Conditional Statements in Java One Page.md

Conditional Statements in Java — ONE PAGE 🎯

A conditional statement allows Java to make a decision based on whether a condition is true or false.

Basic idea

Condition
   ↓
 true / false
   ↓
Choose which statement to execute

Java's main conditional statements are:

1. if
2. if-else
3. else-if ladder
4. nested if
5. switch

---

1. if Statement

Used when you want to execute code only when a condition is true.

Syntax

if (condition) {
    // statements
}

Example

int age = 20;

if (age >= 18) {
    System.out.println("Eligible");
}

Output:

Eligible

If the condition is false, the body is skipped.

---

2. if-else Statement

Used when there are two possible paths.

Syntax

if (condition) {
    // true block
} else {
    // false block
}

Example

int number = 7;

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

Output:

Odd

Remember

true  → if block
false → else block

Only one of the two blocks executes.

---

3. else-if Ladder

Used when there are multiple conditions.

Syntax

if (condition1) {
    // block 1
}
else if (condition2) {
    // block 2
}
else if (condition3) {
    // block 3
}
else {
    // default block
}

Example

int marks = 75;

if (marks >= 90) {
    System.out.println("A");
}
else if (marks >= 75) {
    System.out.println("B");
}
else if (marks >= 60) {
    System.out.println("C");
}
else {
    System.out.println("Fail");
}

Output:

B

Important

Java checks from top to bottom.

Once a condition is true, its block executes and the remaining else-if conditions are skipped.

---

4. Nested if

An if statement inside another if statement is called a nested if.

Example

int age = 20;
boolean citizen = true;

if (age >= 18) {

    if (citizen) {
        System.out.println("Eligible");
    }
}

Think:

Outer condition
      ↓
    true
      ↓
Inner condition
      ↓
    true
      ↓
   Execute

---

5. switch

Used when one expression needs to be compared against multiple possible values.

Syntax

switch (expression) {

    case value1:
        // statements
        break;

    case value2:
        // statements
        break;

    default:
        // statements
}

Example

int day = 2;

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");
}

Output:

Tuesday

---

⚠️ Why break in switch?

Without break, execution can continue into the following cases.

Example:

int x = 1;

switch (x) {

    case 1:
        System.out.println("One");

    case 2:
        System.out.println("Two");
}

Output:

One
Two

With:

break;

after case 1, execution leaves the switch.

---

🔥 Conditional Statements Comparison

Statement	Best Used For
if	One condition
if-else	Two alternatives
else-if ladder	Multiple conditions/ranges
Nested if	Condition inside another condition
switch	Multiple fixed choices

---

🧠 Quick Decision

             Need a decision?
                    ↓
          ┌─────────┴─────────┐
          ↓                   ↓
     Conditions            Fixed choices
     /ranges               /known values
          ↓                   ↓
    if / else-if           switch

Easy memory

if → "Is this condition true?"

if-else → "Which of two paths?"

else-if → "Which condition is true?"

nested if → "If this is true, check another condition."

switch → "Which fixed case matches?"