Creating Decision-Making Statements

Decision-making statements control which code paths execute at runtime. Java provides if, if/else, and if/else if/else chains as the foundational building blocks for branching logic.

The if Statement

An if statement executes a block only when its boolean expression evaluates to true:

java
int score = 85;

if (score >= 60) {
    System.out.println("Passed");
}

The condition must be a boolean or Boolean expression — unlike C or C++, an integer is not valid:

java
int x = 1;
if (x) { }   // compile-time error: incompatible types

The if/else Statement

An else clause runs when the condition is false:

java
int temperature = 18;

if (temperature >= 20) {
    System.out.println("Warm day");
} else {
    System.out.println("Cool day");
}

Exactly one branch executes — never both, never neither.

The if/else if/else Chain

Multiple conditions can be chained together. Java evaluates them top-to-bottom and executes the first branch whose condition is true:

java
int score = 72;

if (score >= 90) {
    System.out.println("A");
} else if (score >= 80) {
    System.out.println("B");
} else if (score >= 70) {
    System.out.println("C");
} else {
    System.out.println("F");
}
// Output: C

The trailing else is optional but acts as a catch-all for values that match no preceding condition.

Nested if Statements

An if can appear inside another if or else block:

java
boolean isLoggedIn = true;
boolean isAdmin = false;

if (isLoggedIn) {
    if (isAdmin) {
        System.out.println("Admin dashboard");
    } else {
        System.out.println("User dashboard");
    }
} else {
    System.out.println("Login required");
}

Deep nesting quickly becomes hard to read. Prefer early returns or pattern matching where appropriate.

Comparison: Statement Forms

Common Pitfall: Missing Braces

Without braces, only the single next statement belongs to the if or else:

java
int x = 5;

if (x > 3)
    System.out.println("Greater");   // inside the if
    System.out.println("Always");    // ALWAYS runs — NOT part of the if

This compiles without error but is a frequent source of bugs. The OCP exam tests this directly.

The Dangling else Problem

When braces are omitted, an else binds to the nearest preceding if:

java
int x = 10;
int y = 5;

if (x > 5)
    if (y > 10)
        System.out.println("Both");
else
    System.out.println("Else");   // belongs to: if (y > 10), NOT if (x > 5)

Adding braces makes the intent explicit and eliminates ambiguity:

java
if (x > 5) {
    if (y > 10) {
        System.out.println("Both");
    }
} else {
    System.out.println("Else");   // now clearly belongs to if (x > 5)
}

Best practice: always use braces, even for single-statement bodies.

Common Pitfall: Assignment Inside Condition

A classic typo replaces == with =, which produces a compile-time error in Java for primitive boolean contexts:

java
boolean active = false;

if (active = true) {   // assigns true, then evaluates as true — compiles!
    System.out.println("This always runs");
}

Java does allow assignment inside a boolean condition (unlike C, it produces a boolean result only when the assigned type is boolean). The compiler will warn but not always reject it. Use == for comparisons.

Ternary Operator as a Compact Alternative

For simple value selection, the ternary operator ? : replaces an if/else:

java
int age = 20;
String status = (age >= 18) ? "adult" : "minor";
System.out.println(status);  // adult

The ternary is an expression (it produces a value), not a statement. Do not use it for complex logic — keep it for concise value assignments.

Key Rules to Remember

• The condition of an if must be a boolean expression
• Only the first matching branch in an if/else if chain executes
• An else binds to the nearest unmatched if when braces are omitted
• Single-statement bodies without braces are legal but error-prone
• null assigned to a Boolean parameter and unboxed causes NullPointerException

References

• Oracle Docs — The if-then and if-then-else Statements (Java 21)
• Java Language Specification — §14.9 The if Statement