Method parameters in Java - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of method with primitive parameter modification

What is the output of the following Java code?

Java

public class Test {
    public static void modify(int x) {
        x = x + 10;
    }
    public static void main(String[] args) {
        int a = 5;
        modify(a);
        System.out.println(a);
    }
}

A 5

B 15

C Compilation error

D Runtime error

💡 Hint

Think about how Java passes primitive types to methods.

In Java, primitive types are passed by value, so changes inside the method do not affect the original variable.

❓ Predict Output

intermediate

Output of method with object parameter modification

What is the output of this Java program?

Java

class Box {
    int value;
    Box(int v) { value = v; }
}
public class Test {
    public static void modify(Box b) {
        b.value = 10;
    }
    public static void main(String[] args) {
        Box box = new Box(5);
        modify(box);
        System.out.println(box.value);
    }
}

A 10

B Runtime error

C Compilation error

D 5

💡 Hint

Consider how Java passes object references to methods.

Java passes object references by value, so the method can modify the object's fields.

❓ Predict Output

advanced

Output of method with varargs parameter

What will be printed when this Java code runs?

Java

public class Test {
    public static int sum(int... numbers) {
        int total = 0;
        for (int n : numbers) {
            total += n;
        }
        return total;
    }
    public static void main(String[] args) {
        System.out.println(sum(1, 2, 3));
    }
}

A Runtime error

B 123

C Compilation error

D 6

💡 Hint

Varargs allow passing multiple arguments as an array.

The method sums all the integers passed and returns the total.

❓ Predict Output

advanced

Output of method with overloaded parameters

What is the output of this Java program?

Java

public class Test {
    public static void print(int x) {
        System.out.println("int: " + x);
    }
    public static void print(String x) {
        System.out.println("String: " + x);
    }
    public static void main(String[] args) {
        print(5);
        print(null);
    }
}

A Compilation error

B int: 5\nString: null

C int: 5\nRuntime error

D int: 5\nCompilation error

💡 Hint

Consider how Java resolves overloaded methods with null argument.

print(null) unambiguously calls print(String) because null can be assigned to a String reference but not to a primitive int.

❓ Predict Output

expert

Output of method with final parameter and reassignment attempt

What happens when this Java code runs?

Java

public class Test {
    public static void modify(final int x) {
        // x = x + 1; // Uncommenting this line causes what?
        System.out.println(x);
    }
    public static void main(String[] args) {
        modify(5);
    }
}

A Runtime error

B Compilation error due to reassignment of final parameter

C Prints 5

D Prints 6

💡 Hint

Final parameters cannot be reassigned inside the method.

The code as is prints 5. Uncommenting the reassignment line causes a compilation error.

Practice

1. What is the purpose of method parameters in Java?
public void greet(String name) { ... }

easy

A. To declare variables inside the method

B. To define the method's return type

C. To send data into methods so they can use it inside

D. To specify the method's access level

Solution

1. Step 1: Understand method parameters

   Method parameters are variables listed in the method definition that accept values when the method is called.

2. Step 2: Identify their purpose

   They allow sending data into the method so it can perform actions using that data.

3. Final Answer:

   To send data into methods so they can use it inside -> Option C

4. Quick Check:

   Parameters pass data into methods [OK]

Hint: Parameters pass info into methods for flexible use [OK]

Common Mistakes:

• Confusing parameters with return types
• Thinking parameters declare variables inside method body
• Mixing parameters with access modifiers

2. Which of the following is the correct syntax to declare a method with two parameters in Java?

easy

A. public void add(int a; int b) { }

B. public void add(int a, int b) { }

C. public void add(int a int b) { }

D. public void add(int a & int b) { }

Solution

1. Step 1: Recall parameter syntax

   Parameters are listed inside parentheses separated by commas, each with a type and name.

2. Step 2: Check each option

   public void add(int a, int b) { } uses commas correctly; others use semicolon, missing comma, or invalid symbol.

3. Final Answer:

   public void add(int a, int b) { } -> Option B

4. Quick Check:

   Parameters separated by commas [OK]

Hint: Parameters must be comma-separated with type and name [OK]

Common Mistakes:

• Using semicolons instead of commas
• Omitting commas between parameters
• Using invalid symbols like &

3. What will be the output of this Java code?

public class Test {
  public static void printSum(int x, int y) {
    System.out.println(x + y);
  }
  public static void main(String[] args) {
    printSum(5, 3);
  }
}

medium

A. 8

B. 53

C. x + y

D. Compile error

Solution

1. Step 1: Understand method call with parameters

   The method printSum is called with 5 and 3 as arguments, assigned to x and y.

2. Step 2: Calculate the sum inside the method

   Inside printSum, it prints x + y which is 5 + 3 = 8.

3. Final Answer:

   8 -> Option A

4. Quick Check:

   5 + 3 = 8 [OK]

Hint: Sum parameters values to get output [OK]

Common Mistakes:

• Concatenating numbers as strings
• Expecting variable names printed
• Thinking code won't compile

4. Identify the error in this method declaration:

public void displayMessage(String message, int) {
  System.out.println(message);
}

medium

A. Parameter list missing variable name for int type

B. Method must return a value

C. Cannot use String as parameter type

D. System.out.println is invalid here

Solution

1. Step 1: Check parameter list syntax

   Each parameter must have a type and a variable name. Here, int has no name.

2. Step 2: Identify the error

   Missing variable name after int causes a syntax error.

3. Final Answer:

   Parameter list missing variable name for int type -> Option A

4. Quick Check:

   Parameters need type and name [OK]

Hint: Every parameter needs a name after its type [OK]

Common Mistakes:

• Omitting parameter names
• Thinking return type is missing
• Misunderstanding print statement usage

5. You want to create a method that calculates the area of a rectangle. Which method signature correctly uses parameters to accept the rectangle's width and height as doubles?

hard

A. public void area(double width; double height)

B. public double area(width, height)

C. public double area(int width, int height)

D. public double area(double width, double height)

Solution

1. Step 1: Identify correct parameter types and syntax

   The method should accept two double parameters named width and height, separated by commas.

2. Step 2: Evaluate each option

   public double area(double width, double height) correctly declares two double parameters with names and commas; public double area(width, height) misses types; public double area(int width, int height) uses int instead of double; public void area(double width; double height) uses semicolon instead of comma and void return type.

3. Final Answer:

   public double area(double width, double height) -> Option D

4. Quick Check:

   Parameters need type, name, comma-separated [OK]

Hint: Use type and name with commas for parameters [OK]

Common Mistakes:

• Omitting parameter types
• Using wrong separators like semicolons
• Using wrong data types for precision