assign 1.0 to radius; a = 'A'; // Assign 'A' to a;

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Constants Value of the variable may not be change during the execution for a program. /* A constant must be declared and initialized in the same statement. */ /* The word final is a Java keyword fro declaring a constant. */ //A Constants are named in uppercase final datatype CONSTANTNAME = VALUE; final double PI = ; final int SIZE = 3;

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Numerical Data Types Primitive Data types Primitive Data types (The Java Tutorials Link)

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Numeric Operators

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Integer Division +, -, *, /, and % 5 / 2 yields an integer 2. (when both operands of a division are integers, the result of the division is an integer and the fraction will be truncated). 5.0 / 2 yields a double value 2.5 (when operands of a division are floating-point number, the result of the division is an integer). 5 % 2 yields 1 (the remainder of the division), 5 percent of 2 is 1

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Remainder Operator Remainder is very useful in programming. For example, an even number % 2 is always 0 and 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, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Problem: Displaying Time Write a program that obtains hours and minutes from seconds. DisplayTime Run import java.util.Scanner; public class DisplayTime { public static void main(String[] args) { Scanner input = new Scanner(System.in); // Prompt the user for input System.out.print("Enter an integer for seconds: "); int seconds = input.nextInt(); int minutes = seconds / 60; // Find minutes in seconds int remainingSeconds = seconds % 60; // Seconds remaining System.out.println(seconds + " seconds is " + minutes + " minutes and " + remainingSeconds + " seconds"); } }

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved NOTE Calculations involving floating-point numbers are approximated because these numbers are not stored with complete accuracy. For example, System.out.println( ); displays , not 0.5, and System.out.println( ); displays , not 0.1. Integers are stored precisely. Therefore, calculations with integers yield a precise integer result.

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved 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 = ; double d = 5.0;

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved 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 ( ) to 2 31 –1 ( ). 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, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved 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.

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Scientific Notation Floating-point literals can also be specified in scientific notation, for example, e+2, same as e2, is equivalent to , and e-2 is equivalent to E (or e) represents an exponent and it can be either in lowercase or uppercase e2, is equivalent to x 10²=

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved 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, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved 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.

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Problem: Converting Temperatures Write a program that converts a Fahrenheit degree to Celsius using the formula: FahrenheitToCelsius Run Exercise Listing 2.5: Type the program from the textbook

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Problem: Displaying Current Time Write a program that displays current time in GMT in the format hour:minute:second such as 1:45:19. The currentTimeMillis method in the System class returns the current time in milliseconds since the midnight, January 1, 1970 GMT. (1970 was the year when the Unix operating system was formally introduced.) You can use this method to obtain the current time, and then compute the current second, minute, and hour as follows. ShowCurrentTime Run

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Shortcut Assignment Operators OperatorExampleEquivalent +=i += 8i = i + 8 -=f -= 8.0f = f *=i *= 8i = i * 8 /=i /= 8i = i / 8 %=i %= 8i = i % 8 Very often the value of a variable is used, modified, and then re- assigned back to the same variable. See below example and equivalent. The += called the addition assignment operator.

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Increment & Decrement Operators OperatorNameDescription ++var preincrementThe 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. --var predecrementThe 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. The ++ ad -- operators can be used in prefix or suffix, as shown below Example: int i = 3, j = 3; i++; // i becomes 4 j--; // j becomes 2

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Assignment Statements Prior to Java 2, all the expressions can be used as statements. Since Java 2, only the following types of expressions can be statements: variable op= expression; // Where op is +, -, *, /, or % ++variable; increment var by 1 and use the new var value variable++; increment var by 1 and use the original var value --variable; decrement var by 1 and use the new var value variable--; decrement var by 1 and use the original var value

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Increment and Decrement Operators, cont. i ++ means Increment after 10 * 10 (original value of i ) is 100 i is increment by 1 before, and the new value of i is returned and used in the multiplication, Thus newNum becomes 110. i is increment by 1 after, and the old value of i is returned and used in the multiplication, Thus newNum becomes 100.

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Numeric Type Conversion Binary operations with two operands: if an integer and a floating number are involved in a binary operation, Java automatically converts the integer to a floating-point value. Example: 3 * 4.5 is the same as 3.0 * 4.5. Consider the following statements: byte i = 100; long k = i * 3 + 4; double d = i * k / 2;

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Conversion Rules When performing a binary operation involving two operands of different types, Java automatically converts the operand based on the following rules: So, 3*4.5 is the same as 3.0* 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, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Type Casting A character (char) can be cast into any numeric type and vice versa. When an integer is cast into a char, only is lower 16 bits of data are used, the other part is ignored. 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;

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Problem: Keeping Two Digits After Decimal Points Write a program that displays the sales tax with two digits after the decimal point. SalesTax Run import java.util.Scanner; public class SalesTax { public static void main(String[] args) { Scanner input = new Scanner(System.in); System.out.print("Enter purchase amount: "); double purchaseAmount = input.nextDouble(); double tax = purchaseAmount * 0.06; System.out.println("Sales tax is " + (int)(tax * 100) / 100.0); } }

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Problem: Computing Loan Payments ComputeLoanRun This program lets the user enter the interest rate, number of years, and loan amount and computes monthly payment and total payment.

