This quick reference covers all major Java controls, conditions, and flow control mechanisms with examples.

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Java Controls, Conditions, and Flow Controls Tutorial

Java provides control statements that allow you to direct the flow of your program. These statements decide the order in which code executes based on conditions or loops.

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1. Conditional Statements

Conditional statements allow you to execute certain blocks of code depending on conditions.

1.1 if Statement

The simplest conditional statement. It executes a block if the condition is true.

int number = 10;

if (number > 0) {
    System.out.println("The number is positive");
}

Notes:

• Condition must evaluate to boolean.
• The block is enclosed in {} (optional if single statement, but best practice to always use {}).

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1.2 if-else Statement

Provides an alternative block when the condition is false.

int number = -5;

if (number > 0) {
    System.out.println("Positive number");
} else {
    System.out.println("Non-positive number");
}

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1.3 if-else-if Ladder

Used when multiple conditions need to be checked sequentially.

int score = 75;

if (score >= 90) {
    System.out.println("Grade A");
} else if (score >= 75) {
    System.out.println("Grade B");
} else if (score >= 50) {
    System.out.println("Grade C");
} else {
    System.out.println("Fail");
}

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1.4 Nested if Statements

An if inside another if. Useful for complex conditions.

int number = 20;

if (number > 0) {
    if (number % 2 == 0) {
        System.out.println("Positive even number");
    } else {
        System.out.println("Positive odd number");
    }
}

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1.5 switch Statement

Used when you have multiple possible values for a variable. It's more readable than many if-else statements.

int day = 3;
String dayName;

switch (day) {
    case 1:
        dayName = "Monday";
        break;
    case 2:
        dayName = "Tuesday";
        break;
    case 3:
        dayName = "Wednesday";
        break;
    default:
        dayName = "Invalid day";
}

System.out.println(dayName);

Notes:

• break prevents fall-through to the next case.
• default handles all other values.

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2. Looping Statements (Flow Control)

Loops allow code to execute repeatedly.

2.1 for Loop

Executes a block of code a fixed number of times.

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

Notes:

• Syntax: for(initialization; condition; update)

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2.2 while Loop

Executes a block while a condition is true.

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

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2.3 do-while Loop

Executes a block at least once, then repeats while a condition is true.

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

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2.4 Enhanced for Loop (for-each)

Iterates over arrays or collections.

int[] numbers = {1, 2, 3, 4, 5};

for (int num : numbers) {
    System.out.println(num);
}

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3. Jump Statements

Jump statements change the flow immediately.

3.1 break

Exits a loop or switch.

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

3.2 continue

Skips the current iteration and continues with the next.

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

3.3 return

Exits from a method immediately.

public void checkNumber(int number) {
    if (number < 0) return; // exit method
    System.out.println("Number is " + number);
}

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4. Conditional (Ternary) Operator

Short-hand for if-else.

int number = 10;
String result = (number % 2 == 0) ? "Even" : "Odd";
System.out.println(result);

Syntax:

condition ? valueIfTrue : valueIfFalse

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5. Best Practices for Flow Control

1. Always use {} for blocks, even if optional.
2. Avoid deep nesting; use methods to simplify logic.
3. Prefer switch for multiple discrete values.
4. Use for-each loops for arrays/collections where index is not needed.
5. Use descriptive variable names for conditions and loop counters.

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6. Combined Example

public class FlowDemo {
    public static void main(String[] args) {
        int[] numbers = {10, -3, 0, 25, 8};

        for (int num : numbers) {
            if (num > 0) {
                System.out.println(num + " is positive");
                if (num % 2 == 0) {
                    System.out.println(num + " is even");
                } else {
                    System.out.println(num + " is odd");
                }
            } else if (num < 0) {
                System.out.println(num + " is negative");
            } else {
                System.out.println("Number is zero");
            }
        }
    }
}

Output:

10 is positive
10 is even
-3 is negative
Number is zero
25 is positive
25 is odd
8 is positive
8 is even