Methods and Encapsulation

Question 1

Order of method declaration components

Answer 1

1) Access Modifier (public, private, etc.)
2) Optional Specifier (final, static, etc.)
3) Return type
4) Method name
5) Parameter list
6) Optional Exception list (throws blahblah)
7) Method body

Question 2

What does the public access modifier mean?

Answer 2

The method can be called from any class.

Question 3

What does the private access modifier mean?

Answer 3

The method can only be called from within the same class.

Question 4

What does the protected access modifier mean?

Answer 4

The method can only be called from classes in the same package or subclasses.

Question 5

What is the default level of access for a method?

Answer 5

The method can only be called from classes in the same package.

Question 6

If you are using a vararg parameter, where must it go?

Answer 6

At the end of the list of parameters

Question 7

When you omit a vararg parameter from your method call, what does it pass by defualt?

Answer 7

An empty array

Question 8

What can you pass in as a vararg parameter?

Answer 8

Either an array or a comma separated list of items (that will then be converted to an array) (or null)

Question 9

If a method or variable is static, what does it mean?

Answer 9

It’s shared by the whole class basically, so you can call it like ClassName.method() or ClassName.var rather than needing a separate instance of the class. You can also use an instance of the variable to access static things, you just don’t have to. If you set that instance to null, it will still work when accessing static things!

Question 10

Can static methods refer to non-static methods and variables?

Answer 10

NO

However a non-static method or variable can reference a static method or variable

Question 11

How do we name static final variables?

Answer 11

All caps with underscores between words

Question 12

How can you make all variables declared in a block of code static?

Answer 12

static {
int var1 = 1;
int var2 = 2;
}

Question 13

When does the static initializer run?

Answer 13

When the class is first used

Question 14

Static Imports

Answer 14

Used to import static members of classes so that you don’t have to precede the method o variable name with the class name

import static java.util.Arrays.asList;

Question 15

Is Java pass-by-value or pass-by-reference and what does that mean?

Answer 15

It is a pass-by-value language, meaning with primitives a copy of the variable is made and the method receives that copy, so that changes made to the variable passed in are not actually being made to the original value passed in. Rather than passing it the actual reference to the variable, it’s merely using the literal value of it.

With objects however, that copy is still pointing to the same object so the changes will take effect as long as it’s just methods being called on them instead of pointing them to new objects. For example,

StringBuilder s = new StringBuilder();
changeString(s);

void changeString(StringBuilder sb) {
      sb.append("hello"); // makes change
      sb = "howdy"; // Doesn't make change
}

Question 16

Method Overloading

Answer 16

When a class contains multiple methods with the same name but different parameter lists.

Question 17

Order in which Java tries to match overloaded method calls

Answer 17

1) Exact match by type
2) Larger primitive type (long is larger than int for example)
3) Autoboxed type (Integer as opposed to int)
4) Varargs

Question 18

Default Constructor

Answer 18

A constructor without any parameters that is generated by the compiler when no constructors are coded.

Question 19

this()

Answer 19

You can use “this” as a method to call a constructor from within another constructor. Note: If you use this() it must be the first non-comment line in the constructor!

public Hamster(int weight) {
  this(weight, "brown");
}
public Hamster(int weight, String color) {     
   this.weight = weight;
   this.color = color;
  }

Question 20

Where are the three places you can initialize a final variable?

Answer 20

1) In-line when it is declared
2) In the static initializer block
3) In a constructor

Question 21

Order of Initialization

Answer 21

1) If there is a superclass, initialize it first
2) Static variable declarations and static initializers in the order they appear in the file

(Then main method starts)

3) Instance variable declarations and instance initializers in the order they appear in the file
4) The constructor

(p. 202)

Question 22

Encapsulation

Answer 22

Combining fields and methods together in a class such that the methods
operate on the data, as opposed to users of the class accessing the fields directly. (Getters and setters, etc.)

Question 23

JavaBean

Answer 23

A software component that makes it easy to reuse code.

Question 24

Where is the Predicate interface located?

Answer 24

java.util.function

Question 25

Functional Interface

Answer 25

An interface where you only implement one method.

These are the only interfaces you can use a lambda expression with

Question 26

How do you access the different elements of a varargs?

Answer 26

Just like arrays, so if you want the second element of a varargs called “nums”, then do nums[1]

Question 27

Is this code legal? why?

private static final ArrayList values = new ArrayList<>();
public static void main(String[] args) {
values.add(“changed”);
}

Answer 27

Yes, as long you don’t assign a final reference variable to a new object, you can change its qualities

Question 28

How many times can a parameter be converted when trying to find a method it fits with?

Answer 28

Once

let’s say there is a method

void number(Long l) {}

then calling number(4) won’t work because it would try to convert to a primitive long then autobox to Long and that is 2 conversions.

calling number(4L) works because it would just require the autoboxing