1 Scanner, Documentation, Style Keyboard Input  Java 5.0 has reasonable facilities for handling keyboard input.  These facilities are provided by the Scanner class in the java.util package.  A package is a library of classes. Using the Scanner Class  Near the beginning of your program, insert import java.util.Scanner;  Create an object of the Scanner class Scanner keyboard = new Scanner (System.in)  Read data (an int or a double, for example) int n1 = keyboard.nextInt(); double d1 = keyboard,nextDouble(); Some Scanner Class Methods  Figure 2.7a2 Some Scanner Class Methods nextLine()Method Caution  The nextLine() method reads  The remainder of the current line,  Even if it is empty. nextLine()Method Caution  Example – given following declaration. int n; String s1, s2; n = keyboard.nextInt(); s1 = keyboard.nextLine(); s2 = keyboard.nextLine();  Assume input shown n is set to 42 but s1 is set to the empty string. 42 and don't you forget it. The Empty String  A string can have any number of characters, including zero.  The string with zero characters is called the empty string.  The empty string is useful and can be created in many ways including String s3 = "";3 Other Input Delimiters (optional)  Almost any combination of characters and strings can be used to separate keyboard input.  to change the delimiter to "##" keyboard2.useDelimiter("##");  whitespace will no longer be a delimiter for keyboard2 input Documentation and Style: Outline  Meaningful Names  Comments  Indentation  Named Constants Documentation and Style  Most programs are modified over time to respond to new requirements.  Programs which are easy to read and understand are easy to modify.  Even if it will be used only once, you have to read it in order to debug it . Meaningful Variable Names  A variable's name should suggest its use.  Observe conventions in choosing names for variables.  Use only letters and digits.  "Punctuate" using uppercase letters at word boundaries (e.g. taxRate).  Start variables with lowercase letters.  Start class names with uppercase letters.4 Comments  The best programs are self-documenting.  Clean style  Well-chosen names  Comments are written into a program as needed explain the program.  They are useful to the programmer, but they are ignored by the compiler. Comments  A comment can begin with //.  Everything after these symbols and to the end of the line is treated as a comment and is ignored by the compiler. double radius; //in centimeters Comments  A comment can begin with /* and end with */  Everything between these symbols is treated as a comment and is ignored by the compiler. /** This program should only be used on alternate Thursdays, except during leap years, when it should only be used on alternate Tuesdays. */ Comments  A javadoc comment, begins with /** and ends with */.  It can be extracted automatically from Java software. /** method change requires the number of coins to be nonnegative */5 When to Use Comments  Begin each program file with an explanatory comment  What the program does  The name of the author  Contact information for the author  Date of the last modification.  Provide only those comments which the expected reader of the program file will need in order to understand it. Comments Example  See Comments.sample.txt Indentation  Indentation should communicate nesting clearly.  A good choice is four spaces for each level of indentation.  Indentation should be consistent.  Indentation should be used for second and subsequent lines of statements which do not fit on a single line. Indentation  Indentation does not change the behavior of the program.  Proper indentation helps communicate to the human reader the nested structures of the program6 Using Named Constants  To avoid confusion, always name constants (and variables). area = PI * radius * radius; is clearer than area = 3.14159 * radius * radius;  Place constants near the beginning of the program. Named Constants  Once the value of a constant is set (or changed by an editor), it can be used (or reflected) throughout the program. public static final double INTEREST_RATE = 6.65;  If a literal (such as 6.65) is used instead, every occurrence must be changed, with the risk than another literal with the same value might be changed unintentionally. Declaring Constants  Syntax public static final Variable_Type = Constant;  Examples public static final double PI = 3.14159; public static final String MOTTO = "The customer is always right.";  By convention, uppercase letters are used for constants. Named Constants  see CircleCalculation2 Sample Screen