Chap02

Chapter Overview

• Elementary Programming: Covering essentials of programming in Java, moving from simple program execution to solving practical problems.

Motivations

• Building on knowledge from previous chapters:

  • Creating, compiling, and running Java programs.

• New focus on solving practical problems programmatically:

  • Understanding Java data types, operators, expressions, input/output.

Objectives

Key Learning Outcomes

• Writing Java programs for basic calculations.

• Using the Scanner class for console input.

• Utilizing identifiers for naming variables, constants, and other methods.

• Controlling data storage with variables and constants.

• Implementing assignment statements and expressions.

• Exploring Java’s primitive data types:

  • byte, short, int, long, float, double, char.

• Applying operators for numeric expressions.

• Displaying time and using shorthand operators.

• Understanding type casting for different value types.

• Computing values like loan payments and monetary changes.

• Engaging with Java documentation and programming conventions.

• Differentiating between syntax, runtime, and logic errors; debugging techniques.

Example Program: Compute the Area of a Circle

Program Code Overview

public class ComputeArea {
  public static void main(String[] args) {
    double radius;
    double area;
    radius = 20;
    area = radius * radius * 3.14159;
    System.out.println("The area for the circle of radius " + radius + " is " + area);
  }
}

Execution Trace

• Memory Allocation:

  • Variables (radius, area): No initial values.

• Radius Assignment:

  • radius is assigned a value of 20.

• Area Calculation:

  • Area computed and stored using the formula.

  • Output: "The area for the circle of radius 20 is 1256.636".

Reading Input from the Console

Steps to Use Scanner

1. Create Scanner Object: Scanner input = new Scanner(System.in);

2. Input Methods: Use next() options for different data types (e.g., nextInt() for integers).

   • Example: double d = input.nextDouble();

Identifiers

• Definition: Sequence of characters (letters, digits, underscores, $).

• Rules for Identifiers:

  • Must start with a letter, underscore, or dollar sign.

  • Cannot start with a digit.

  • Cannot be a reserved word.

  • Can be of any length.

Variables

• Variable Declaration and Assignment:

  • Example Calculations:

    • Area calculation using different radius values (e.g., 1.0, 2.0).

Declaring Variables

• Example Declarations:

  • int x; // integer variable

  • double radius; // double variable

  • char a; // character variable

Assignment Statements

• Assign values to variables:

  • x = 1;

  • radius = 1.0;

  • a = 'A';

Constants

• Definition: Values that should not change.

Numerical Data Types

• Data Type Ranges and Sizes:

  • byte: -128 to 127 (8-bit)

  • short: -32768 to 32767 (16-bit)

  • int: -2147483648 to 2147483647 (32-bit)

  • long: -9223372036854775808 to 9223372036854775807 (64-bit)

  • float and double: Various ranges per IEEE standards.

Numeric Operators

• Basic Operators:

  • + Addition, - Subtraction, * Multiplication, / Division, % Remainder.

Integer Division

• Division Examples:

  • 5 / 2 yields 2 (integer).

  • 5.0 / 2 yields 2.5 (double).

Remainder Operator

• Used for determining even/odd numbers:

  • Example: number % 2.

Floating-Point Precision

• Important Note: Floating-point numbers may not store exact values.

  • Example: Calculation nuances with 1.0 - 0.1.

Number Literals

• Definition: Constant values in code (e.g., 34, 5.0).

Integer Literals

• Must fit data type limits to avoid errors (e.g., byte b = 1000;).

Floating-Point Literals

• By default treated as double; append f for float (e.g., 5.0f).

Scientific Notation

• Floating-point literals in scientific notation (e.g., 1.23456e+2).

Arithmetic Expressions

• Syntax examples to evaluate: 3 + 4 * 10.

Problem: Temperature Conversion

Task

• Convert Fahrenheit to Celsius with a formula.

Current Time Display Problem

• Displays time in GMT using currentTimeMillis() method.

Shortcut Assignment Operators

• Examples: i += 8 is equivalent to i = i + 8.

Increment/Decrement Operators

• Shorter forms to modify values (e.g., ++var, var--).

Assignment Expressions

• Allowed expressions for statements post Java 2.

Numeric Type Conversion Rules

• Automatic type conversions during binary operations based on operand types.

Type Casting

• Implicit (widening) and Explicit (narrowing) casting rules.

Keeping Decimal Points Program

• Program requires precision in tax rounding.

Loan Payments Program

• User input for calculating monthly and total payments.

Character Data Type

• Uses char for ASCII representations; Unicode compatibility.

Unicode Format

• Utilizes 16-bit encoding for text representation across languages.

Escape Sequences

• Special characters denoted with escape sequences (e.g., \, ).

ASCII Character Set

• Covering encoding in both decimal and hexadecimal indices.

Casting between char and Numeric Types

• Example conversions between char and int.

Monetary Units Problem

• Program converts decimal input into monetary equivalents.

String Type

• Use String for multiple characters; reference type.

String Concatenation

• Examples of how strings combine.

Programming Style Guidelines

Comments

• Summarize program function and details.

Naming Conventions

• Use meaningful names following Java conventions.

Indentation/Spacing

• Recommend practices for readability.

Block Styles

• Different styles for coding blocks.

Programming Errors

Types of Errors

• Syntax: Caught by compiler.

• Runtime: Program crashes.

• Logic: Incorrect program outputs.

Debugging Techniques

• Methods for identifying bugs, including print statements and debuggers.

Using JOptionPane for Input

• Two methods for input collection from dialogs.

Input Conversion

• Converting strings to int and double using appropriate methods.