cs ch2

Chapter Overview

• Title: Data and Expressions (Java Software Solutions Foundations of Program Design, 10th Edition)

• Authors: John Lewis, William Loftus

• Copyright: © 2024 Pearson Education, Inc.

Key Concepts Covered

• Character strings

• Primitive data

• Declaration and use of variables

• Expressions and operator precedence

• Data conversions

• Accepting input from the user

Detailed Breakdown

Character Strings

• Definition: A string literal is enclosed in double quotes.

  • Example:

    • "This is a string literal."

    • "123 Main Street"

    • "X"

• String Class: Every character string is an object defined by the String class in Java.

• String Literal: Each string literal creates a String object.

The println Method

• Usage: Invokes the println method to print output; it advances to the next line after printing.

• Example:System.out.println("Whatever you are, be a good one.");

  • Object: System.out

  • Method: println

  • Parameters: Information to print.

The print Method

• Functionality: Similar to println, but does not advance to the next line.

• Example Code: Countdown program demonstrates this difference.

• Key Point: Output following print appears on the same line.

String Concatenation

• Operator: + is used to concatenate strings and append numbers.

  • Example:

  • "Peanut butter " + "and jelly"

• Limitations: String literals cannot span multiple lines within the program.

Assignment and Initialization

Variables

• Definition: A variable is a memory location name that holds a value.

• Declaration: Specifies variable name and data type.

  • Example: int total;

• Initialization: Assigning an initial value during declaration, e.g., `int sum = 0;

  • Multiple variables can be declared at once, like int count, temp, result;.

Assignment Statement

• Changes the value of a variable using the = operator.

  • Example: total = 55;

• Restrictions: Value assigned must match variable's declared type.

Constants

• Definition: Identifier that holds a constant value throughout.

• Declaration: Use final modifier, e.g., final int MIN_HEIGHT = 69;

• Purpose:

  1. Clarifies literal values.

  2. Eases program maintenance by setting values in one place.

  3. Prevents inadvertent changes to variable.

Primitive Data Types

• Categories:

  • Integers: byte, short, int, long

  • Floating-point: float, double

  • Characters: char

  • Boolean values: boolean

• Size and Value Details: Numeric types vary in size and range.

Expressions

• Definition: Combination of operators and operands.

• Operators: Includes arithmetic operations and evaluations.

• Operator Precedence: Determines evaluation order, with multiplication and division having higher precedence than addition.

Data Conversion

• Purpose: To handle different data types conveniently.

• Types of Conversion:

  • Widening Conversion: Safe conversion from smaller to larger types.

  • Narrowing Conversion: Risks loss of information, converting larger to smaller types.

  • Methods: Assignment, promotion, casting procedures.

Using the Scanner Class

• Utility: Facilitates reading user input conveniently from various sources, including keyboard.

• Example: Declaring a Scanner to read input and methods to capture various data types.

  • Example Usage in Code:

    Scanner scan = new Scanner(System.in);

Interactive Programs

• Input Reading: Utilize Scanner to obtain user input and print results.

  • Example: Reading miles and gallons for calculations (GasMileage program).

Summary of Chapter 2

• Focused on foundational programming concepts, including character strings, primitive data types, variables, expressions, and user input.