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Activity 1.8 Intermediate Data Types and Operations

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Introduction

Activity 1.8

Intermediate Data Types and Operations

Topics

  • Escape Sequences
  • Constants
  • Type Casting
  • Compound Assignment Operators
  • Increment and Decrement Operators
  • The Math Class

Escape Sequences

An escape sequence is a special combination of characters that tells a computer to do something other than what those characters normally do.

In Java, an escape sequence starts with a backslash (\) followed by another character.

For example, the sequence \n doesn't print a backslash and the letter 'n'. Instead, the backslash "escapes" the usual meaning of the 'n' and tells the program to insert a new line.

Escape Sequences

  • \n Newline
  • \\ Backslash literal
  • \" Double-Quote literal
  • \t Tab
  • \' Single-Quote literal

Constants

A constant is a variable whose value, once assigned, cannot be changed. It's used to store data that should remain the same throughout a program's execution.

Constants

You define a constant using the final keyword. The convention is to name constants using all uppercase letters, with words separated by underscores. 

final double TAX_RATE = 0.08;
...
double total = subtotal * TAX_RATE;

Why Use Constants

Readability: Using a descriptive name like PI or MAX_CONNECTIONS is much clearer than using a "magic number" like 3.14159 or 100.

Preventing Errors: Since the value can't be changed after initialization, you're protected from accidentally overwriting it later in your code.

Type Casting

The process of explicitly converting a value from one data type to another. For the AP Computer Science A exam, this involves:

Narrowing (double -> int)
This truncates (cuts off) any decimal portion of the number.
Widening (int -> double)
This is often done to ensure that a calculation (especially division) produces a decimal result rather than an integer.

Type Casting

Narrowing
double myDouble = 7.99;
int myInt = (int) myDouble; // myInt becomes 7
Widening
int a = 5;
int b = 2;
double result = (double) a / b; // The cast ensures floating-point division
// The expression is evaluated as 5.0 / 2, and the result is 2.5

Compound Assignment Operators

Compound assignment operators provide a concise way to perform an operation on a variable and then assign the new value back to that same variable.

+= -= *= /= %=
Addition Assignment: x = x + 5 -> x += 5
Subtraction Assignment: x = x - 5 -> x -= 5
Multiplication Assignment: y = y * 2 -> y *= 2
Divison Assignment: y = y / 2 -> y /= 2
Modulus Assignment: y = y % 2 -> y %= 2

Increment and Decrement Operators

The increment (++) and decrement (--) operators are a shorthand way to add or subtract 1 from a variable. These are frequently used in loops and counters. There are two forms for each operator: prefix form and postfix form.

Increment and Decrement Operators

Prefix Form

Prefix Form (++x or --x): The operator comes before the variable. The value is incremented or decremented first, and then the new value is used in the expression. 

int x = 5;
int y = ++x; // Prefix increment
// x is incremented to 6, then assigned to y. Both x and y are now 6.

Increment and Decrement Operators

Postfix Form

Postfix Form (x++ or x--): The operator comes after the variable. The original value is used in the expression first, and then the value is incremented or decremented. 

int a = 5;
int b = a++; // Postfix increment
// a's original value (5) is assigned to b. Then, a is incremented to 6. a is 6, b is 5.
int x = 5;
x++; // x is simply incremented to the value 6.

The Math Class

The Math class contains a collection of methods and constants for performing common mathematical operations.

Constants:
Math.PI
Represents the mathematical constant PI (Ď€), approximately 3.14159.
Math.E
Represents the base of the natural logarithm (e), approximately 2.718.

The Math Class

Methods:
Math.abs(num)
Returns the absolute value of num. Example: Math.abs(-10) returns 10.
Math.pow(base, exp)
Returns the value of the base raised to the power of the exp. Example: Math.pow(2, 3) returns 8.0. The return type is a double.

The Math Class

Math.sqrt(num)
Returns the positive square root of num. Example: Math.sqrt(25) returns 5.0. The return type is a double.
Math.min(num1, num2) and Math.max(num1, num2)
Returns the smaller or larger of the two values. Example: Math.min(5, 8) returns 5.

The Math Class

Math.random()
Returns a random double value greater than or equal to 0.0 and less than 1.0 (~0.9999).
Example: (int)(Math.random() * 10) + 1 returns a random integer between 1 and 10 (inclusive).

The Math Class

Math.round(num)
Returns the closest long to the argument. This is used to round a decimal number to the nearest whole number.
Example: Math.round(7.6) returns 8.

'F' → Fullscreen

Objectives

  • icon Practice implementing various Java constructs:
    • icon Escape sequences
    • icon Constants
    • icon Type casting
    • icon Compound assignment operations
    • icon Increment and decrement operations
    • icon Math constants and methods
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Activity Tasks

  • icon Create a new project named 1-8-Intermediate-Data-Operations.
  • icon Complete each task individually.

