Random number

1. Random number • Random numbers • are often needed when writing software • Flight simulator use random numbers • to determine how often simulated flights has engine trouble • are generated in JAVA through the Randomclass • Part of the java.util package • Picks a number at random out of a range of values

2. Random class • Methods of Random class • float nextFloat() • returns a random number • between 0.0 (inclusive) and 1.0 (exclusive) • int nextInt() • Returns a random number over all possible int value • int nextInt(int num) • Returns a random number in the range 0 to num-1 • Refer to RandomNumbers.java

3. Math class • Mathclass • provides a large number of basic mathematical functions • Helpful in making calculations • is defined in java.langpackage • includes static methods • => methods can be invoked through the name of the class • They can be used without having to instantiate an object • Return values used in expressions as needed value = Math.cos(90) + Math.sqrt(delta);

4. Using Math class • Sample program • Use Math class • to compute the roots of a quadratic equation • ax2 + bx +c • Algorithm • Read values (a, b, and c) • Evaluate the roots of the equation • Refer to Quadratic.java

5. Some methods of the Math class • static int abs(int num) • The absolute value of num • static double cos(double angle) • Returns the angle (in radians) cosine • static double exp(double power) • Returns the value of e raised to the specified power

6. Using Math class • Sample program • Use Math class • to compute the roots of a quadratic equation • ax2 + bx +c • Algorithm • Read values (a, b, and c) • Evaluate the roots of the equation • Refer to Quadratic.java

7. Some methods of the Math class • static int abs(int num) • The absolute value of num • static double cos(double angle) • Returns the angle (in radians) cosine • static double exp(double power) • Returns the value of e raised to the specified power

8. Outline Creating Objects The String Class Packages Formatting Output Enumerated Types Wrapper Classes Components and Containers Images

9. Formatting output • It is often necessary to format values • output looks appropriate when printed or displayed • NumberFormat part of java.text package • Provides generic formatting capabilities • is not instantiated using the new operator • instead by requesting an object • From one of the static methods invoked thru the class name • NumberFormat fmt = NumberFormat.getCurrencyInstance();

10. Creating NumberFormat instance • NumberFormat objects • are created using • getCurrencyInstance() invoked thru class name • returns a formatter for monetary values • getPercentInstance() invoked thru class name • returns an object that formats a percentage • are used to format numbers using method format() • Refer to Purchase.java NumberFormat fmt = NumberFormat.getCurrencyInstance() double subtotal=19.35; System.out.println(fmt.format(subtotal) ); Output: $19.35

11. DecimalFormat class • DecimalFormat part of java.text package • allows to format values based on a pattern • To determine how many digits should be printed • To the right of the decimal point (for instance) • is instantiated in the traditional way • using the new operator • Its constructor DecimalFormat takes a String • That represents a pattern for the formatted number • Refer to CircleStats.java

12. Outline Creating Objects The String Class Packages Formatting Output Enumerated Types Wrapper Classes Components and Containers Images

13. Enumerated types • Java allows you to define an enumerated type • Which can then be used to declare variables • as the type of a variable • establishes all possible values for a variable of that type • By listing, or enumerating the values • Where the values are identifiers, and can be anything desired • enum Season {winter, spring, summer, fall} • There is no limit to the number of listed values • Any number of values can be listed

14. Declaring and using an enumerated type • Once a type is defined • A variable of that type can be declared • enum Grade {A, B, C, D, F}; Grade score; • And it can be assigned a value • Thru the name of the type score = Grade.A; • Enumerated types are type-safe • You cannot assign any value other than those listed

15. Ordinal values • Internally, each value of an enumerated type • is stored as an integer, called its ordinal value • The first value has an ordinal value of zero • The second one, and so on • You cannot assign a numeric value • to enumerated type, even if it corresponds to an ordinal value

16. Enumerated types: methods • The declaration of an enumerated type • is a special type of class • And each variable of that type is an object • methods associated with enumerated objects • The ordinal() method returns the numeric value • Of an enumerated type • The name() returns the name of the value • Refer to IceCream.java

17. Outline Creating Objects The String Class Packages Formatting Output Enumerated Types Wrapper Classes Components and Containers Images

18. Wrapper classes • A wrapper class • is used to wrap a primitive value into an object • Ex: create an object that serves as a container to hold an int • represents a particular primitive type • Ex: Integer class represents a simple integer value • instantiated, stores a single primitive type value • Ex: Integerobject store a single int value • its constructor accept the primitive value to store • Ex: Integer ageObj = new Integer (40);

19. Wrapper classes in the JAVA class library • For each primitive type in JAVA • There exists a corresponding wrapper class (java.lang)

20. Wrapper classes methods • Wrapper classes methods • manages the associated primitive type • Ex: Integerprovides methods returning the int stored in it • Some methods of the Integer class • Integer (int value) • Constructor: creates an new Integer object storing value • float floatValue() • returns the value of this integer as the float type • static int parseInt (String str) • Returns the int corresponding to the value in str

21. Autoboxing/Unboxing • Autoboxing is the automatic conversion between • Primitive value and corresponding wrapper object • Integer obj1; int num1 = 69; Obj1 = num1; // automatically creates an Integer object • Unboxing is the reverse condition • Integer obj2 = new Integer (69); int num2; num2 = Obj2; // automatically extracts the int value • Refer to wrapper_error.java

22. Using Dialog Boxes for Input/Output • Another way to gather input is to use a GUI • such as JOptionPane offered by Java • Which allows a programmer to use GUI for I/O • Making I/O more efficient and the program more attractive • JOptionPane • Contained in the package javax.swing • Offers two methods: • ShowInputDialog: allows user to input a string from keyboard • ShowMessageDialog: allows user to display results

23. Syntax for ShowInputDialog • To display a dialog box • Containing the string in the object stringExpression • Storing the input data in the String object str • The syntax to use the method is: • str = JOptionPane.showInputDialog(stringExpression); • A dialog appears on the screen • prompting user to enter data • Data is returned as a string and assigned to variable str • The user enters the data in the white area • Called text field

24. Syntax for showMessageDialog • The syntax to use showMessageDialog is • JoptionPane.showMessageDialog(null, messageStringExpression, boxTitleString, messageType). • messageStringExpression:evaluated and value appears in box • boxTitleString: the title of the dialog box • messageType: type of icon appearing in the dialog box • JoptionPane.ERROR_MESSAGE • JoptionPane.INFORMATION_MESSAGE • JoptionPane.Question_MESSAGE • JoptionPane.PLAIN_MESSAGE • JoptionPane.WARNING_MESSAGE