Java-Specific Language Features

Question 1

prep code

Answer 1

A form of pseudocode, to help you focus on the logic without stressing about syntax

1. Instance variable declarations
2. Method declarations
3. Method logic

Question 2

Testing code

Answer 2

A class or methods that will test the real code and validate that it’s doing the right thing

Question 3

Real code

Answer 3

The actual implementation of the class.

Question 4

Coding strategy

Answer 4

1. Figure out what the class is supposed to do
2. List the instance variables and method
3. Write prepcode for the methods
4. Write test code for the methods
5. Implement the class
6. Test the methods
7. Debug and reimplement as needed
8. Express gratitude that we don’t have to test our learning experience app on actual live users

Question 5

What happens in Integer.parseInt() if the thing you pass isn’t a number? And does it recognize spelled-out numbers, like “three”?

Answer 5

Integer.parseInt() works only on Strings that represent the ascii values for digits (0, 1, 2,3, 4, 5, 6, 7, 8, 9). If you try to parse something like “two”, the code will blow up at runtime

Question 6

Difference between for and while

Answer 6

A while loop has only the boolean test; it doesn’t have a built-in initialization or iteration.
If you know how many times to loop, a for loop is cleaner

Question 7

Enhance for loop

Answer 7

Easier to iterate over all the elements in an array

Question 8

Casting primitives

Answer 8

A long is bigger than an int and the compiler can’t be sure where that long has been

Question 9

ArrayList vs. Array

Answer 9

1. A plain old array has to know its size at the time it’s created
2. Arrays use array syntax that’ s not used anywhere else in Java
3. To put an object in a regular array, you must assign it to a specific location

Question 10

Non Short Circuit Operators (&, |)

Answer 10

When used in boolean expressions, the & and | operators act like their && and “” counterparts, except that they force the JVM to always check both sides of the expression

Question 11

Package

Answer 11

1. Help the overall organization of a project or library
2. Give you a name-scoping, to help prevent collisions if you and 12 other programmers in your company all decide to make a class with the same name
3. Provide a level of security, because you can restrict the code you write so that only other classes in the same package can access it

Question 12

How does a full-name really help package? What’s to prevent two people from giving a class the same package name?

Answer 12

Java has a naming convention that usually prevents this from happening, as long as developers adhere to it

Question 13

Does import make my class bigger? Does it actually compile the imported class or package into my code?

Answer 13

1. Import only saves you from typing

2. Import is simply the way you give Java the full name of a class

Question 14

How come I never had to import the String class?

Answer 14

Because java.lang package sort of “pre-imported” for free

Question 15

Inheritance

Answer 15

1. The subclass inherits from the superclass

2. Subclass extends the superclass

Question 16

Subclass

Answer 16

1. The subclass can add new methods and instance variables of its own, and it can override the methods it inherits from the superclass
2. A subclass can only extends from one superclass

Question 17

Why isn’t Instance variable overriden

Answer 17

Because they don’t need to be. They don’t define any special behaviors, so a subclass can give an inherited instance variable any value it chooses

Question 18

What if the superclass wants to use the subclass version of the method?

Answer 18

No, there’s no sort of reverse or backward inheritance

Question 19

What if I want to use BOTH the superclass version and my overriding subclass version of a method?

Answer 19

we can do so using super.method(), which calls the inherited version, then comes back to do your own subclass-specific code

Question 20

Are there any practical limits on the levels of subclassing? How deep can you go?

Answer 20

Most are no more than one or two levels deep. It usually makes more sense to keep your inheritance trees shallow

Question 21

Can you make a method final, without making the whole class final?

Answer 21

If you want to protect a specific method from being overridden, mark the method with the final modifier.

Mark the whole class as final if you want to guarantee that none of the methods in that class will ever be overridden

Question 22

Why would you ever want to make a final class?

Answer 22

A final class prevent from overriden

Question 23

Overload method

Answer 23

A different method that happens to have the same method name. It has nothing to do with inheritance and polymorphism

Question 24

Concrete class

Answer 24

Those that are specific enough to be instantiated

Question 25

Abstract method

Answer 25

1. No use, no value, no purpose in life, unless it is extended
2. Must be overridden
3. Implementing an abstract method is just like overriding a method

Question 26

Abstract class

Answer 26

1. You can mix both abstract and non-abstract methods in the abstract class

Question 27

Abstract vs. Inheritance

Answer 27

Abstract method is that even though you haven’t put in any actual method, you’ve still defined part of the protocol for a group of subtypes

Question 28

Is class Object abstract?

Answer 28

No. Object is a non-abstract class because it’s got method implementation code that all class can inherit and use out-of-the-box, without having to override the mehtods

Question 29

Compiler

Answer 29

Check the class of the reference type-not the object type-to see if you can call a method using that reference

Question 30

Polymorphism

Answer 30

Many form

Question 31

Interface

Answer 31

1. Solve multiple inheritance problem by giving you much of the polymorphic benefits of multiple inheritance without the pain
2. A class can implement multiple interfaces
3. A class that implements an interface must implement all the methods of the interface, since all interface methods are implicitly public and abstract

Question 32

Super

Answer 32

The keyword super lets you invoke a superclass version of an overridden method, from within the subclass

Question 33

Stack

Answer 33

1. Where method invocations and local variables live

2. The method on the top of the stack is always the currently executing method

Question 34

Heap

Answer 34

Where all objects live

Question 35

Instance variables

Answer 35

Declared inside a class but no inside a method. They represent the “fields” that each individual object has

Question 36

Local variables

Answer 36

Declared inside a method, including method parameters. They’re temporary, and live only as long as the method is on the stack

Question 37

Local variables

Answer 37

Declared inside a method, including method parameters. They’re temporary, and live only as long as the method is on the stack

Question 38

Constructor

Answer 38

The code that runs when you instantiate an object

Question 39

Are constructors inherited? If you don’t provide a constructor but your superclass does do you get the superclass constructor instead of the default?

Answer 39

No. Constructors are not inherited. We’ll look at that in just a few pages

Question 40

“this” method

Answer 40

1. Use this() to call a constructor from another overloaded constructor in the same class
2. A constructor can have a call to super() OR this(), not both
3. this() can be used only in a constructor

Question 41

“this” method

Answer 41

1. Use this() to call a constructor from another overloaded constructor in the same class
2. A constructor can have a call to super() OR this(), not both
3. this() can be used only in a constructor

Question 42

Reference variables

Answer 42

Can be used only when it’s in scope