Memory Concepts

Variable names such as number1, number2 and sum actually correspond to locations in the computer's memory. Every variable has a name, a type, a size and a value.

In the addition program of Fig. 2.7, when the statement (line 18)

 number1 = input.nextInt(); // read first number from user

executes, the number typed by the user is placed into a memory location to which the name number1 has been assigned by the compiler. Suppose that the user enters 45. The computer places that integer value into location number1, as shown in Fig. 2.8. Whenever a value is placed in a memory location, the value replaces the previous value in that location. The previous value is lost.

Figure 2.8. Memory location showing the name and value of variable number1.

When the statement (line 21)

 number2 = input.nextInt(); // read second number from user

executes, suppose that the user enters 72. The computer places that integer value into location number2. The memory now appears as shown in Fig. 2.9.

Figure 2.9. Memory locations after storing values for number1 and number2.

After the program of Fig. 2.7 obtains values for number1 and number2, it adds the values and places the sum into variable sum. The statement (line 23)

 sum = number1 + number2; // add numbers

performs the addition, then replaces sum's previous value. After sum has been calculated, memory appears as shown in Fig. 2.10. Note that the values of number1 and number2 appear exactly as they did before they were used in the calculation of sum. These values were used, but not destroyed, as the computer performed the calculation. Thus, when a valueis read from a memory location, the process is nondestructive.

Figure 2.10. Memory locations after calculating and storing the sum of number1 and number2.

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

Java(c) How to Program
Java How to Program (6th Edition) (How to Program (Deitel))
ISBN: 0131483986
EAN: 2147483647
Year: 2003
Pages: 615 © 2008-2020.
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