1.3. Java Fundamentals¶

1.3.1. Objectives¶

write a java class that includes fields, member methods, and invokes imported code
develop java code with programming constructs such as if statements, for loops, or while loops
trace variables and understand scope
distinguish between primitive types and reference types
run a java program in eclipse
review object Oriented Programming
Explore Enum Types
Explore Switch Statements
Interpret UML diagrams

Suggested Reading: AppendicesB(Java Basics) and C(Classes) from Data Structures and Abstractions with Java, 4th edition by Frank M. Carrano and Timothy Henry

1.3.2. Interactive: Java Basics¶

Follow Along and Engage

Download the slides corresponding to the video. Take notes on them as you watch the video, practice drawing diagrams yourself!

JavaFundamentalsWelcome.pdf

1.3.2.1. Some Java Basics To Be Familiar With¶

Primitive types, Objects or reference types, wrappers, type casting
Java key words
Assignment statements
Expressions, order of operations ++, –
Conditionals such as if, if else, nested conditionals and switch
Loops such as while and for loops
Strings methods
Import statements
Writing and using own methods, scope
Enumerated types
Classes, fields, member methods

Addtional Reference:

Oracle Java Tutorial

1.3.3. Java Methods¶

For the following discussion, we’re going to be referencing the following Bank class:

The Bank Class

import java.util.Scanner;
import java.text.DecimalFormat;

public class Bank {

   static long accountID;
   static String accountHolder;
   static double accountBalance;
   static String PIN;
   static final double withdrawalTransactionCharge = 0.50; // $0.50 charge for
                                                           // each transaction
   private static DecimalFormat df = new DecimalFormat("#.##");

   public enum Choice{
       DEPOSIT, WITHDRAW, DISPLAY, EXIT
   }

   public Bank() {
     init();
   }

   public static void init() {
       accountHolder = "J. Doe";
       accountBalance = 500.00;
       accountID = 555444333;
       PIN = "1234";
   }


   public static void withdraw(double amount) {
       if ((amount + withdrawalTransactionCharge) < accountBalance) {
           accountBalance = accountBalance - amount
               - withdrawalTransactionCharge;
           System.out.println("withdrawing $" + df.format(amount));
       }
       else {
           System.out.println(
               "low account balance, cannot complete withdrawal transaction");
       }
       displayAccountBalance();

   }


   public static void deposit(double amount) {

       accountBalance = accountBalance + amount;
       System.out.println("depositing $" + df.format(amount));
       displayAccountBalance();

   }


   public static void displayMenu() {

       StringBuilder buffer = new StringBuilder();

       buffer.append("*****Welcome to ABC Bank*****");
       buffer.append("\n");
       buffer.append("\n");
       buffer.append("1: Withdraw $20.00");
       buffer.append("\n");
       buffer.append("2: Deposit  $20.00");
       buffer.append("\n");
       buffer.append("3: Display Balance");
       buffer.append("\n");
       buffer.append("\n");
       buffer.append(
           "Please enter your choice of 1, 2, or 3, and press the Enter key");
       buffer.append("\n");
       System.out.println(buffer.toString());
   }


   public static void displayAccountBalance() {

       StringBuilder buffer = new StringBuilder();

       buffer.append("-----Account Details----- ");
       buffer.append("\n");
       buffer.append("Account ID: ");
       buffer.append(accountID);
       buffer.append("\n");
       buffer.append("Holder: ");
       buffer.append(accountHolder);
       buffer.append("\n");
       buffer.append("Balance: $");
       buffer.append(df.format(accountBalance));
       buffer.append("\n");
       buffer.append("-------------------------");
       buffer.append("\n");
       buffer.append("-------------------------");
       buffer.append("\n");
       buffer.append("\n");
       System.out.println( buffer.toString());

   }// end of displayAccountDetails Method


   public static void main(String[] args) {
       init(); // Initializes this account
       displayMenu();

       String response = new Scanner(System.in).nextLine(); // Read user input

       if (response.equals("1")) {
           withdraw(20.00);
       }
       else if (response.equals("2")) {
           deposit(20.00);
       }
       else if (response.equals("3")) {
           displayAccountBalance();
       }
       else {
           System.out.println("You entered an invalid choice.");
       }



       System.out.println("Thank you for banking with us, goodbye!");
   }

}

1.3.3.1. Interactive: Java Methods¶

Correction to the video!

A double can also be thought of as float (not long) https://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html

1.3.4. Checkpoint 1¶

1.3.5. Interactive: Java Variables¶

Follow Along and Engage

Download the slides corresponding to the video. Take notes on them as you watch the video, practice drawing diagrams yourself!

