Java if Statements

Learn to make your programs decide: execute code only when a Boolean condition is true, branch with else, and chain logic with else if.

AP Computer Science A

What Is an if Statement?

An if statement is the most fundamental control structure in Java. It lets your program make decisions by testing a Boolean condition and executing a block of code only when that condition evaluates to true.

Boolean Conditions: The Gateway

Every if statement relies on a Boolean expression: an expression that evaluates to either true or false. Java provides several comparison operators to build these expressions:

\(==\)

Equal to

\(!=\)

Not equal to

\(\gt\) \(\lt\)

Greater / Less than

\(\ge\) \(\le\)

Greater/Less or equal

Why if Statements Matter

Without conditional logic, programs can only execute instructions sequentially: line after line, with no ability to adapt. The if statement unlocks three critical capabilities:

1

Input validation: Check whether user data is acceptable before processing it.

2

Branching logic: Choose different actions based on the current state of variables.

3

Error handling: Detect and respond to unexpected situations before they crash the program.

The Syntax of an if Statement

if (condition) {
    // code to execute when condition is true
}

1

Keyword if: tells Java a conditional block follows.

2

Parentheses ( ): contain the Boolean expression to test.

3

Braces { }: wrap the body. If the condition is true, every statement inside runs. If false, the entire block is skipped.

How an if Flows

Adding an else Branch

When you need to do one thing if a condition is true and a different thing if it is false, add an else clause:

if (temperature > 100) {
    System.out.println("Boiling!");
} else {
    System.out.println("Not boiling.");
}

Chaining with else if

When there are more than two possibilities, chain multiple conditions using else if. Java evaluates them top to bottom and executes the first block whose condition is true:

if (score >= 90) {
    grade = "A";
} else if (score >= 80) {
    grade = "B";
} else if (score >= 70) {
    grade = "C";
} else {
    grade = "F";
}

if vs if-else vs else if

if alone

Tests one condition. Body runs or is skipped: 0 or 1 blocks execute.

if-else

Two-way branch. Exactly 1 of 2 blocks always executes.

else if chain

Multi-way branch. Exactly 1 of N blocks executes (if a final else is present).

How to Apply if Statements

1

Identify the decision: What question does the program need to answer?

2

Write the Boolean expression: Translate the question into a comparison using \(==\), \(!=\), \(\lt\), \(\gt\), \(\le\), or \(\ge\).

3

Determine the structure: Do you need just if, if-else, or an else if chain?

4

Write the body: Place the statements to execute inside curly braces { }.

5

Trace with test values: Mentally run through with a true case and a false case to verify correctness.

Example 1: Simple if

int age = 17;

if (age >= 16) {
    System.out.println("You can drive.");
}

System.out.println("Program continues.");

Example 2: if-else in Action

int num = 7;

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

Example 3: else if Chain

int temp = 35;

if (temp >= 90) {
    System.out.println("Hot");
} else if (temp >= 60) {
    System.out.println("Warm");
} else if (temp >= 32) {
    System.out.println("Cold");
} else {
    System.out.println("Freezing");
}

Common Mistakes

✕ Using \(=\) instead of \(==\)

Writing if (x = 5) assigns 5 to x rather than comparing. Java will flag a type error because the result is an int, not a boolean.

✕ Forgetting braces

Without { }, only the very next statement is controlled by the if. The second line always runs, causing logic errors.

✕ Semicolon after if

Writing if (x > 0); creates an empty body. The block below executes unconditionally regardless of the condition.

Summary Comparison

	if	if-else	else if chain
Branches	1	2	N
Blocks executed	0 or 1	Exactly 1	Exactly 1 (with else)
Mutual exclusion	No	Yes	Yes
Requires else?	No	Yes	Optional (recommended)
Use when	One optional action	Two alternatives	Multiple categories

Question 1 of 5

What is printed by the following code?

int x = 10;
if (x > 5) {
    System.out.print("A");
}
if (x > 8) {
    System.out.print("B");
}

These are two separate if statements (not if-else), so each condition is evaluated independently. Since \(10 \gt 5\) is true AND \(10 \gt 8\) is true, both bodies execute, printing AB.

Question 2 of 5

What is printed by the following code?

int x = 10;
if (x > 5) {
    System.out.print("A");
} else if (x > 8) {
    System.out.print("B");
}

This time it is an else if chain. Since the first condition \(10 \gt 5\) is true, "A" prints and the else if is skipped entirely: only the first matching branch executes.

Question 3 of 5

Which of the following will cause a compile-time error in Java?

Java requires the condition inside if parentheses to be a boolean expression. An int value like x is not boolean, so if (x) will not compile. Unlike C/C++, Java does not treat non-zero integers as true.

Question 4 of 5

What does this code print?

int n = 3;
if (n > 0)
    System.out.print("Pos");
    System.out.print("Done");

Without braces, the if controls only the very next statement: "Pos". The second print("Done") is outside the if and always executes. Since \(3 \gt 0\) is true, both print on the same line: PosDone.

Question 5 of 5

What is the value of grade after this code runs with \(score = 85\)?

String grade;
if (score >= 70) {
    grade = "C";
} else if (score >= 80) {
    grade = "B";
} else if (score >= 90) {
    grade = "A";
} else {
    grade = "F";
}

The conditions are checked in wrong order. Since \(85 \ge 70\) is the first true condition, grade is set to "C" and all remaining else-if branches are skipped. This is a classic ordering bug: conditions should go from most restrictive to least restrictive.