CONTROL STRUCTURES IN JAVA

🧠 CONTROL STRUCTURES IN JAVA

🧩 What Are Control Structures?

Control structures decide how and when parts of your program are executed.
Without them, your code would just run from top to bottom — no logic, no decisions.

Java has 3 main types of control structures:

1. Selection – decision-making (if, if-else, switch)

2. Repetition – looping (while, do-while, for)

3. Branching – control transfer (break, continue, return)

🧭 1⃣ SELECTION STATEMENTS

Used for decision-making — choosing what to do based on conditions.

🧱 if Statement

Executes a block of code only if a certain condition is true.

Syntax:

if (boolean-expression) {
   statements;
}

Example:

int a = 16;
if (a % 2 == 0) {
   System.out.println("This is an even number");
}

✅ If the condition (a % 2 == 0) is true, the message prints.
🚫 If false, nothing happens.

Real-life analogy:
If it’s raining → bring umbrella ☔
If not → do nothing.

🧱 if-else Statement

Gives you two possible paths — one if true, one if false.

Syntax:

if (condition) {
   statements;
} else {
   statements;
}

Example:

int a = 16;
if (a % 2 == 0) {
   System.out.println("This is an even number");
} else {
   System.out.println("It is an odd number");
}

Shortcut tip:
🧩 “If-else” = choose between two possibilities (like yes/no, pass/fail, etc.)

🎚 switch Statement

Used when you have many possible values for a variable — easier than writing many if-else’s.

Syntax:

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

Example:

int day = 5;
switch (day) {
   case 1: System.out.println("Monday"); break;
   case 2: System.out.println("Tuesday"); break;
   case 3: System.out.println("Wednesday"); break;
   case 4: System.out.println("Thursday"); break;
   case 5: System.out.println("Friday"); break;
   default: System.out.println("Invalid entry");
}

🗓 Output: Friday
Because day = 5.

Notes:

• break stops the execution (or else the next case will run too).

• default runs when no match is found.

• Data type for case must match switch variable.

Real-life analogy:
Parang menu selector — pick 1, 2, or 3 → gets a specific output 🍔🥤🍟

🔁 2⃣ REPETITION STATEMENTS (LOOPS)

Used for repeating tasks without writing the same code many times.

Java has 3 main loops:

• while

• do-while

• for

🌀 while Loop

Repeats code while a condition is true. (Pre-test loop)

Syntax:

while (condition) {
   statement;
}

Example:

int i = 1;
while (i <= 5) {
   System.out.println(i);
   i++;
}

🧩 Output: 1 2 3 4 5
It stops once i becomes 6 (condition false).

Remember: Check condition first → then execute.

🔄 do-while Loop

Similar to while, but this one executes the block at least once before checking the condition. (Post-test loop)

Syntax:

do {
   statement;
} while (condition);

Example:

int j = 1;
do {
   System.out.println(j);
   j++;
} while (j <= 10);

💡 Even if condition is false, the code inside do still runs once!

🔂 for Loop

Used when the number of iterations is known ahead of time.

Syntax:

for (initialization; condition; update) {
   statement;
}

Example:

for (int i = 1; i <= 10; i++) {
   System.out.print(i * i + " ");
}

🧩 Output: 1 4 9 16 25 36 49 64 81 100

Parts Explained:

⚠ Common mistake: Adding a semicolon after for —

for (int i=1; i<=10; i++); // ❌ don’t do this

It makes the loop run incorrectly or skip content!

3 BRANCHING STATEMENTS

Used to jump or transfer control to another part of the program.

🚪 break Statement

Ends a loop or switch immediately.

Example:

for (int i = 1; i <= 10; i++) {
   if (i == 5) {
      break;
   }
   System.out.println(i);
}

🧩 Output: 1 2 3 4
→ It stops when i == 5.

Used in:

• switch statements

• for, while, and do-while loops

⏭ continue Statement

Skips the current loop iteration and moves to the next one.

Example:

for (int i = 1; i <= 5; i++) {
   if (i == 3) {
      continue;
   }
   System.out.println(i);
}

🧩 Output: 1 2 4 5
(It skipped 3)

🔙 return Statement

Ends the method and optionally sends a value back to the caller.

Syntax:

return value;     // returns a value
return;           // returns nothing (for void methods)

Example:

public static void hello() {
   System.out.println("Hello " + welcome());
}

static String welcome() {
   return "Welcome to Java Programming";
}

🧩 Output: Hello Welcome to Java Programming

In short:

• return → exits a method.

• return value → gives something back.

⚖ SUMMARY TABLE

💡 Quick Recap / Memory Tricks

🧠 “S-R-B” Rule:
Selection → Decide
Repetition → Repeat
Branching → Break / Jump

✨ Mnemonic: