1Z0-819 Java Fundamentals & Object-Oriented Programming

Question 1

What is the main purpose of the Java Virtual Machine (JVM)?

Accepted Answer

To convert Java bytecode to machine code at runtime

Answer

The Java Virtual Machine (JVM) is responsible for executing Java bytecode. After Java source code is compiled into bytecode, the JVM translates this platform-independent bytecode into machine-specific instructions at runtime. This 'write once, run anywhere' capability is a core feature of Java, enabled by the JVM's role as an interpreter and runtime environment.

Question 2

Which keyword is used to create a subclass in Java?

Accepted Answer

extends

Answer

In Java, the `extends` keyword is used to establish an inheritance relationship between classes. When a class `A` `extends` class `B`, `A` becomes a subclass (or child class) of `B`, inheriting its public and protected methods and fields. This promotes code reuse and establishes an 'is-a' relationship.

Question 3

What is encapsulation in object-oriented programming?

Accepted Answer

Using private fields with public getters/setters

Answer

Encapsulation is an object-oriented programming principle that bundles data (fields) and methods that operate on the data within a single unit (a class). It involves restricting direct access to some of an object's components, typically by making fields `private`. Access to these private fields is then controlled through public `getter` and `setter` methods, ensuring data integrity and controlled modification.

Question 4

What does the 'static' keyword denote in Java?

Accepted Answer

Class-level access without needing an object

Answer

The `static` keyword in Java indicates that a member (field or method) belongs to the class itself, rather than to any specific instance of the class. This means you can access `static` members directly using the class name, without needing to create an object of that class. `static` methods can only access `static` variables and call `static` methods.

Question 5

Which of the following is not a Java access modifier?

Accepted Answer

Answer

Java has four primary access modifiers: `public`, `protected`, `private`, and the default (package-private, which has no keyword). The term 'friendly' is sometimes informally used to describe the default access level, but it is not a reserved keyword or a formal access modifier in Java. Therefore, `friendly` is not a Java access modifier.

(1Z0-819) Oracle Java SE 11 Developer Practice Test

(1Z0-819) Oracle Java SE 11 Developer Practice Test

1Z0-819 Java Fundamentals & Object-Oriented Programming