JavaVariables.pdf

1.3.5.1. Decimal Formatting¶

The java.text.DecimalFormat class provides the functionality to format the output of real numbers. For example in the example Bank.java, the df field is declared:

private static DecimalFormat df = new DecimalFormat("0.00");

So throughout the class the DecimalFormat object can be used to format numbers as Strings. For example:

System.out.println("withdrawing $" + df.format(amount));

buffer.append(df.format(accountBalance));

Notice that the following formatting can also be used, but it doesn’t append leading or trailing zeros:

private static DecimalFormat df = new DecimalFormat("#.##");

For more details about Decimal Format, reference: https://docs.oracle.com/javase/tutorial/i18n/format/decimalFormat.html.

1.3.6. Checkpoint 2¶

1.3.7. Interactive: Java Control Flow¶

Follow Along, Practice and Explore

Download to run and explore the java file (see below) from the video on your own in eclipse. You may download the standalone *.java file for this example. To run the standalone *.java file you will need to

create a new Eclipse project, then

create a package within the project called “example” (the package named at the top of the class MUST match the package the file is placed in within the Eclipse project), and finally

download and import the standalone *.java file(s) to the created package.

FridgeInventory.java

1.3.8. Checkpoint 3¶

1.3.9. Interactive: Java Scope and Equality¶

Follow Along and Engage

Download the slides corresponding to the video. Take notes on them as you watch the video, practice drawing diagrams yourself!

JavaFundamentalsTips.pdf

1.3.10. Checkpoint 4¶

1.3.11. Java Objects and Enum¶

1.3.11.1. Java Enums¶

Enum types provide a type which can be assigned a predefined set of constant values. The use of an enum type provides a bounded set of constant values compared to Strings and a more descriptive and readable set of values compared to integers. For example instead of using the numbers 1 through 7 for days of the week, we could declare:

public enum Day {
         SUNDAY, MONDAY, TUESDAY, WEDNESDAY,
         THURSDAY, FRIDAY, SATURDAY
      }

An enum type can be in its own file or nested inside another class. They should be used when you know all the possible values at compile time. For example months of the year, directions on a compass, choices in a menu, or locations in a game. Enum types can improve type safety especially when a parameter to a method is an enum type. Enum types can be compared with the == operator and switch statements.

For more details about enum types, reference: https://docs.oracle.com/javase/tutorial/java/javaOO/enum.html.

We’ll be using enum types together with switch statements (which are discussed below) to experiment with Bank.java

1.3.11.2. Switch Statements¶

Switch statements can be used to control the flow of execution based on multiple possible values of a variable. They are often used with enum types but can also be used with some primitive types, such as int and char, or Strings and some Wrapper classes as well, such as Integer and Character.

Switch statements can be used instead of a series of if statements or nested if-else statements. For example, in the Bank.java code…

if (response.equals("1")) {
   withdraw(20.00);
}
else if (response.equals("2")) {
    deposit(20.00);
}
else if (response.equals("3")) {
    displayAccountBalance();
}
else {
    System.out.println("You entered an invalid choice.");
}

could be replaced with:

switch (response) {
   case "1":
       withdraw(20.00);
       break;
   case "2":
       deposit(20.00);
       break;
   case "3":
       displayAccountBalance();
       break;
   default:
       System.out.println("You entered an invalid choice.");
 }

Notice that in this example each case includes a break statement. Without the break statement the additional lines of code in the switch statement would execute.

Given the following enumerated type:

public enum Day {
         SUNDAY, MONDAY, TUESDAY, WEDNESDAY,
         THURSDAY, FRIDAY, SATURDAY
      }

An example switch statement could be:

switch(today) {
    case SATURDAY:
      System.out.println("Stores are crowded today");
      break;
    case MONDAY:
    case TUESDAY:
       System.out.println("Stores are stocked up today");
       break;
    case WEDNESDAY:
       System.out.println("It's double coupon day");
    default:
       System.out.println("Happy shopping!");
}

Notice that when today is MONDAY it will fall through to the code for the TUESDAY case. When today is WEDNESDAY it will print It’s double coupon day and fall through to also print the default message.

For more details about switch statements, reference: https://docs.oracle.com/javase/tutorial/java/nutsandbolts/switch.html.

Software Design and Data Structures

Chapter 1 Introduction

1.3. Java Fundamentals¶

1.3.1. Objectives¶

1.3.2. Interactive: Java Basics¶

1.3.2.1. Some Java Basics To Be Familiar With¶

1.3.3. Java Methods¶

1.3.3.1. Interactive: Java Methods¶

1.3.4. Checkpoint 1¶

1.3.5. Interactive: Java Variables¶

1.3.5.1. Decimal Formatting¶

1.3.6. Checkpoint 2¶

1.3.7. Interactive: Java Control Flow¶

1.3.8. Checkpoint 3¶

1.3.9. Interactive: Java Scope and Equality¶

1.3.10. Checkpoint 4¶

1.3.11. Java Objects and Enum¶

1.3.11.1. Java Enums¶

1.3.11.2. Switch Statements¶

1.3.11.3. Interactive: Java Objects and Enum¶