Java Module 002: Week 2 - Control Flow (Conditionals)

This module covers Java's conditional control flow constructs, including if, else if, else, nested conditionals, and switch statements. Designed for beginners building on Week 1, it includes explanations, code examples, and practice exercises for each day of Week 2 in the 3-month Java fundamentals plan. By the end, you'll be able to write programs that make decisions based on conditions and create a quiz program as a mini-project.

Day 1: `if`, `else if`, `else` Statements

Objective: Learn to use if, else if, and else for basic decision-making.

Explanation

Conditional Statements: Control program flow based on conditions.
if Statement: Executes code if a condition is true.
- Syntax: if (condition) { // code }
else if: Checks additional conditions if the previous if is false.
else: Executes code if no conditions are true.
Conditions use comparison (==, !=, >, <, etc.) and logical operators (&&, ||, !).

Code Example

public class IfExample {
    public static void main(String[] args) {
        int number = 15;
        
        if (number > 0) {
            System.out.println(number + " is positive");
        } else if (number < 0) {
            System.out.println(number + " is negative");
        } else {
            System.out.println(number + " is zero");
        }
    }
}

Practice

Write a program to check if a number is positive, negative, or zero.
Create a program to determine if a person can vote (age >= 18).
Use else if to categorize a score: excellent (90+), good (70-89), or fail (<70).

Practice Code:

public class IfPractice {
    public static void main(String[] args) {
        int score = 85;
        
        if (score >= 90) {
            System.out.println("Excellent");
        } else if (score >= 70) {
            System.out.println("Good");
        } else {
            System.out.println("Fail");
        }
    }
}

Day 2: Nested `if` Statements

Objective: Understand and use nested if statements for complex conditions.

Explanation

Nested if: An if statement inside another if or else block.
Used for multi-level decision-making.
Example: Check if a number is positive, then check if it’s even.
Avoid excessive nesting for readability; use logical operators when possible.

Code Example

public class NestedIfExample {
    public static void main(String[] args) {
        int number = 24;
        
        if (number > 0) {
            System.out.println(number + " is positive");
            if (number % 2 == 0) {
                System.out.println(number + " is even");
            } else {
                System.out.println(number + " is odd");
            }
        } else {
            System.out.println(number + " is not positive");
        }
    }
}

Practice

Write a program to categorize age: child (<13), teen (13-19), adult (20+).
Add a nested check to see if an adult is a senior (60+).
Rewrite one practice using logical operators instead of nesting (e.g., age >= 13 && age <= 19 for teen).

Practice Code:

public class NestedIfPractice {
    public static void main(String[] args) {
        int age = 65;
        
        if (age < 13) {
            System.out.println("Child");
        } else if (age <= 19) {
            System.out.println("Teen");
        } else {
            System.out.println("Adult");
            if (age >= 60) {
                System.out.println("Senior");
            }
        }
    }
}

Day 3: `switch` Statement

Objective: Use switch for multi-option decision-making.

Explanation

Switch Statement: Selects code to execute based on a variable’s value.

Syntax:

switch (variable) {
    case value1: // code; break;
    case value2: // code; break;
    default: // code;
}

break: Exits the switch block.
default: Executes if no case matches.
Best for discrete values (e.g., integers, strings).

Code Example

public class SwitchExample {
    public static void main(String[] args) {
        int day = 3;
        
        switch (day) {
            case 1:
                System.out.println("Monday");
                break;
            case 2:
                System.out.println("Tuesday");
                break;
            case 3:
                System.out.println("Wednesday");
                break;
            default:
                System.out.println("Invalid day");
        }
    }
}

Practice

Write a program to print day names based on numbers (1-7).
Create a program to assign grades (A, B, C, etc.) based on a score range (e.g., 90-100 = A).
Add a default case to handle invalid inputs.

Practice Code:

public class SwitchPractice {
    public static void main(String[] args) {
        char grade = 'B';
        
        switch (grade) {
            case 'A':
                System.out.println("Excellent");
                break;
            case 'B':
                System.out.println("Good");
                break;
            case 'C':
                System.out.println("Average");
                break;
            default:
                System.out.println("Invalid grade");
        }
    }
}

Day 4: Combining `if` and `switch`

Objective: Combine conditionals for menu-driven programs.

Explanation

Use if and switch together for flexible decision-making.
Example: Use if to validate input, then switch to handle options.
Ensures robust programs by checking conditions before switching.

Code Example

public class MenuExample {
    public static void main(String[] args) {
        int choice = 2;
        
        if (choice >= 1 && choice <= 3) {
            switch (choice) {
                case 1:
                    System.out.println("Start Game");
                    break;
                case 2:
                    System.out.println("Load Game");
                    break;
                case 3:
                    System.out.println("Exit");
                    break;
            }
        } else {
            System.out.println("Invalid choice");
        }
    }
}

Practice

Create a menu-driven program with options (e.g., 1: Add, 2: Subtract, 3: Exit).
Use if to validate the choice before processing with switch.
Add a message for invalid inputs.