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Character Data Type char letter = 'A'; (ASCII) char numChar = '4'; (ASCII) char letter = '\u0041'; (Unicode) char numChar = '\u0034'; (Unicode) Four hexadecimal digits. 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, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Unicode & ASCII code F Computers use binary numbers internally as character is stored in a computer as a sequence of 0’s & 1’s. F Mapping the character to its binary called encoding. F Java supports Unicode, as encoding scheme characters established. 42

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved 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 characters. Unicode \u03b1 \u03b2 \u03b3 for three Greek letters

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Problem: Displaying Unicodes Write a program that displays two Chinese characters and three Greek letters. DisplayUnicode Run

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved 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, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Appendix B: ASCII Character Set ASCII Character Set is a subset of the Unicode from \u0000 to \u007f

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved ASCII Character Set, cont. ASCII Character Set is a subset of the Unicode from \u0000 to \u007f

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved 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, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Problem: Monetary Units This program lets the user enter the amount in decimal representing dollars and cents and output a report listing the monetary (pertaining to money) equivalent in single dollars, quarters, dimes, nickels, and pennies. Your program should report maximum number of dollars, then the maximum number of quarters, and so on, in this order. ComputeChangeRun

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Trace ComputeChange int remainingAmount = (int)(amount * 100); // Find the number of one dollars int numberOfOneDollars = remainingAmount / 100; remainingAmount = remainingAmount % 100; // Find the number of quarters in the remaining amount int numberOfQuarters = remainingAmount / 25; remainingAmount = remainingAmount % 25; // Find the number of dimes in the remaining amount int numberOfDimes = remainingAmount / 10; remainingAmount = remainingAmount % 10; // Find the number of nickels in the remaining amount int numberOfNickels = remainingAmount / 5; remainingAmount = remainingAmount % 5; // Find the number of pennies in the remaining amount int numberOfPennies = remainingAmount; 1156 remainingAmount remainingAmount initialized Suppose amount is 11.56

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Trace ComputeChange int remainingAmount = (int)(amount * 100); // Find the number of one dollars int numberOfOneDollars = remainingAmount / 100; remainingAmount = remainingAmount % 100; // Find the number of quarters in the remaining amount int numberOfQuarters = remainingAmount / 25; remainingAmount = remainingAmount % 25; // Find the number of dimes in the remaining amount int numberOfDimes = remainingAmount / 10; remainingAmount = remainingAmount % 10; // Find the number of nickels in the remaining amount int numberOfNickels = remainingAmount / 5; remainingAmount = remainingAmount % 5; // Find the number of pennies in the remaining amount int numberOfPennies = remainingAmount; 1156 remainingAmount Suppose amount is numberOfOneDollars numberOfOneDollars assigned animation

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Trace ComputeChange int remainingAmount = (int)(amount * 100); // Find the number of one dollars int numberOfOneDollars = remainingAmount / 100; remainingAmount = remainingAmount % 100; // Find the number of quarters in the remaining amount int numberOfQuarters = remainingAmount / 25; remainingAmount = remainingAmount % 25; // Find the number of dimes in the remaining amount int numberOfDimes = remainingAmount / 10; remainingAmount = remainingAmount % 10; // Find the number of nickels in the remaining amount int numberOfNickels = remainingAmount / 5; remainingAmount = remainingAmount % 5; // Find the number of pennies in the remaining amount int numberOfPennies = remainingAmount; 56 remainingAmount Suppose amount is numberOfOneDollars remainingAmount updated animation

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Trace ComputeChange int remainingAmount = (int)(amount * 100); // Find the number of one dollars int numberOfOneDollars = remainingAmount / 100; remainingAmount = remainingAmount % 100; // Find the number of quarters in the remaining amount int numberOfQuarters = remainingAmount / 25; remainingAmount = remainingAmount % 25; // Find the number of dimes in the remaining amount int numberOfDimes = remainingAmount / 10; remainingAmount = remainingAmount % 10; // Find the number of nickels in the remaining amount int numberOfNickels = remainingAmount / 5; remainingAmount = remainingAmount % 5; // Find the number of pennies in the remaining amount int numberOfPennies = remainingAmount; 56 remainingAmount Suppose amount is numberOfOneDollars 2 numberOfOneQuarters numberOfOneQuarters assigned animation

