Coding Example: Static Variable Usage in Java (AP Computer Science A)

📚 Quick Study Guide

• 🔑 Static Variable Definition: A variable declared with the `static` keyword belongs to the class itself rather than to any specific instance of the class.
• 📦 Memory Allocation: Static variables are allocated memory only once, when the class is first loaded.
• 🌐 Shared Resource: All instances of the class share the same static variable. Changes made by one instance are visible to all other instances.
• 🎯 Usage: Commonly used for constants, counters, or any data that needs to be shared among all objects of the class.
• ✏️ Access: Accessed using the class name followed by the dot operator (e.g., `ClassName.staticVariable`).
• ⚠️ Initialization: Static variables are initialized when the class is loaded, before any objects of the class are created.
• 🛡️ Scope: The scope of a static variable is determined by the access modifier (e.g., `public`, `private`, `protected`).

🧪 Practice Quiz

1. Which of the following statements is true about static variables in Java?
   1. They are unique to each instance of the class.
   2. They are allocated memory each time an object is created.
   3. They belong to the class itself rather than to any specific instance.
   4. They cannot be accessed from outside the class.
2. When is a static variable initialized?
   1. Each time an object of the class is created.
   2. When the class is first loaded.
   3. Only when the main method is executed.
   4. When it is explicitly initialized by the user.
3. If multiple instances of a class modify a static variable, what is the outcome?
   1. Each instance has its own copy of the variable.
   2. The modification only affects the instance that made the change.
   3. All instances share the same modified value.
   4. An error occurs, and the program terminates.
4. How can you access a public static variable from outside the class?
   1. Using the object of the class.
   2. Using the class name followed by the dot operator.
   3. Using the `this` keyword.
   4. It is not possible to access static variables from outside the class.
5. Which of the following is a common use case for static variables?
   1. Storing object-specific data.
   2. Creating temporary variables within a method.
   3. Implementing counters or shared constants.
   4. Defining local variables within a block of code.
6. What happens if you declare a static variable as `private`?
   1. It becomes accessible to all classes.
   2. It can only be accessed within the class it is declared in.
   3. It can only be accessed by subclasses.
   4. It causes a compilation error.
7. Consider the following code: java class MyClass { static int count = 0; MyClass() { count++; } } public class Main { public static void main(String[] args) { MyClass obj1 = new MyClass(); MyClass obj2 = new MyClass(); System.out.println(MyClass.count); } } What will be the output?
   1. 0
   2. 1
   3. 2
   4. 3