If statement in Java - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of an if statement in Java?

An if statement lets the program decide to run some code only if a condition is true. It helps the program make choices.

beginner

Write the basic syntax of an if statement in Java.

The basic syntax is:

if (condition) {
  // code to run if condition is true
}

beginner

What happens if the condition in an if statement is false?

If the condition is false, the code inside the if block does not run. The program skips it and continues.

beginner

Can an if statement be used without an else part?

Yes, an if statement can stand alone. The else part is optional and runs code when the condition is false.

beginner

How do you write an if-else statement in Java?

You write it like this:

if (condition) {
  // code if true
} else {
  // code if false
}

What does the if statement check in Java?

A A condition that is true or false

B A loop counter

C A variable declaration

D A method call

The if statement checks a condition that evaluates to true or false to decide which code to run.

What happens if the if condition is false and there is no else?

A The program skips the <code>if</code> block and continues

B The program runs the code inside the <code>if</code> block

C The program stops running

D The program throws an error

If the condition is false and no else is present, the program skips the if block and continues.

Which of these is the correct syntax for an if statement?

A if condition { }

B if condition then { }

C if [condition] { }

D if (condition) { }

In Java, the condition must be inside parentheses: if (condition) { }.

Can you have multiple if statements one after another?

A No, only one <code>if</code> per program

B Only if they have <code>else</code> parts

C Yes, you can have many <code>if</code> statements

D Only if they are inside a loop

You can have many if statements in a program to check different conditions.

What keyword do you use to run code when an if condition is false?

A elseif

B else

C when

D otherwise

The keyword else runs code when the if condition is false.

Explain how an if statement works in Java and write a simple example.

Think about how you decide to do something only if a certain condition is true.

Describe the difference between an if statement and an if-else statement.

Consider what happens when the condition is false.

Practice

1. What does an if statement do in Java?

easy

A. It stores data in a variable.

B. It repeats code multiple times.

C. It creates a new class.

D. It runs code only if a condition is true.

Solution

1. Step 1: Understand the purpose of an if statement

   An if statement checks a condition and decides whether to run some code based on that condition.

2. Step 2: Match the description to the options

   It runs code only if a condition is true. correctly says it runs code only if the condition is true, which matches the if statement's behavior.

3. Final Answer:

   It runs code only if a condition is true. -> Option D

4. Quick Check:

   If statement = runs code if true [OK]

Hint: If checks true condition to run code [OK]

Common Mistakes:

• Confusing if with loops
• Thinking if stores data
• Mixing if with class creation

2. Which of these is the correct syntax for an if statement in Java?

easy

A. if (condition) System.out.println("Yes");

B. if condition { System.out.println("Yes"); }

C. if condition: System.out.println("Yes");

D. if (condition) then { System.out.println("Yes"); }

Solution

1. Step 1: Recall Java if statement syntax

   Java requires parentheses around the condition and braces are optional if only one statement follows.

2. Step 2: Check each option

   if (condition) System.out.println("Yes"); uses parentheses and a single statement without braces, which is valid syntax.

3. Final Answer:

   if (condition) System.out.println("Yes"); -> Option A

4. Quick Check:

   Parentheses needed around condition [OK]

Hint: Use parentheses around condition in if [OK]

Common Mistakes:

• Omitting parentheses around condition
• Using colons instead of braces
• Adding 'then' keyword

3. What will be the output of this code?

int x = 10;
if (x > 5) {
  System.out.println("Big number");
} else {
  System.out.println("Small number");
}

medium

A. Small number

B. Big number

C. No output

D. Syntax error

Solution

1. Step 1: Evaluate the condition x > 5

   Since x is 10, the condition 10 > 5 is true.

2. Step 2: Determine which block runs

   The if block runs and prints "Big number" because the condition is true.

3. Final Answer:

   Big number -> Option B

4. Quick Check:

   10 > 5 is true, prints "Big number" [OK]

Hint: Check if condition true to pick output [OK]

Common Mistakes:

• Choosing else output when condition is true
• Thinking no output if condition true
• Confusing syntax with output

4. Find the error in this code:

int num = 7;
if num > 5 {
  System.out.println("Greater");
}

medium

A. Braces not allowed in if

B. Missing semicolon after if

C. Missing parentheses around condition

D. Wrong variable name

Solution

1. Step 1: Check if statement syntax

   Java requires parentheses around the condition in an if statement.

2. Step 2: Identify the missing parentheses

   The code has if num > 5 without parentheses, which causes a syntax error.

3. Final Answer:

   Missing parentheses around condition -> Option C

4. Quick Check:

   If condition must be in parentheses [OK]

Hint: Always put condition in parentheses [OK]

Common Mistakes:

• Forgetting parentheses around condition
• Adding semicolon after if line
• Misnaming variables

5. You want to print "Even" if a number is even and "Odd" if it is odd. Which code correctly uses an if statement to do this?

int n = 4;
// Your code here

hard

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

B. if (n / 2 == 0) {
System.out.println("Even");
} else {
System.out.println("Odd");
}

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

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

Solution

1. Step 1: Understand how to check even numbers

   A number is even if dividing by 2 leaves remainder 0, so use n % 2 == 0.

2. Step 2: Check each option's condition

   if (n % 2 == 0) { System.out.println("Even"); } else { System.out.println("Odd"); } correctly uses n % 2 == 0 to check evenness and prints "Even" or "Odd" accordingly.

3. Final Answer:

   if (n % 2 == 0) { System.out.println("Even"); } else { System.out.println("Odd"); } -> Option A

4. Quick Check:

   Use modulus == 0 for even check [OK]

Hint: Use n % 2 == 0 to check even numbers [OK]

Common Mistakes:

• Using assignment = instead of comparison ==
• Checking division instead of remainder
• Reversing even and odd conditions