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Trace ComputeChange int remainingAmount = (int)(amount * 100); // Find the number of one dollars int numberOfOneDollars = remainingAmount / 100; remainingAmount = remainingAmount % 100; // Find the number of quarters in the remaining amount int numberOfQuarters = remainingAmount / 25; remainingAmount = remainingAmount % 25; // Find the number of dimes in the remaining amount int numberOfDimes = remainingAmount / 10; remainingAmount = remainingAmount % 10; // Find the number of nickels in the remaining amount int numberOfNickels = remainingAmount / 5; remainingAmount = remainingAmount % 5; // Find the number of pennies in the remaining amount int numberOfPennies = remainingAmount; 6 remainingAmount Suppose amount is numberOfOneDollars 2 numberOfQuarters remainingAmount updated animation

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved 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 & Scanner. The String type is not a primitive type, more like 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 (link two or more information) strings.

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved String Concatenation Two string can be concatenated (link together) with sign (+) operator. If one of the operands is a nonstring (e.g., a number), the nonstring value is converted into a string and link with other string. Here are some examples: // Strings are concatenated String message = "Welcome " + "to " + "Java"; The shorthand += operator can also be used for string concatenate. for example the following appends the string message += “and Java is fun”; So, the new message is “Welcome to Java and Java is fun”.

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved String Concatenation Cont.. System.out.println("The average of " + number1 + " " + number2 + " " + number3 + " is " + average); // 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'; // s1 becomes SupplementB 57

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Programming Style and Documentation F Appropriate Comments //comments F Naming Conventions F Proper Indentation and Spacing Lines F Block Styles

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved 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 the following: your name, class section, instructor, program date and a brief description at the beginning of the program.

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved 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.

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved 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

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Proper Indentation and Spacing  Indentation –Indent two spaces. F Spacing –Use blank line to separate segments of the code.

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Block Styles Use end-of-line style for braces.

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Programming Errors F Programming errors are unavoidable even for expert programmers. Errors can be categorized into three types. F Syntax Errors –Detected by the compiler F Runtime Errors –Causes the program to abort F Logic Errors –Produces incorrect result

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Syntax Errors public class ShowSyntaxErrors { public static void main(String[] args) { i = 30; System.out.println(i + 4); } Errors that occur during the compilation, during coding construction such as mistyping a keyword, omitted some necessary punctuation or opening brace without closing brace are called syntax error or compiler errors. Syntax error are usually easy to detect, because the compiler tells you where they are and what caused them.

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Runtime Errors public class ShowRuntimeErrors { public static void main(String[] args) { int i = 1 / 0; } Runtime error cause a program to terminate abnormally. They occur while a program is running if then environment detects an operation is impossible to carry out. Example is:  input incorrect type of value ( double value instead of integer value)  division by 0

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Logic Errors // ShowLogicErrors.java: the program contains a logic error public class ShowLogicErrors { public static void main (String [] args) { // Add number1 to number2 int number1 = 3; int number2 = 3; number2 += number1 + number2; System.out.println ("number2 is " + number2); } } Logic error occur when a program does not perform the way it was intended to. Error of this kind occur for many different reasons. Example below is add to number1 to number2 Note: The program above have no syntax, runtime errors, but it doe not print the correct result for number2. See if you can find the error.

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved 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.

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved 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.

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved JOptionPane Input This book provides two ways of obtaining input. 1. Using the Scanner class (console input) 2. Using JOptionPane input dialogs (obtain from an input dialog box by invoke the JOptionPane.showInputDialog methods JOptionPane makes it easy to pop up a standard dialog box that prompts users for a value or informs them of something. Class JOptionPane

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Getting Input from Input Dialog Boxes String input = JOptionPane.showInputDialog( "Enter an input");

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Getting Input from Input Dialog Boxes String string = JOptionPane.showInputDialog( null, “Prompting Message”, “Dialog Title”, JOptionPane.QUESTION_MESSAGE);

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Two Ways to Invoke the Method There are several ways to use the showInputDialog method. For the time being, you only need to know two ways to invoke it. One is to use a statement as shown in the example: String string = JOptionPane.showInputDialog(null, x, y, JOptionPane.QUESTION_MESSAGE); where x is a string for the prompting message, and y is a string for the title of the input dialog box. The other is to use a statement like this: JOptionPane.showInputDialog(x); where x is a string for the prompting message.

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved 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”.

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved 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”.

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved Problem: Computing Loan Payments Using Input Dialogs ComputeLoanUsingInputDialog Run Same as the preceding program for computing loan payments, except that the input is entered from the input dialogs and the output is displayed in an output dialog.