Method declaration in Java - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a method with parameters

What is the output of the following Java program?

Java

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

A 7

B 12

C 34

D Error: method multiply not found

💡 Hint

Look at what the multiply method returns when given 3 and 4.

The multiply method returns the product of a and b. 3 times 4 is 12, so the output is 12.

❓ Predict Output

intermediate

Return type and output

What will be printed when this Java code runs?

Java

public class Demo {
    public static String greet() {
        return "Hello!";
    }
    public static void main(String[] args) {
        System.out.println(greet());
    }
}

A null

B greet

C Hello!

D Compilation error

💡 Hint

The greet method returns a string. What does it return exactly?

The greet method returns the string "Hello!" which is printed by main.

❓ Predict Output

advanced

Method overloading output

What is the output of this Java program with overloaded methods?

Java

public class Overload {
    public static int add(int a, int b) {
        return a + b;
    }
    public static double add(double a, double b) {
        return a + b;
    }
    public static void main(String[] args) {
        System.out.println(add(2, 3));
        System.out.println(add(2.0, 3.0));
    }
}

A

5.0
5

B

5
5

C Compilation error due to ambiguous method call

D

5
5.0

💡 Hint

Check which add method is called for int and double arguments.

The first call uses int parameters and calls add(int, int), returning 5. The second call uses double parameters and calls add(double, double), returning 5.0.

❓ Predict Output

advanced

Void method and output

What will be printed when this Java program runs?

Java

public class VoidTest {
    public static void printMessage() {
        System.out.println("Hi there!");
    }
    public static void main(String[] args) {
        printMessage();
        System.out.println("Done");
    }
}

A

Hi there!
Done

B

Done
Hi there!

C Hi there!Done

D Compilation error: void method used in print statement

💡 Hint

Void methods do not return a value but can print inside.

printMessage prints "Hi there!" then main prints "Done" on the next line.

❓ Predict Output

expert

Method recursion output

What is the output of this Java program using recursion?

Java

public class Recursion {
    public static int factorial(int n) {
        if (n <= 1) return 1;
        else return n * factorial(n - 1);
    }
    public static void main(String[] args) {
        System.out.println(factorial(4));
    }
}

A 24

B 10

C Error: StackOverflowError

D 1

💡 Hint

Factorial of 4 is 4 * 3 * 2 * 1.

factorial(4) = 4 * factorial(3) = 4 * 3 * factorial(2) = 4 * 3 * 2 * factorial(1) = 4 * 3 * 2 * 1 = 24.

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