Method calling in Java - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of method call with recursion

What is the output of this Java program when the printNumbers method is called with argument 3?

Java

public class Test {
    public static void printNumbers(int n) {
        if (n == 0) return;
        System.out.print(n + " ");
        printNumbers(n - 1);
    }

    public static void main(String[] args) {
        printNumbers(3);
    }
}

A 3 2 1

B 1 2 3

C 3 2 1 0

D 0 1 2 3

💡 Hint

Think about how the method prints before the recursive call and when it stops.

The method prints the current number before calling itself with n-1. It stops when n is 0, so it prints 3, then 2, then 1, each followed by a space.

❓ Predict Output

intermediate

Output of method call with overloaded methods

What is the output of this Java program?

Java

public class OverloadTest {
    public static void display(int a) {
        System.out.println("int: " + a);
    }

    public static void display(String a) {
        System.out.println("String: " + a);
    }

    public static void main(String[] args) {
        display(5);
        display("hello");
    }
}

A

int: 5
String: hello

B

String: 5
int: hello

C

int: 5
int: hello

D

String: 5
String: hello

💡 Hint

Look at the method signatures and which one matches the argument type.

The method display(int) is called with 5, so it prints "int: 5". The method display(String) is called with "hello", so it prints "String: hello".

🔧 Debug

advanced

Identify the error in method call

What error does this Java code produce when compiled?

Java

public class ErrorTest {
    public static void greet() {
        System.out.println("Hello");
    }

    public static void main(String[] args) {
        greet("World");
    }
}

A Runtime error: NullPointerException

B Compilation error: method greet() in class ErrorTest cannot be applied to given types

C Compilation error: missing return statement

D No error, prints "Hello World"

💡 Hint

Check the method signature and how it is called.

The method greet() takes no arguments, but it is called with one String argument "World". This causes a compilation error.

❓ Predict Output

advanced

Output of method call with static and instance methods

What is the output of this Java program?

Java

public class StaticInstance {
    public static void staticMethod() {
        System.out.println("Static method called");
    }

    public void instanceMethod() {
        System.out.println("Instance method called");
    }

    public static void main(String[] args) {
        StaticInstance.staticMethod();
        StaticInstance obj = new StaticInstance();
        obj.instanceMethod();
    }
}

A

Static method called
Static method called

B

Instance method called
Static method called

C

Static method called
Instance method called

D

Instance method called
Instance method called

💡 Hint

Static methods are called on the class, instance methods on objects.

The static method is called first and prints "Static method called". Then the instance method is called on the object and prints "Instance method called".

❓ Predict Output

expert

Output of method call with method overriding and polymorphism

What is the output of this Java program?

Java

class Parent {
    void show() {
        System.out.println("Parent show");
    }
}

class Child extends Parent {
    @Override
    void show() {
        System.out.println("Child show");
    }
}

public class TestPolymorphism {
    public static void main(String[] args) {
        Parent obj = new Child();
        obj.show();
    }
}

A Runtime error: ClassCastException

B Parent show

C Compilation error: cannot override show()

D Child show

💡 Hint

Look at which method is called when a Parent reference points to a Child object.

The method show() is overridden in Child. Even though the reference is Parent, the actual object is Child, so Child's show() is called.

Practice

1. What does calling a method in Java do?
myMethod();

easy

A. Runs the instructions inside the method named myMethod.

B. Creates a new method called myMethod.

C. Deletes the method myMethod from the program.

D. Prints the name myMethod on the screen.

Solution

1. Step 1: Understand what a method call does

   Calling a method means running the code inside that method.

2. Step 2: Analyze the example myMethod();

   This runs the instructions saved inside the method named myMethod.

3. Final Answer:

   Runs the instructions inside the method named myMethod. -> Option A

4. Quick Check:

   Method call = run method code [OK]

Hint: Method call runs code inside method name() [OK]

Common Mistakes:

• Thinking method call creates or deletes methods
• Confusing method call with printing text
• Assuming method call changes method definition

2. Which of the following is the correct way to call a method named displayMessage in Java?

easy

A. run displayMessage();

B. call displayMessage();

C. displayMessage;

D. displayMessage();

Solution

1. Step 1: Recall Java method call syntax

   In Java, you call a method by writing its name followed by parentheses.

2. Step 2: Check each option

   Only displayMessage(); matches the correct syntax for calling a method.

3. Final Answer:

   displayMessage(); -> Option D

4. Quick Check:

   Method call syntax = name() [OK]

Hint: Method call needs parentheses after name [OK]

Common Mistakes:

• Omitting parentheses when calling methods
• Adding extra words like 'call' or 'run'
• Using semicolon without parentheses

3. What is the output of this Java code?

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

medium

A. sayHi()

B. No output

C. Hi there!

D. Compilation error

Solution

1. Step 1: Identify the method call in main

   The main method calls sayHi(), which prints "Hi there!".

2. Step 2: Understand what sayHi() does

   It prints the text "Hi there!" to the screen.

3. Final Answer:

   Hi there! -> Option C

4. Quick Check:

   Method prints text = output text [OK]

Hint: Method prints text, so output is printed string [OK]

Common Mistakes:

• Confusing method name with output
• Expecting no output without print statement
• Thinking method call causes error

4. Find the error in this Java code snippet:

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

medium

A. Incorrect method name.

B. Missing parentheses when calling method greet.

C. Missing semicolon after greet.

D. Method greet is not defined.

Solution

1. Step 1: Check method call syntax in main

   The code uses greet; which is missing parentheses.

2. Step 2: Understand correct method call

   Method calls require parentheses even if no arguments: greet();.

3. Final Answer:

   Missing parentheses when calling method greet. -> Option B

4. Quick Check:

   Method call needs () [OK]

Hint: Always use () to call methods, even if empty [OK]

Common Mistakes:

• Forgetting parentheses on method calls
• Thinking semicolon alone calls method
• Assuming method call without () is valid

5. Given this Java code:

public class Calculator {
  public static int add(int a, int b) {
    return a + b;
  }
  public static void main(String[] args) {
    int result = add(5, 3);
    System.out.println(result);
  }
}

What will be printed when the program runs?

hard

A. 8

B. 53

C. add(5, 3)

D. Compilation error

Solution

1. Step 1: Understand method add parameters and return

   The method add takes two integers and returns their sum.

2. Step 2: Analyze the call add(5, 3)

   It returns 5 + 3 = 8, which is stored in result.

3. Step 3: Check the output statement

   System.out.println(result); prints the value 8.

4. Final Answer:

   8 -> Option A

5. Quick Check:

   Sum of 5 and 3 = 8 [OK]

Hint: Method returns sum; print shows result [OK]

Common Mistakes:

• Concatenating numbers as strings instead of adding
• Expecting method name printed instead of result
• Confusing return value with method call syntax