Return values in Java - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to return the sum of two numbers.

Java

public int add(int a, int b) {
    return a [1] b;
}

Drag options to blanks, or click blank then click option'

A+

B-

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction or multiplication instead of addition.

Forgetting to use the return keyword.

The return statement must return the sum of a and b. The plus sign + adds two numbers.

2fill in blank

medium

Complete the method to return the length of the input string.

Java

public int getLength(String text) {
    return text.[1]();
}

Drag options to blanks, or click blank then click option'

Asize

BlengthOf

Clength

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using size() which is for collections, not strings.

Using incorrect method names like count().

The method length() returns the number of characters in a string in Java.

3fill in blank

hard

Fix the error in the method to correctly return the maximum of two numbers.

Java

public int max(int x, int y) {
    if (x > y) {
        return [1];
    } else {
        return y;
    }
}

Drag options to blanks, or click blank then click option'

Ay

B0

Cx + y

Dx

Attempts:

3 left

💡 Hint

Common Mistakes

Returning the wrong variable in the if block.

Returning a sum or zero instead of the correct value.

If x is greater than y, the method should return x. Returning y here would be incorrect.

4fill in blank

hard

Fill both blanks to create a method that returns true if a number is even.

Java

public boolean isEven(int num) {
    return num [1] 2 [2] 0;
}

Drag options to blanks, or click blank then click option'

A%

B==

C!=

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using division / instead of modulo %.

Using inequality != instead of equality ==.

The modulo operator % gives the remainder. If num % 2 == 0, the number is even.

5fill in blank

hard

Fill all three blanks to create a method that returns a new string with the first letter capitalized.

Java

public String capitalize(String word) {
    return word.[1](0, 1).[2]() + word.[3](1);
}

Drag options to blanks, or click blank then click option'

Asubstring

BtoUpperCase

DtoLowerCase

Attempts:

3 left

💡 Hint

Common Mistakes

Using toLowerCase() instead of toUpperCase().

Using wrong indices in substring.

The method takes the first letter with substring(0, 1), converts it to uppercase with toUpperCase(), then adds the rest of the word starting from index 1 with substring(1).

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