Return values in Java - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a return value in Java?

A return value is the result a method sends back to the part of the program that called it. It lets the method give information after it finishes running.

beginner

How do you specify the type of value a method returns in Java?

You write the type before the method name in its declaration. For example, int means the method returns an integer number.

intermediate

What happens if a method has a return type other than void but does not use a return statement?

The program will not compile. Java requires that all paths in such a method return a value matching the declared type.

intermediate

Can a method return multiple values directly in Java?

No, a method can return only one value. To return multiple values, you can use an object or an array to hold them.

beginner

What does the void keyword mean in a method declaration?

It means the method does not return any value. It just runs its code and finishes without sending anything back.

What keyword is used to send a value back from a method in Java?

A output

B send

C return

D yield

The return keyword is used to send a value back from a method.

If a method is declared as int calculate(), what must it do?

A Return an integer value

B Return nothing

C Return a string

D Throw an exception

The method must return an integer value because its return type is int.

What will happen if a method with return type double does not have a return statement?

A Runs without error

B Compilation error

C Returns null

D Returns 0.0 automatically

Java requires a return statement for methods with a non-void return type, otherwise it causes a compilation error.

Which of these methods does NOT return a value?

A void printMessage()

B int getNumber()

C String getName()

D double calculateArea()

Methods declared with void do not return any value.

How can a method return multiple values in Java?

A By calling return several times

B By using multiple return statements

C By declaring multiple return types

D By returning an object or array containing the values

Java methods can return only one value, but that value can be an object or array holding multiple pieces of data.

Explain what a return value is and why it is useful in Java methods.

Think about how methods communicate results to the rest of the program.

Describe the difference between a method with a void return type and one with a specific return type.

Consider what happens after the method finishes running.

Practice

1. What does the return keyword do in a Java method?

easy

A. It stops the program completely.

B. It sends a value back from the method to where it was called.

C. It prints a value to the screen.

D. It declares a new variable inside the method.

Solution

1. Step 1: Understand the purpose of return

   The return keyword is used inside a method to send a value back to the caller.

2. Step 2: Differentiate from other actions

   Stopping the program, printing, or declaring variables are different actions and not what return does.

3. Final Answer:

   It sends a value back from the method to where it was called. -> Option B

4. Quick Check:

   Return sends value back [OK]

Hint: Return sends data back from method to caller [OK]

Common Mistakes:

• Thinking return stops the whole program
• Confusing return with print statements
• Assuming return declares variables

2. Which of the following method signatures correctly declares a method that returns an integer?

easy

A. public String getNumber() { return 5; }

B. public void getNumber() { return 5; }

C. public int getNumber() { return 5; }

D. public int getNumber() { System.out.println(5); }

Solution

1. Step 1: Check method return type and return statement

   The method must declare int as return type to return an integer value.

2. Step 2: Match return type with returned value

   public int getNumber() { return 5; } declares int and returns 5, which is an integer, so it is correct.

3. Final Answer:

   public int getNumber() { return 5; } -> Option C

4. Quick Check:

   Return type matches returned value [OK]

Hint: Return type must match returned value type [OK]

Common Mistakes:

• Using void but returning a value
• Returning wrong type value
• Missing return statement in non-void method

3. What is the output of the following code?

public class Test {
  public static int add(int a, int b) {
    return a + b;
  }
  public static void main(String[] args) {
    System.out.println(add(3, 4));
  }
}

medium

A. 7

B. 34

C. Error

D. 0

Solution

1. Step 1: Understand the add method

   The method adds two integers and returns their sum.

2. Step 2: Calculate add(3, 4)

   3 + 4 equals 7, so the method returns 7.

3. Final Answer:

   7 -> Option A

4. Quick Check:

   3 + 4 = 7 [OK]

Hint: Add numbers, return sum, print result [OK]

Common Mistakes:

• Concatenating numbers as strings
• Expecting error due to return
• Confusing return with print

4. Identify the error in this method:

public int multiply(int x, int y) {
  int result = x * y;
}

medium

A. Method name is invalid.

B. Method return type should be void.

C. Variables x and y are not declared.

D. Method is missing a return statement.

Solution

1. Step 1: Check method return type

   The method declares it returns an int, so it must return an int value.

2. Step 2: Verify return statement presence

   The method calculates result but does not return it, so it misses a return statement.

3. Final Answer:

   Method is missing a return statement. -> Option D

4. Quick Check:

   Non-void methods must return a value [OK]

Hint: Non-void methods must have return statement [OK]

Common Mistakes:

• Forgetting to return value in non-void method
• Changing return type to void without reason
• Assuming variable declaration is error

5. Given this method:

public static String checkNumber(int n) {
  if (n > 0) return "Positive";
  else if (n < 0) return "Negative";
  else return "Zero";
}

What will checkNumber(0) return?

hard

A. "Zero"

B. "Negative"

C. "Positive"

D. null

Solution

1. Step 1: Analyze the if-else conditions

   If n > 0 returns "Positive", if n < 0 returns "Negative".

2. Step 2: Check the else case for n = 0

   Since 0 is neither greater nor less than 0, else returns "Zero".

3. Final Answer:

   "Zero" -> Option A

4. Quick Check:

   0 triggers else return "Zero" [OK]

Hint: Check all conditions including else for exact return [OK]

Common Mistakes:

• Assuming 0 is positive or negative
• Missing else return case
• Expecting null when no return