CiS 260: App Dev I

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Introduction to Methods A method (or ________) is a segment of code

that performs a specific task. Advantages of modular program design:

allows you to focus on a small part of the programmany programmers can work on different methodsencourages software reuse improves the simplicity and readability of programs

Java provides ___________ methods in collections of classes called class __________.

Examples of predefined methods are println(), showInputDialog(), setText(), etc.

The programmer can create his own ___________ methods in classes he creates.

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Predefined Methods An algebraic function looks like f( x ) = 2x + 5

f is the name of the function2x + 5 is the body of the functionx is the parameter of the function, any real number if x = 2, we write f( 2 ) and 2 is the argument of f f(2) = 2 * 2 + 5 = ___.

Java has a pow(x, y) method in the Math classpow is the name of the methodx and y are the ____________ of the method, both

of type doubleFor the arguments x=2 and y=3, Math.pow(2, 3)

means 2 raised to the power 3, or ___ You often need to use the import statement.

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User-Defined Methods Predefined methods are prewritten to perform

common, basic tasks. User-defined methods are ________ designed

to perform very specialized tasks. Two kinds of user-defined methods

value-returning (returns a result to the calling method)

void (doesn’t return a result, just executes)

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Value-Returning Method Every method has these five parts

name (such as pow or myCustomMethod)parameter list (in parentheses)______ type of each parameter, like double the data type of the returned value, like double the program code executed by the method

The first four above constitute the method __________ and the last is called the ______.

The five components above constitute a method definition.

To use a method in a program, you must code a method _______.

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Method Example Suppose you wrote the following methodpublic static double raiseToAPower (double base,

double exponent)

{

double result = 1;

for( int i = 1; i <= exponent; i++ )

result *= base;

return result;

}

public and static are modifiers, double is the return type, and raiseToAPower is the ______.

(double base, double exponent) is the parameter list and the code inside the {}’s is the ______.

Class With a User-Defined Methodpublic class Power{

public static void main( String[] args ){

double answer;answer = raiseToAPower( 2,3 ); // method ______System.out.println(answer); // displays 8.0

} // end main

public static double raiseToAPower (double base, double exponent){

double result = 1;for( int i = 1; i <= exponent; i++ )

result *= base;return result; // return this value to main

} // end raiseToAPower} // end class

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The Return Statement The syntax of a return statement in a method is return

expr; where expr is a variable, constant value, or ____________.

The data type of the value of expr must match the _______ type of the method.

When a return statement executes, the method terminates and control goes back to the ________.

public static double larger( double x, double y ){

double max;if( x >= y )

max = x;else

max = y;return max;

}

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Flow of Execution The order of methods in a class doesn’t matter. When a program executes, the first statement in

the method ________ executes first. When the last statement of a method executes,

control is passed back to the point immediately following the method call.

For a value-returning method, the value that the method returns replaces the method call and execution follows immediately after the call.

A _________statement can be used in a void method to exit a method early.

To call a void method, use methodName();

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Data Types and Parameters

For primitive data types, variables are passed from one method to another by ______ .

This means methods have their own copies of primitive data separate from each other.

For reference variables (objects or abstract data types) variables are passed by __________.

Therefore, a change in the value for a reference variable in one method, automatically changes it in any other method.

Remember that a variable of type String is a reference variable (points to a String _______).

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Scope of an Identifier The scope of an identifier is that part of the

program in which it is accessible (________). A ______ identifier is declared within a method

or block and is visible only within that method or block.

When a counter variable is declared in a for loop, its scope is limited to the for loop.

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Method Overloading In Java, a class can contain several methods

with the same name. However, methods with the same name must

have different _________________. This is called method ____________. This makes the naming of methods easier.

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The class String In Java, a string is not a variable, but an _____. The following two statements are equivalent:

String name = “Lisa Johnson”;name = new String( “Lisa Johnson” );

name is actually a reference variable that contains the address of the String ________.

A string contains ___ or more characters enclosed in double quotes.

The ________ of the first character in a string is 0, of the second character is 1, and so on.

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Methods in the class String The method substring() is a member of class String.

Using String name = “Lisa Johnson”; :name.substring(0,4) yields _______name.substring(5,12) yields “Johnson”name.indexOf(‘J’) yields ___name.charAt(4) yields ‘ ’name.equals(“Lisa Johnson”) yields truename.equals(“Luke Johnson”) yields ______name.length() yields ____name.replace('i','e') yields “Lesa Johnson”

The String object name has access to the String methods using the ____ operator.

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Formatting Numbers You can format numbers in your program using

complicated program logic (see p. 226) Or you can use Java pre-defined methods:

NumberFormat decimal = NumberFormat.getNumberInstance();

decimal.setMaximumFractionDigits(2); String aDecimalStr = decimal.format(19.857); //19.86

NumberFormat percent = NumberFormat.getPercentInstance();

String aPercentStr = percent.format(.857); // 86%

NumberFormat currency =

NumberFormat.getCurrencyInstance(); String aCurrencStr = currency.format(19.95); //$19.95

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The Calendar Class Calendar today = Calendar.getInstance();

int month = today.get( Calendar.MONTH ) + 1; // returns numeric month (1 for Jan, 2 for Feb, …)

Date todaysDate = today.getTime(); System.out.print( todaysDate ); // prints date & time

Calendar dueDate = Calendar.getInstance();

dueDate.set( 2007, 11, 31 ); // due date is Dec. 31

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The GregorianCalendar Class

GregorianCalendar birthDate = new GregorianCalendar( 1953, 8, 10 ); // Sept. 10, 1953

int dayOfWeek = birthDate.get( GregorianCalendar.DAY_OF_WEEK ); // returns, for example, Tuesday

Long birthTime = birthDate.getTimeInMillis();

// time in milliseconds DateFormat longDate = DateFormat.getDateInstance( DateFormat.LONG );

String birthDayStr = longDate.format( birthDate ); // “September 10, 1953”