Control Flow in Java

Control flow statements determine the order in which your code is executed. By default, Java code runs sequentially (line by line). However, using control flow statements, you can make decisions and run specific blocks of code based on conditions.

1. Conditional Statements (if-else)

Conditional statements allow your program to make decisions based on boolean expressions (conditions that evaluate to either true or false).

The `if` Statement

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

int temperature = 30;

if (temperature > 25) {
    System.out.println("It's a hot day!");
}

The `if-else` Statement

Use else to specify a block of code to run if the condition in the if statement is false.

int age = 16;

if (age >= 18) {
    System.out.println("You are eligible to vote.");
} else {
    System.out.println("You are not eligible to vote yet.");
}

The `if-else-if` Ladder

Use else if to specify a new condition to test if the first condition is false. You can chain multiple else if blocks together.

int marks = 85;

if (marks >= 90) {
    System.out.println("Grade: A+");
} else if (marks >= 80) {
    System.out.println("Grade: A");
} else if (marks >= 70) {
    System.out.println("Grade: B");
} else {
    System.out.println("Grade: C/Pass");
}

Nested `if` Statements

You can place an if statement inside another if statement to check multiple levels of conditions.

int age = 25;
boolean hasLicense = true;

if (age >= 18) {
    if (hasLicense) {
        System.out.println("You are allowed to drive.");
    } else {
        System.out.println("You need a license to drive.");
    }
} else {
    System.out.println("You are too young to drive.");
}

2. Switch Statement

The switch statement selects one of many code blocks to be executed based on the value of an expression. It is often a cleaner alternative to a long if-else-if ladder when comparing a single variable against multiple constant values.

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"); // Output
        break;
    case 4:
        System.out.println("Thursday");
        break;
    case 5:
        System.out.println("Friday");
        break;
    default:
        System.out.println("Weekend!");
}

[!IMPORTANT] The break Keyword: When Java reaches a break keyword, it breaks out of the switch block. If you omit break, execution will “fall through” to the next case, executing its code regardless of whether the condition matches, until a break or the end of the switch block is reached.

3. Ternary Operator (`? :`)

The ternary operator is a shorthand way of writing an if-else statement. It is called ternary because it takes three operands.

Syntax:

variable = (condition) ? expressionTrue : expressionFalse;

Example:

int age = 20;
String status = (age >= 18) ? "Adult" : "Minor";
System.out.println(status); // Outputs: Adult

Best Practices & Common Pitfalls

1. Comparing Strings in Java

Never compare Strings using ==. The == operator compares memory references (addresses), not the actual content of the strings. Always use the .equals() method.

String str1 = new String("Hello");
String str2 = new String("Hello");

// ❌ WRONG (returns false because they are different objects in memory)
if (str1 == str2) { ... }

//  CORRECT (returns true because the content is identical)
if (str1.equals(str2)) { ... }

2. Missing `break` in Switch Cases

Always double-check that every case in a switch block has a break statement unless you are intentionally implementing fall-through behavior.

3. Keep Conditions Readable

Avoid writing overly complex conditions inside a single if statement. If a condition is too long, extract it into a descriptive boolean variable.

// ❌ Hard to read
if (user.isAgeValid() && user.hasActiveSubscription() && !user.isBlocked() && (user.isAdmin() || user.hasPermission("WRITE"))) { ... }

//  Clean and readable
boolean canWrite = user.isAgeValid() && user.hasActiveSubscription() && !user.isBlocked() && (user.isAdmin() || user.hasPermission("WRITE"));
if (canWrite) { ... }

Next Steps ➡️

Now that you know how to make decisions in Java, the next topic will cover how to repeat tasks using Java Loops (Iteration).

Control Flow in Java

1. Conditional Statements (if-else)

The if Statement

The if-else Statement

The if-else-if Ladder

Nested if Statements