Java 1

Question 1

Method Overloading

Answer 1

• Used for reusability and readability
• Same name with different parameters
• In this way you can have the same name of method do different and specific tasks and return different values

Parts of Method:

• Name
• Parameters
• Returns

Question 2

What does continue keyword perform ?

Answer 2

In a loop if you put continue it will start the iterator again from the next index

Question 3

Word.length

Answer 3

length starts at 1 not 0 index.
Lawn has a length of 4
The index does start at 0

Question 4

5/2

Answer 4

2

Question 5

An ArrayList collection ..

Answer 5

Can only store objects and not primitives

Question 6

Name Standards

Answer 6

packages: always lowercase
ClassNames: start with capital and then do camel case
methods: start with lower case and then camelCase
CONSTANTS: ARE ALL CAPS

Question 7

What is Stack Memory and what is stored

Answer 7

• primitive values or the object variables

Ex: Car toyota

Question 8

What is HEAP memory and how is it used ?

Answer 8

• HEAP is larger than STACK
• String Pool is inside HEAP
• Objects are placed into HEAP
  Ex: new Toyota

Question 9

What is String pool ?
Explain what word.toUpperCase does to String value?
Why is a String immutable ?

Answer 9

Special space in HEAP java memory where String objects are places and reused.
- If a string is already exists in String pool java will reuse it. Ex: if “java word” already exists and you do String value = “java word”, the word will not be created in String pool it will simple let value variable name point to “java word”

• To always create a new String Object even if it already exists in the String pool do:
• String word = new String(“New Java Word”)
• it will create a new string object in HEAP outside the String pool

String name = null

• since it is null does not point to any object in Heap String pool
• the name is just sitting in stack

wordNew = word.toUpperCase
- Will go to HEAP and it will point to the uppercase version of the word without changing the word itself. Therefore it is immutable

String word 2 = “hello” + “world”;

• String pool will create hello, world and then hello world
• word2 will point to hello world and the other hello and word will go to garbage collector

Question 10

String builder vs String Buffer

Answer 10

Both allow us to use other methods to manipulate strings
However, they have different implementations
String input = “Java is good”;

StringBuilding word1 = new StringBuilder();
word1.append(input)

StringBuffer word2 = new StringBuffer(input);

Now you can do word1.reverse();

Question 11

Encapsulation Principles?

Answer 11

• Used for data hiding/ information hiding
• Make instance variables Private and provide public getter and setter methods to have access
• Private variables can only be accessed/changed in the same class.

Question 12

Encapsulation Benefits?

Answer 12

• Protects instance variables from invalid values
• We can use java code conditions in setter methods to provide criteria on how a value can be assigned. If criteria is not being met, then value is not assigned.
• Customize getter methods to return data in certain ways
• toString method is a special method that exists in each and every object

Question 13

In Encapsulation what is immutable class ?

What is Write-only class?

Answer 13

• We only provide getters and no setters
  
  • This means that the constructor must have the “this name = name” to store values
    Ex: Person person = new Person(“Johnny”, 25);
    person.getName();
    person.getAge();

Write only object? Provide only setters and no getters

Question 14

Constructors facts:

Answer 14

• Must have for every class, if not provide then java will provide a no arg constructor when the class is executed at run time.
• No return type
• no-arg constructor is known as default constructor
• Constructor is called every time we use the “new” keyword
• If you have various constructor with different args, the constructor that will be used will depend on which parameters are being sent.

Person person1 = new Person("Johnny", 20);
Person person1 = new Person("Johnny");
Person person1 = new Person(20);
Person person1 = new Person();

Question 15

What is composition ?

Answer 15

When a class has instance variables of type of another class
- HAS-A relationship

Bus:
Properties: Driver, Engine
Bus HAS-A Driver
Bus HAS-A Engine

Question 16

Static - method related

Answer 16

• Used to call methods from other classes without having to instantiate class.
• Static methods can only access call of refer to other static variables or other static methods.
• Instance methods can do both, static and non-static variables and methods

Question 17

Static - Variable

Answer 17

• it is a shared variable, only single copy of that variable for the entire class.
• Therefore, many other object of that class can change the values of this static keyword and it affect the other classes as well.

Question 18

Static Block

Answer 18

• Code of block that runs BEFORE anything else when a class is loaded to memory.
• Runs BEFORE constructor
• Can be used to initialize and assign data to static variables
• RUNS ONLY ONCE WHEN IT THAT CLASS IS CALLED FOR THE FIRST TIME

Question 19

Static Inner Class

Answer 19

In java, we can create a class inside another class

Question 20

IQ: Why is main method static ? Related to psvm

Answer 20

• JRE can call the main method without creating object of the class.
• Static makes the values to be objects so they go into HEAP.

Ex: 
public class HelloWorld {
	    public static void main(String[] args) {
	        System.out.println("Hello World!");
			    }
			}

So that JRE can call it using. HelloWorld.main(null);