Task 1: Increment, Decrement, and Compound Assignment

Program.java
import java.util.Scanner;


public class Program {
    public static void main(String[] args) {
        // Scanner is only being used to pause between demos.
        Scanner input = new Scanner(System.in);


        System.out.println("--- Task 1: Increment, Decrement, and Compound Assignment ---");


        int score = 10;
        System.out.println("Initial score: " + score);


        // Compound assignment
        score += 5;
        System.out.println("Score after += 5: " + score);


        // Increment operator
        score++;
        System.out.println("Score after ++: " + score);


        // Decrement operator
        score--;
        System.out.println("Score after --: " + score);


        System.out.print("\nPress enter to continue...");
        input.nextLine();
//
    }
}

Task 2: Type Casting

Program.java
import java.util.Scanner;


public class Program {
    public static void main(String[] args) {
        // Scanner is only being used to pause between demos.
        Scanner input = new Scanner(System.in);


        System.out.println("--- Task 1: Increment, Decrement, and Compound Assignment ---");


        int score = 10;
        System.out.println("Initial score: " + score);


        // Compound assignment
        score += 5;
        System.out.println("Score after += 5: " + score);


        // Increment operator
        score++;
        System.out.println("Score after ++: " + score);


        // Decrement operator
        score--;
        System.out.println("Score after --: " + score);


        System.out.print("\nPress enter to continue...");
        input.nextLine();


        // -----------------------------------------------------------------------------


        System.out.println("--- Task 2: Type Casting ---");


        double price = 29.99;
        System.out.println("Original price (double): " + price);


        // Narrowing conversion (double to int)
        int intPrice = (int) price;
        System.out.println("Price after casting to int: " + intPrice);


        int items = 3;
        // Explicit casting for accurate division
        double average = (double) intPrice / items;
        System.out.println("Average price with explicit casting: " + average);


        System.out.print("\nPress enter to continue...");
        input.nextLine();
//
    }
}

Task 3: The Math Class and Constants

Program.java
import java.util.Scanner;


public class Program {
    public static void main(String[] args) {
        // Scanner is only being used to pause between demos.
        Scanner input = new Scanner(System.in);


        System.out.println("--- Task 1: Increment, Decrement, and Compound Assignment ---");


        int score = 10;
        System.out.println("Initial score: " + score);


        // Compound assignment
        score += 5;
        System.out.println("Score after += 5: " + score);


        // Increment operator
        score++;
        System.out.println("Score after ++: " + score);


        // Decrement operator
        score--;
        System.out.println("Score after --: " + score);


        System.out.print("\nPress enter to continue...");
        input.nextLine();


        // -----------------------------------------------------------------------------


        System.out.println("--- Task 2: Type Casting ---");


        double price = 29.99;
        System.out.println("Original price (double): " + price);


        // Narrowing conversion (double to int)
        int intPrice = (int) price;
        System.out.println("Price after casting to int: " + intPrice);


        int items = 3;
        // Explicit casting for accurate division
        double average = (double) intPrice / items;
        System.out.println("Average price with explicit casting: " + average);


        System.out.print("\nPress enter to continue...");
        input.nextLine();


        // -----------------------------------------------------------------------------


        System.out.println("--- Task 3: The Math Class and Constants ---");


        // Constant declaration
        final double PI = 3.14159;
        int radius = 5;


        // Calculate area using Math.pow()
        double area = PI * Math.pow(radius, 2);
        System.out.println("Area of circle with radius " + radius + ": " + area);


        // Generate a random dice roll (1-6)
        int diceRoll = (int) (Math.random() * 6) + 1;
        System.out.println("Random dice roll: " + diceRoll);


        System.out.print("\nPress enter to continue...");
        input.nextLine();
//
    }
}

Task 4: Escape Sequences

Program.java
import java.util.Scanner;


public class Program {
    public static void main(String[] args) {
        // Scanner is only being used to pause between demos.
        Scanner input = new Scanner(System.in);


        System.out.println("--- Task 1: Increment, Decrement, and Compound Assignment ---");


        int score = 10;
        System.out.println("Initial score: " + score);


        // Compound assignment
        score += 5;
        System.out.println("Score after += 5: " + score);


        // Increment operator
        score++;
        System.out.println("Score after ++: " + score);


        // Decrement operator
        score--;
        System.out.println("Score after --: " + score);


        System.out.print("\nPress enter to continue...");
        input.nextLine();


        // -----------------------------------------------------------------------------


        System.out.println("--- Task 2: Type Casting ---");


        double price = 29.99;
        System.out.println("Original price (double): " + price);


        // Narrowing conversion (double to int)
        int intPrice = (int) price;
        System.out.println("Price after casting to int: " + intPrice);


        int items = 3;
        // Explicit casting for accurate division
        double average = (double) intPrice / items;
        System.out.println("Average price with explicit casting: " + average);


        System.out.print("\nPress enter to continue...");
        input.nextLine();


        // -----------------------------------------------------------------------------


        System.out.println("--- Task 3: The Math Class and Constants ---");


        // Constant declaration
        final double PI = 3.14159;
        int radius = 5;


        // Calculate area using Math.pow()
        double area = PI * Math.pow(radius, 2);
        System.out.println("Area of circle with radius " + radius + ": " + area);


