Beginning Java

Question 1

What are Java packages used for?

Answer 1

• Java packages are used to bundle related functionality and programs.

Question 2

What is this called? %s

Answer 2

• That is a format specifier.

Question 3

Why would you use %n instead of \n for a new line?

Answer 3

• The reason for this is that Windows and Unix based systems (Like Mac and Linux) use different newline sequences. %n makes the proper distinction.

Question 4

The exit method takes an argument for the status code as shown below. What does 0 mean?

• System.exit(0);

Answer 4

• The 0 argument means that the system exited intentionally.

Question 5

Primatives have special characteristics about the type of data that they can store, no methods or properties. What are the eight primative data types with Java?

Answer 5

• int
• double
• long
• byte
• char
• float
• short
• boolean

Question 6

Converting an integer to a string is also called what?

Answer 6

• Parsing an integer out of a string.
• Switching between types like this is also called casting.

Question 7

Look at the text below, what is Integer? What is parseInt()?

• int x = Integer.parseInt();

Answer 7

• Integer is a class
  
  • This is also known as a wrapper or a boxed type.
  • It provides methods for us to use.
• parseInt() is a static method of the Integer class.
• Here we are using the Integer class’ static method of parseInt() to generate a primative int.

Question 8

What does REPL stand for?

Answer 8

• Read Eval Print Loop

Question 9

What two things do all real world objects have?

Answer 9

• State and Behavior

Question 10

What is a blueprint used to create objects in Java?

Answer 10

• A class.

Question 11

What is special about the System class?

Answer 11

• The System class is automatically imported into a Java application.

Question 12

What does the System class provide to enable a developer to output information to the console? What is that thing called?

Answer 12

• It provides a static public field called out.
  
  • System.out
• out is a print stream and it exposes some methods that we have seen before for example: println.
  
  • System.out.println(“This is an example.”);

Question 13

What is a variable called that is defined in the scope of a class definition?

Answer 13

• A field or member variable.

Question 14

How do you mark a field or member variable as private?

Answer 14

• Put the private keyword before the type declaration.
• Example:
  
  • private String name = “Bob”;

Question 15

What is the most common way of exposing a class value, but not let someone set it?

Answer 15

• Add a method to your class.

Question 16

What are methods called that are used to get the state or field value of a class object?

Answer 16

• Getters.

Question 17

What are methods called that are used to change the state or set a field value?

Answer 17

• Setters.

Question 18

Why is a public method like a “getter” able to access a private field value?

Answer 18

• A public method is able to do so since it is defined within the scope of the class.

Question 19

What is a constructer?

Answer 19

• A constructer is a method that will run when you instantiate the class.
• It is also a great place to input information that can be used for initial creation of the object.

Question 20

When does instantiation happen?

Answer 20

• Instantiation happens when you create a new instance of the class, using the new keyword.

Question 21

How do you know that a method is in fact a constructer?

Answer 21

• It has the same name as the class and there is no return type.

Question 22

What is the structure of a method?

Answer 22

• access level modifer - Data Return Type - method name - parameters
• Example:
  
  • public String exampleMethodName(String parameterExample)

Question 23

What happens if no constructor is defined?

Answer 23

• A default constructor that takes no parameters is assumed and used.

Question 24

When using a constructor to set the values of a member variable the name of the variable passed into the constructor should be the same as that of the member variable that it is updating. How is confusion about the variable that is passed in and the actual member variable avoided?

Answer 24

• By employing the keyword this within the definition of a method or constructor.
• The variable which is prefixed with this is referring to the member variable.
• Example:
  
  • this.characterName = characterName;
• Alternatively some people use a different coding style and instead of this they prefix the member variable name with an m.
  
  • mCharacterName = characterName;

Question 25

What do you do when you want a variable to be assigned i.e. intialized once and only once?

Answer 25

• Define it using the final keyword.
• Example:
  
  • final private String characterName;

Question 26

How do you set a constant that you don’t want to be changed in your class?

Answer 26

• Constants that we want to be exposed would be set as public and to ensure they aren’t set to a different value the final keyword is used.
  
  • public final int EXAMPLE_CONSTANT = 12;
• If we want these variables to be accessible right off the class, class level variables, then we also add the static keyword.
  
  • public static final int MAX_PEZ = 12;

Question 27

What does the static keyword mean?

Answer 27

• It refers to how a variable is stored in memory.
• It allows you to have variables and methods available directly off your class (class-level) as opposed to have them be available off an instance (instance-level).

Question 28

What is used to make methods unique in Java?

Answer 28

• The name and the parameter list is used to make methods unique in Java.