Method declaration in Java - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a method named greet that returns nothing.

Java

public [1] greet() {
    System.out.println("Hello!");
}

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

Avoid

BString

Cint

Dclass

Attempts:

3 left

💡 Hint

Common Mistakes

Using a return type like int or String when the method does not return anything.

Using 'class' instead of a return type.

The keyword 'void' is used to declare a method that does not return any value.

2fill in blank

medium

Complete the code to declare a method named add that returns an integer.

Java

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

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

Avoid

BString

Cdouble

Dint

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'void' when the method returns a value.

Using 'String' or 'double' as return type incorrectly.

The method returns the sum of two integers, so the return type must be 'int'.

3fill in blank

hard

Fix the error in the method declaration to make it valid.

Java

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

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

Avoid

BcalculateSum

Cint

Dsum

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'void' as return type when the method returns a value.

Using the method name as return type.

The method returns an integer sum, so the return type must be 'int'. Using 'void' causes a compile error because the method returns a value.

4fill in blank

hard

Fill both blanks to declare a method named multiply that returns the product of two doubles.

Java

public [1] multiply([2] a, [2] b) {
    return a * b;
}

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

Adouble

Bint

Cfloat

DString

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'int' or 'float' instead of 'double'.

Using different types for return and parameters.

The method returns a double and takes two double parameters, so both blanks must be 'double'.

5fill in blank

hard

Fill all three blanks to declare a method named isEven that returns true if a number is even.

Java

public [1] isEven([2] num) {
    return num [3] 2 == 0;
}

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

Aboolean

Bint

C%

Ddouble

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'void' or 'int' as return type instead of 'boolean'.

Using '/' instead of '%' for modulus.

Using 'double' instead of 'int' for the parameter.

The method returns a boolean, takes an int parameter, and uses the modulus operator '%' to check if num is divisible by 2.

Practice

1. What is the correct way to declare a method in Java that returns an integer and takes no parameters?

easy

A. int getNumber { return 5; }

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

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

D. public int getNumber[] { return 5; }

Solution

1. Step 1: Check method signature format

   The correct method declaration includes access modifier, return type, method name, and parentheses for parameters.

2. Step 2: Validate syntax correctness

   public int getNumber() { return 5; } correctly uses 'public int getNumber()' with parentheses and a return statement.

3. Final Answer:

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

4. Quick Check:

   Method declaration = public int getNumber() { ... } [OK]

Hint: Method declaration needs return type, name, and parentheses [OK]

Common Mistakes:

• Omitting parentheses after method name
• Missing return type before method name
• Using brackets [] instead of parentheses for parameters

2. Which of the following is a correct method declaration syntax in Java?

easy

A. void printMessage(String message) { System.out.println(message); }

B. void printMessage(String message); { System.out.println(message); }

C. void printMessage String message { System.out.println(message); }

D. void printMessage(String message) System.out.println(message);

Solution

1. Step 1: Identify correct method header and body syntax

   Method header must have parentheses around parameters and body enclosed in braces.

2. Step 2: Check for syntax errors

   void printMessage(String message) { System.out.println(message); } correctly declares method with parameters in parentheses and body in braces.

3. Final Answer:

   void printMessage(String message) { System.out.println(message); } -> Option A

4. Quick Check:

   Method syntax = returnType name(params) { body } [OK]

Hint: Method parameters must be inside parentheses and body inside braces [OK]

Common Mistakes:

• Adding semicolon after method header
• Missing parentheses around parameters
• Omitting braces for method body

3. What will be 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. 0

B. 34

C. 7

D. Error

Solution

1. Step 1: Understand method call and parameters

   The method add takes two integers and returns their sum.

2. Step 2: Calculate the return value

   Calling add(3, 4) returns 3 + 4 = 7, which is printed.

3. Final Answer:

   7 -> Option C

4. Quick Check:

   3 + 4 = 7 [OK]

Hint: Method add returns sum; 3 + 4 = 7 [OK]

Common Mistakes:

• Confusing concatenation with addition
• Expecting compile error due to static method
• Ignoring return value and expecting no output

4. Identify the error in the following method declaration:

public int multiply(int x, int y)
  return x * y;
}

medium

A. Extra semicolon after return statement

B. Missing return type

C. Incorrect parameter types

D. Missing opening brace '{' after method header

Solution

1. Step 1: Check method header and body braces

   The method header must be followed by an opening brace '{' to start the method body.

2. Step 2: Identify missing brace

   The code lacks '{' after the method header, causing a syntax error.

3. Final Answer:

   Missing opening brace '{' after method header -> Option D

4. Quick Check:

   Method body must start with '{' [OK]

Hint: Method body always starts with '{' after header [OK]

Common Mistakes:

• Forgetting opening brace '{'
• Placing return statement outside method body
• Confusing semicolon placement

5. You want to declare a method named filterPositive that takes an array of integers and returns a new array containing only the positive numbers. Which method declaration is correct?

hard

A. public int[] filterPositive(int[] numbers) { /* implementation */ }

B. public int filterPositive(int numbers[]) { /* implementation */ }

C. public void filterPositive(int[] numbers) { /* implementation */ }

D. public int filterPositive(int[] numbers[]) { /* implementation */ }

Solution

1. Step 1: Determine return type and parameter type

   The method returns an array of integers, so return type must be int[]. The parameter is an int array.

2. Step 2: Check syntax correctness

   public int[] filterPositive(int[] numbers) { /* implementation */ } correctly declares return type as int[] and parameter as int[]. Other options have wrong return types or parameter syntax.

3. Final Answer:

   public int[] filterPositive(int[] numbers) { /* implementation */ } -> Option A

4. Quick Check:

   Return type matches output array type [OK]

Hint: Return type must match method output type (int[] for array) [OK]

Common Mistakes:

• Using int instead of int[] as return type
• Incorrect parameter array syntax
• Using void when method returns data