        // Generate a random dice roll (1-6)
        int diceRoll = (int) (Math.random() * 6) + 1;
        System.out.println("Random dice roll: " + diceRoll);


        System.out.print("\nPress enter to continue...");
        input.nextLine();


        // -----------------------------------------------------------------------------


        System.out.println("--- Task 4: Escape Characters ---");


        // Using tab (\t) for formatting
        String table = "Item\t\tPrice\nKeyboard\t$75\nMouse\t\t$25";
        System.out.println(table);


        // Using newline (\n) and quotes (\")
        String message = "He said, \"Hello, world!\"\nAnd the program responded, 'Hi.'";
        System.out.println(message);


        System.out.print("\nPress enter to continue...");
        input.nextLine();
//
    }
}

Task 5: Combining Concepts

Program.java
import java.util.Scanner;


public class Program {
    public static void main(String[] args) {
        // Scanner is only being used to pause between demos.
        Scanner input = new Scanner(System.in);


        System.out.println("--- Task 1: Increment, Decrement, and Compound Assignment ---");


        int score = 10;
        System.out.println("Initial score: " + score);


        // Compound assignment
        score += 5;
        System.out.println("Score after += 5: " + score);


        // Increment operator
        score++;
        System.out.println("Score after ++: " + score);


        // Decrement operator
        score--;
        System.out.println("Score after --: " + score);


        System.out.print("\nPress enter to continue...");
        input.nextLine();


        // -----------------------------------------------------------------------------


        System.out.println("--- Task 2: Type Casting ---");


        double price = 29.99;
        System.out.println("Original price (double): " + price);


        // Narrowing conversion (double to int)
        int intPrice = (int) price;
        System.out.println("Price after casting to int: " + intPrice);


        int items = 3;
        // Explicit casting for accurate division
        double average = (double) intPrice / items;
        System.out.println("Average price with explicit casting: " + average);


        System.out.print("\nPress enter to continue...");
        input.nextLine();


        // -----------------------------------------------------------------------------


        System.out.println("--- Task 3: The Math Class and Constants ---");


        // Constant declaration
        final double PI = 3.14159;
        int radius = 5;


        // Calculate area using Math.pow()
        double area = PI * Math.pow(radius, 2);
        System.out.println("Area of circle with radius " + radius + ": " + area);


        // Generate a random dice roll (1-6)
        int diceRoll = (int) (Math.random() * 6) + 1;
        System.out.println("Random dice roll: " + diceRoll);


        System.out.print("\nPress enter to continue...");
        input.nextLine();


        // -----------------------------------------------------------------------------


        System.out.println("--- Task 4: Escape Characters ---");


        // Using tab (\t) for formatting
        String table = "Item\t\tPrice\nKeyboard\t$75\nMouse\t\t$25";
        System.out.println(table);


        // Using newline (\n) and quotes (\")
        String message = "He said, \"Hello, world!\"\nAnd the program responded, 'Hi.'";
        System.out.println(message);


        System.out.print("\nPress enter to continue...");
        input.nextLine();


        // -----------------------------------------------------------------------------


        System.out.println("--- Task 5: Challenge Task (Combining Concepts) ---");


        int totalStudents = 15;
        final double GRADE_INCREASE = 1.05;
        double newGrade = 80;


        // Compound assignment with a constant
        newGrade *= GRADE_INCREASE;


        // Round the grade using Math.round()
        long roundedGrade = Math.round(newGrade);


        // Print a final, formatted message that includes all variables
        String finalMessage = "Out of " + totalStudents + " students, the new rounded grade is: " + roundedGrade + ".\n\tThis is a " + (GRADE_INCREASE - 1) * 100 + "% increase.";
        System.out.println(finalMessage);
//
    }
}
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Sample Output

Your program output should something similar to the sample output below.

Sample Output
--- Task 1: Increment, Decrement, and Compound Assignment ---
Initial score: 10
Score after += 5: 15
Score after ++: 16
Score after --: 15


Press enter to continue...
--- Task 2: Type Casting ---
Original price (double): 29.99
Price after casting to int: 29
Average price with explicit casting: 9.666666666666666


Press enter to continue...
--- Task 3: The Math Class and Constants ---
Area of circle with radius 5: 78.53975
Random dice roll: 2


Press enter to continue...
--- Task 4: Escape Characters ---
Item            Price
Keyboard        $75
Mouse           $25
He said, "Hello, world!"
And the program responded, 'Hi.'


Press enter to continue...
--- Task 5: Challenge Task (Combining Concepts) ---
Out of 15 students, the new rounded grade is: 84.
        This is a 5.000000000000004% increase.
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Reflection Questions

You may write your reflection answers as comments at the bottom of your code.

  1. Think about the concept of compound assignment. What is a real-world scenario (outside of a programming context) where you might perform a similar "shortcut" operation—where you update a value by combining it with another? For example, is there a situation where you keep a running total of expenses by adding each new cost to your existing total, rather than recalculating from scratch each time?
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Submission

Submit your activity and reflection answers to the appropriate dropbox.

Activity Complete