Decision Making in Java – if, else-if, switch, and Nested Conditions

Decision-making statements in Java control the flow of execution based on conditions. They allow programs to behave dynamically depending on runtime values. Understanding if, else-if, switch, and nested conditions is essential for writing flexible and robust code.

---

🔍 Why Decision-Making is Important?

• Allows programs to make choices based on data.
• Used in every real-world Java application.
• Critical for implementing algorithms and user-driven logic.
• Frequently asked in Java interviews.

---

✅ if Statement

The if statement executes a block of code only when the condition is true.

✅ Syntax:

if(condition) {
    // Code executes if condition is true
}

✅ Example:

int age = 20;
if(age >= 18) {
    System.out.println("You are eligible to vote.");
}

---

✅ if-else Statement

The if-else statement provides an alternative block when the condition is false.

✅ Example:

int number = 5;
if(number % 2 == 0) {
    System.out.println("Even");
} else {
    System.out.println("Odd");
}

---

✅ else-if Ladder

When multiple conditions need to be checked sequentially, we use an else-if ladder.

✅ Example:

int marks = 75;
if(marks >= 90) {
    System.out.println("Grade A");
} else if(marks >= 75) {
    System.out.println("Grade B");
} else {
    System.out.println("Grade C");
}

---

✅ switch Statement

The switch statement is used when multiple possible execution paths are based on a single variable or expression.

✅ Syntax:

switch(expression) {
    case value1:
        // Code block
        break;
    case value2:
        // Code block
        break;
    default:
        // Code block
}

✅ Example:

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");
}

---

✅ Nested if Statements

You can place if statements inside other if statements for complex conditions.

✅ Example:

int age = 25;
boolean hasID = true;

if(age >= 18) {
    if(hasID) {
        System.out.println("Access granted");
    } else {
        System.out.println("ID required");
    }
} else {
    System.out.println("Underage");
}

---

🔄 Performance & When to Use

• if-else is better for fewer conditions or range checks.
• switch is efficient when comparing a single variable against multiple values.
• Use nested ifs only when logic requires multiple dependent conditions.
• Java 7+ allows String in switch.
• Java 14+ introduced switch expressions with yield.

---

🚫 Common Mistakes

• Forgetting break in switch cases leads to fall-through.
• Using nested ifs without braces, making code hard to maintain.
• Overusing nested conditions instead of refactoring into methods.

---

💡 Tips & Best Practices

• Keep conditions readable and simple.
• Use switch for discrete values; use if-else for ranges.
• Always include default in switch.
• Prefer enums in switch for type safety.

---

🧠 Interview Relevance

• Q: Difference between if-else and switch?

• A: if-else is flexible for ranges; switch is faster for discrete values.

• Q: Can we use Strings in switch?

• A: Yes, Java 7+ supports Strings in switch.

---

🧩 Java Version Relevance

Java Version	Feature
Java 1.0	Basic if-else and switch statements
Java 7	Added String support in switch
Java 14	Introduced switch expressions

---

✅ Summary

• if: For simple conditions.
• if-else: For binary choices.
• else-if: For multiple ranges.
• switch: For comparing discrete values.
• nested if: For dependent checks.

---