Java Void Method Examples: AP Computer Science Code Samples

📚 Quick Study Guide

• 📝 Definition: A `void` method in Java is a method that performs a task but does not return any value to the calling method.
• 🔑 Keyword: The `void` keyword is used in the method signature to indicate that no value will be returned. For example: `public static void printMessage()`.
• 🎯 Purpose: `void` methods are typically used to execute a sequence of statements, perform actions, or produce side effects (e.g., printing output to the console, modifying the state of an object, or drawing graphics).
• 🛑 `return;` Statement: A `return;` statement can be used inside a `void` method to exit the method early, but it cannot be followed by a value.
• 🚫 No Return Value: You cannot assign the result of a `void` method call to a variable because it doesn't return anything. For instance, `int x = printMessage();` would cause a compilation error.
• ⚙️ Parameters: `void` methods can accept any number of parameters, just like methods with return types, to perform their tasks based on input.
• 💡 Common Use Cases: Displaying information, updating object attributes, handling events, or any operation where the primary goal is an action rather than producing a specific computed value.

🧠 Practice Quiz

1. ❓ What does the `void` keyword signify in a Java method signature?
   • A) The method returns a boolean value.
   • B) The method does not take any parameters.
   • C) The method does not return any value.
   • D) The method can only be called from within the same class.
2. ❓ Which of the following is a valid method signature for a `void` method named `calculateAndPrint` that takes an `int` and a `double` as parameters?
   • A) `public int calculateAndPrint(int a, double b)`
   • B) `public void calculateAndPrint(int a, double b)`
   • C) `public calculateAndPrint(int a, double b) void`
   • D) `public void calculateAndPrint(int a, double b) returns nothing`
3. ❓ Consider the following Java code snippet:

   public class MyClass {
       public static void greet(String name) {
           System.out.println("Hello, " + name + "!");
       }
   
       public static void main(String[] args) {
           // Line X
       }
   }

   Which of the following lines would correctly call the `greet` method in `Line X`?
   • A) `String message = greet("Alice");`
   • B) `greet("Alice");`
   • C) `void result = greet("Alice");`
   • D) `System.out.println(greet("Alice"));`
4. ❓ What happens if you include `return "Hello";` inside a `void` method?
   • A) The method will return the string "Hello".
   • B) It will cause a compile-time error.
   • C) The method will print "Hello" and then exit.
   • D) The program will run but ignore the `return` statement.
5. ❓ Which of these is a typical use case for a `void` method?
   • A) Calculating the square root of a number.
   • B) Returning the sum of two integers.
   • C) Printing a menu to the console.
   • D) Determining if a number is prime.
6. ❓ If a `void` method contains the statement `return;`, what is its effect?
   • A) It causes a compile-time error.
   • B) It returns a `null` value.
   • C) It immediately terminates the method execution.
   • D) It indicates that the method should return a value later.
7. ❓ Which statement about `void` methods is TRUE?
   • A) A `void` method must always be `static`.
   • B) A `void` method cannot have parameters.
   • C) A `void` method can modify the state of an object.
   • D) A `void` method can be used on the right-hand side of an assignment operator.