Notes on Declaring and Using Methods

There are three ways to call a method:

  1. Using a method name by itself to call another method of the same classsuch as maximum( number1, number2, number3 ) in line 21 of Fig. 6.3.
  2. Using a variable that contains a reference to an object, followed by a dot (.) and the method name to call a method of the referenced objectsuch as the method call in line 10 of Fig. 6.4, maximumFinder.determineMaximum(), which calls a method of class MaximumFinder from the main method of MaximumFinderTest.
  3. Using the class name and a dot (.) to call a static method of a classsuch as Math.sqrt( 900.0 ) in Section 6.3.

Note that a static method can call only other static methods of the same class directly (i.e., using the method name by itself) and can manipulate only static fields in the same class directly. To access the class's non-static members, a static method must use a reference to an object of the class. Recall that static methods relate to a class as a whole, whereas non-static methods are associated with a specific instance (object) of the class and may manipulate the instance variables of that object. Many objects of a class, each with its own copies of the instance variables, may exist at the same time. Suppose a static method were to invoke a non-static method directly. How would the method know which object's instance variables to manipulate? What would happen if no objects of the class existed at the time the non-static method was invoked? Clearly, such a situation would be problematic. Thus, Java does not allow a static method to access non-static members of the same class directly.

There are three ways to return control to the statement that calls a method. If the method does not return a result, control returns when the program flow reaches the method-ending right brace or when the statement


is executed. If the method returns a result, the statement

      return expression;

evaluates the expression, then returns the result to the caller.

Common Programming Error 6.4

Declaring a method outside the body of a class declaration or inside the body of another method is a syntax error.

Common Programming Error 6.5

Omitting the return-value-type in a method declaration is a syntax error.

Common Programming Error 6.6

Placing a semicolon after the right parenthesis enclosing the parameter list of a method declaration is a syntax error.

Common Programming Error 6.7

Redeclaring a method parameter as a local variable in the method's body is a compilation error.

Common Programming Error 6.8

Forgetting to return a value from a method that should return a value is a compilation error. If a return value type other than void is specified, the method must contain a return statement that returns a value consistent with the method's return-value-type. Returning a value from a method whose return type has been declared void is a compilation error.

Introduction to Computers, the Internet and the World Wide Web

Introduction to Java Applications

Introduction to Classes and Objects

Control Statements: Part I

Control Statements: Part 2

Methods: A Deeper Look


Classes and Objects: A Deeper Look

Object-Oriented Programming: Inheritance

Object-Oriented Programming: Polymorphism

GUI Components: Part 1

Graphics and Java 2D™

Exception Handling

Files and Streams


Searching and Sorting

Data Structures



Introduction to Java Applets

Multimedia: Applets and Applications

GUI Components: Part 2



Accessing Databases with JDBC


JavaServer Pages (JSP)

Formatted Output

Strings, Characters and Regular Expressions

Appendix A. Operator Precedence Chart

Appendix B. ASCII Character Set

Appendix C. Keywords and Reserved Words

Appendix D. Primitive Types

Appendix E. (On CD) Number Systems

Appendix F. (On CD) Unicode®

Appendix G. Using the Java API Documentation

Appendix H. (On CD) Creating Documentation with javadoc

Appendix I. (On CD) Bit Manipulation

Appendix J. (On CD) ATM Case Study Code

Appendix K. (On CD) Labeled break and continue Statements

Appendix L. (On CD) UML 2: Additional Diagram Types

Appendix M. (On CD) Design Patterns

Appendix N. Using the Debugger

Inside Back Cover

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Java(c) How to Program
Java How to Program (6th Edition) (How to Program (Deitel))
ISBN: 0131483986
EAN: 2147483647
Year: 2003
Pages: 615
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