Java Basics

Question 1

Method Overloading

Answer 1

• (if a class has) multiple methods having the same name but different parameters
• it increases the readability and reusability of the program
• there are two ways to overload the method: changing the number of arguments; changing the data type
• a good example is System.out.println() method

Question 2

Constant

Answer 2

• it is a value that can’t be changed after assigning it
• We use static and final modifiers (aka non-access modifiers), to declare any variable as constant
• its identifier name must be in capital letters

Question 3

“final” keyword

Answer 3

• it is a non-access modifier applicable only to a variable, a method, or a class
• when a variable is declared with the final keyword, its value can’t be modified.
• when a method is declared with the final keyword, it can’t be overridden.
• when a class is declared with the final keyword, it can’t be extended (inherited).

Question 4

Modifiers

Answer 4

• are specific keywords that we can use to make changes to the characteristics of a variable, method, or class and limit its scope
• Java has two types of modifiers: access modifiers and non-access modifiers

Question 5

Non-Access Modifiers

Answer 5

• provide information about the characteristics of a class, method, or variable.

Question 6

What are the seven types of Non-Access Modifiers?

Answer 6

• static
• final
• abstract
• synchronized
• volatile
• transient
• native

Question 7

static methods

Answer 7

• when a method is declared with the static keyword, it is known as the static method
• Any static member can be accessed before any objects of its class are created and without reference to any object.
• the most common example of a static method is the main() method

Question 8

What are the restrictions of the static methods?

Answer 8

• they can only directly call other static methods
• they can only directly access static data
• they can’t refer to this or super in any way

Question 9

private keyword

Answer 9

an access modifier used for attributes, methods, and constructors, making them only accessible within the declared class

Question 10

protected keyword

Answer 10

used for attributes, methods, and constructors, making them accessible in the same package and subclasses

Question 11

int vs. Integer

Answer 11

• int is a primitive data type while Integer is a type of class

Question 12

“new” keyword

Answer 12

• it is used to create an instance of the class.
• it instantiates a class by allocating memory for a new object and returning a reference to that memory.
• we can also use the new keyword to create the array object

Question 13

What are the two types of data types Java provides?

Answer 13

• primitive

- reference

Question 14

Examples of reference data types

Answer 14

• Array
• class
• interface
• String
• Enumeration
• Annotations

Question 15

Serializable

Answer 15

In Java, it is a marker (empty) interface and has no fields or methods to implement.

Question 16

Serialization

Answer 16

In Java, it is a process of converting the Java code Object into a Byte Stream, to transfer the Object Code from one JVM to another and recreate it using the process of Deserialization.

Question 17

Why need serialization

Answer 17

• communication
• Persistence
• Deep Copy
• Caching
• Cross JVM Synchroniaztion

Question 18

Instantiation

Answer 18

Creating an object of the class

• to call the constructor of a class that creates an instance (object)
• it occupies the initial memory for the object and returns a reference.
• two ways to create an instance: using the new keyword; using the static factory method

Example:
// defines a reference (variable) that can hold an object
ClassName reference;
// instantiation
reference = new Constructor();