☕ Java📅 Day 6

Conditional Statements in Java

if, if-else, else-if ladder, nested if, and switch statements in Java.

🎯

Learning objectives

→Write branching logic using if / else-if / else
→Choose between if-else ladder and switch
→Use switch expressions (Java 14+) for concise code

💡 Key points

Condition must evaluate to boolean — Java rejects `if (1)` (unlike C).
if-else-if runs top to bottom, stops at first true branch.
switch works with int, char, String, enum — from Java 14+, also as an expression.
Braces are optional for single statement but always use them — safer.

💻 Code examples(4)

#1if / else if / else

java

int marks = 72;
if (marks >= 90) {
    System.out.println("A+");
} else if (marks >= 75) {
    System.out.println("A");
} else if (marks >= 60) {
    System.out.println("B");
} else {
    System.out.println("Needs work");
}

Output

First branch that evaluates to true wins. Order matters — put stricter conditions first.

#2Classic switch

java

int day = 3;
switch (day) {
    case 1:  System.out.println("Mon"); break;
    case 2:  System.out.println("Tue"); break;
    case 3:  System.out.println("Wed"); break;
    default: System.out.println("Other");
}

Output

Wed

break stops fall-through. Miss a break → execution continues into the next case (common bug).

#3Switch expression (Java 14+)

java

String name = switch (day) {
    case 1 -> "Mon";
    case 2 -> "Tue";
    case 3 -> "Wed";
    default -> "Other";
};

Arrow form — no break needed, returns a value, safer. Modern preferred style.

#4Nested if

java

int age = 20;
boolean hasId = true;
if (age >= 18) {
    if (hasId) {
        System.out.println("Allowed");
    } else {
        System.out.println("ID required");
    }
}

Combine with && when possible: if (age >= 18 && hasId). Flatter is cleaner.

🎯 Practice

Q1. Will `if (x = 5)` compile in Java?+

No. `x = 5` is assignment returning int, but if requires boolean. Java catches this at compile time (unlike C).

Q2. What happens if you omit break in a switch case?+

Fall-through — execution continues into the next case until it hits a break or the switch ends.

Q3. Rewrite using ternary: if (x > 0) sign = 1; else sign = -1;+

int sign = (x > 0) ? 1 : -1;

📝 Notes

When to prefer switch over if-else

Use switch when comparing a single variable against many constant values (day names, menu options, enum states). Use if-else when conditions involve ranges (marks >= 60) or multiple variables.

Common trap

if (score = 100) { ... }   // ❌ won't compile in Java
if (score == 100) { ... }  // ✅ correct

Java saves you here — same bug in C/C++ silently passes.