Java Programming Fundamentals

File.createNewFile() creates the file ONLY if it does not already exist. If the file exists (like test.txt in this case), the method returns false and does nothing - it does NOT overwrite. This method only throws IOException if there's a directory issue or permission problem, not if the file exists. Option A is wrong because existing files are not overwritten.

In Java, enums can be used in switch statements, making the first option incorrect. Java enums also implicitly extend java.lang.Enum (not java.lang.Object directly, though Enum inherits Object) and cannot be extended or extend other classes. Thus, options 1 and 4 are incorrect and correctly marked.

The volatile keyword tells the JVM that a variable may be modified by multiple threads asynchronously. This prevents threads from caching the variable's value in CPU registers, ensuring all reads and writes go directly to main memory where all threads can see the latest value.

A Set in Java automatically removes duplicates because it only stores unique elements. By adding all elements from a List to a Set (like HashSet), duplicates are automatically eliminated. You can then convert back to a List if needed.

Abstract classes cannot be instantiated directly because they are designed to be incomplete. You must create a concrete subclass that implements all abstract methods before you can create objects. Only concrete subclasses can be instantiated using the new keyword.

Constructors are not inherited in Java - each class must define its own constructors. A subclass can call a superclass constructor using super(), but this is explicit invocation, not inheritance. If you don't write any constructor, Java provides a default no-arg constructor that calls super().

In Java, java.lang.Object is the root of the class hierarchy. Every Java class implicitly or explicitly extends Object, making it the ultimate superclass. 'public void class' is invalid syntax, and inner/outer classes are nesting patterns.

Java DOES support pass-by-reference in a limited sense - object references are passed by value. When you pass an object reference, you can modify the object's contents but cannot make the reference point to a different object. The claim that Java 'does not support pass by reference only pass by value' is therefore false - it's more nuanced.

The java.lang.String class is explicitly declared with the final modifier in the Java API. This design prevents other classes from subclassing it, ensuring security, optimization, and immutability of string objects.

Java only supports variables defined within a class or method scope. Variables defined at the class level with static act similarly to global variables but are still scoped within their class, meaning Java does not have true global variables.

The main() method must be declared static so the JVM can call it without instantiating the class. This is a fundamental Java requirement - the JVM needs an entry point it can invoke using the class name directly, without needing to create an object first.

The Java java.lang.Object class contains methods like wait(), toString(), notify(), notifyAll(), and finalize(). Methods like run() and stop() belong to the Thread or Runnable interfaces, not the Object class.