Practice Code:

public class MenuPractice {
    public static void main(String[] args) {
        int operation = 1;
        int a = 10, b = 5;
        
        if (operation >= 1 && operation <= 3) {
            switch (operation) {
                case 1:
                    System.out.println("Add: " + (a + b));
                    break;
                case 2:
                    System.out.println("Subtract: " + (a - b));
                    break;
                case 3:
                    System.out.println("Exit");
                    break;
            }
        } else {
            System.out.println("Invalid operation");
        }
    }
}

Day 5: Review and Edge Cases

Objective: Solidify conditionals and handle edge cases.

Explanation

Edge Cases: Unexpected inputs (e.g., negative numbers, zero, invalid types).
Use conditionals to validate inputs and prevent errors.
Example: Check if input is within a valid range before processing.

Code Example

public class EdgeCaseExample {
    public static void main(String[] args) {
        int score = -10;
        
        if (score < 0 || score > 100) {
            System.out.println("Invalid score: must be between 0 and 100");
        } else if (score >= 90) {
            System.out.println("Grade: A");
        } else if (score >= 70) {
            System.out.println("Grade: B");
        } else {
            System.out.println("Grade: C or below");
        }
    }
}

Practice

Write a program to validate a test score (0-100) and assign a grade.
Handle edge cases (negative scores, scores > 100).
Combine if and switch to process a validated input.

Practice Code:

public class EdgeCasePractice {
    public static void main(String[] args) {
        int score = 95;
        
        if (score < 0 || score > 100) {
            System.out.println("Invalid score");
        } else {
            char grade;
            if (score >= 90) grade = 'A';
            else if (score >= 70) grade = 'B';
            else grade = 'C';
            
            switch (grade) {
                case 'A':
                    System.out.println("Excellent");
                    break;
                case 'B':
                    System.out.println("Good");
                    break;
                case 'C':
                    System.out.println("Needs Improvement");
                    break;
            }
        }
    }
}

Weekend: Review and Mini-Project

Objective: Consolidate Week 2 learning with a quiz program.

Review

Revisit:
- if, else if, else for decision-making.
- Nested if for multi-level conditions.
- switch for discrete options.
- Combining conditionals and handling edge cases.
Debug common errors (e.g., missing break in switch, incorrect conditions).

Mini-Project: Simple Quiz Program

Create a console-based quiz program that:

Asks a multiple-choice question (e.g., "What is 2 + 2? A: 3, B: 4, C: 5").
Uses char or String for user input (e.g., 'A', 'B', 'C').
Validates input with if (e.g., ensure input is A, B, or C).
Uses switch to check the answer and print feedback.
Handles invalid inputs (e.g., 'D') with a default message.

Project Code:

public class QuizProgram {
    public static void main(String[] args) {
        char answer = 'B'; // Simulate user input
        
        // Validate input
        if (answer == 'A' || answer == 'B' || answer == 'C') {
            System.out.println("Question: What is 2 + 2?");
            System.out.println("A: 3, B: 4, C: 5");
            
            switch (answer) {
                case 'A':
                    System.out.println("Incorrect. The answer is 4.");
                    break;
                case 'B':
                    System.out.println("Correct! 2 + 2 = 4.");
                    break;
                case 'C':
                    System.out.println("Incorrect. The answer is 4.");
                    break;
            }
        } else {
            System.out.println("Invalid answer. Please choose A, B, or C.");
        }
    }
}

Weekend Practice

Run and test the quiz program with different inputs.
Add a second question with different options.
Modify the program to track a score (e.g., +1 for correct, 0 for incorrect).

Tips for Week 2

Practice: Test each code example in an IDE or terminal.
Debug: Watch for missing break statements in switch or incorrect logical conditions.
Resources: Refer to Oracle’s Java Tutorials or W3Schools for control flow details.
Experiment: Modify code to test different conditions and edge cases.

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Java Module 002: Week 2 - Control Flow (Conditionals)

Day 1: `if`, `else if`, `else` Statements

Explanation

Code Example

Practice

Day 2: Nested `if` Statements

Explanation

Code Example

Practice

Day 3: `switch` Statement

Explanation

Code Example

Practice

Day 4: Combining `if` and `switch`

Explanation

Code Example

Practice

Day 5: Review and Edge Cases

Explanation

Code Example

Practice

Weekend: Review and Mini-Project

Review

Mini-Project: Simple Quiz Program

Weekend Practice

Tips for Week 2

FilesExpand file tree

java_module_002.md

Latest commit

History

java_module_002.md

File metadata and controls

Java Module 002: Week 2 - Control Flow (Conditionals)

Day 1: if, else if, else Statements

Explanation

Code Example

Practice

Day 2: Nested if Statements

Explanation

Code Example

Practice

Day 3: switch Statement

Explanation

Code Example

Practice

Day 4: Combining if and switch

Explanation

Code Example

Practice

Day 5: Review and Edge Cases

Explanation

Code Example

Practice

Weekend: Review and Mini-Project

Review

Mini-Project: Simple Quiz Program

Weekend Practice

Tips for Week 2

Day 1: `if`, `else if`, `else` Statements

Day 2: Nested `if` Statements

Day 3: `switch` Statement

Day 4: Combining `if` and `switch`