Java Building Blocks

Question 1

class

Answer 1

A description of an object. A class in Java is defined in a source file with the .java extension and compiled into a file with the .class extension.

Question 2

object

Answer 2

A runtime instance of a class in memory

Question 3

members of a class

Answer 3

methods and fields

Question 4

Method Signature

Answer 4

The full declaration of a method

Question 5

/* */ vs. /** */

Answer 5

The first is a regular multiline comment, the second is a special Javadoc comment

Question 6

When you have two classes defined in the same java file, how many can be public?

Answer 6

1

Question 7

Java Virtual Machine (JVM)

Answer 7

Runs Java class files.

Question 8

main() method declaration

Answer 8

public static void main(String[] args)

Question 9

How to compile and run a program called Zoo.java

Answer 9

javac Zoo.java

java Zoo

Question 10

bytecode

Answer 10

Compiled Java code. Bytecode appears in files with the .class extension.

Question 11

access modifier

Answer 11

Defines what other code can refer to the code. Choices are private,
protected, public, and default (no modifier.)

Question 12

static

Answer 12

Binds a method or field to its class so it can be called by just the class name, as in, for example, Zoo.main(). Java doesn't need to create an object to call the main() method
Makes a variable shared across all instances of this class.

Question 13

What type does java read in arguments as by default?

Answer 13

String

Question 14

package

Answer 14

A grouping of classes, interfaces, enumerations, and annotated types.

Question 15

What is the package that is automatically imported?

Answer 15

java.lang

Question 16

default package

Answer 16

An unnamed package used when no package statement is present in the code. This is a special unnamed package that you should use only for throwaway code. In real life, always name your packages to avoid naming conflicts and to allow others to reuse your code.

Question 17

JAR file

Answer 17

Like a zip file of mainly Java class files.

Question 18

What return type does a constructor have?

Answer 18

None! Not even void

Question 19

Instance Initializers

Answer 19

Code blocks (between braces { }) outside of methods

Question 20

Code Block

Answer 20

Code between { }

Question 21

When creating a new object, when does the constructor run?

Answer 21

After all fields and instance initializer blocks have run

Question 22

Two types of data

Answer 22

Primitive types
and
Reference types

Question 23

byte type

Answer 23

8-bit integral value (whole number)

Question 24

short type

Answer 24

16-bit integral value (whole number)

Question 25

int type

Answer 25

32-bit integral value (whole number)

Question 26

long type

Answer 26

64-bit integral value (whole number) (should have a capital L at the end e.g. 463728642L)

Question 27

float type

Answer 27

32-bit floating point value (could be decimal) (must have the letter f after the number, e.g. 100.5f)

Question 28

double

Answer 28

64-bit floating point value (could be decimal)

Question 29

char type

Answer 29

16-bit Unicode value

Question 30

literal

Answer 30

A numeric, character, boolean, or String value that is typed into the code.

Question 31

How to specify using octal notation

Answer 31

prefix the number with 0 e.g. 017

Question 32

How to specify using hexadecimal notation

Answer 32

prefix the number with 0x e.g. 0xFF

Question 33

How to specify using binary notation

Answer 33

prefix the number with 0b e.g 0b10

Question 34

What can you use to separate a number into sections to make it easier to read?

Answer 34

Underscores

1000000 = 1_000_000

(cannot have _ at the beginning, ending, or right before or after a decimal point)

Question 35

Reference Type

Answer 35

Basically an object, conceptually kinda like a pointer

Question 36

What can be assigned the value “null”?

Answer 36

Reference types

Question 37

Is String a primitive or a reference type?

Answer 37

Reference type

Question 38

What can an identifier be made up of?

Answer 38

letters, numbers, $, or _

note: cannot start with a number

Question 39

identifier

Answer 39

The name of a variable, method, class, interface, or enum.

Question 40

local variable

Answer 40

A variable defined within a method

Question 41

instance variable

Answer 41

Variable outside of a method (also called fields)

Question 42

class variable

Answer 42

An instance variable with the word “static” before it, shared across multiple objects

Question 43

Which variables are given default values and which are not?

Answer 43

Instance and class variables are, and local variables are not

Question 44

Default value of boolean

Answer 44

false

Question 45

Default value of byte, short, int and long

Answer 45

0

Question 46

Default value of float and double

Answer 46

0.0

Question 47

Default value of objects

Answer 47

null

Question 48

Order of elements in a class

Answer 48

1) Package Declaration
2) Import Statements
3) Class Declaration
4) Field Declarations and Method Declarations

Question 49

heap

Answer 49

Represents a large pool of unused memory allocated to your Java application. All
objects in Java reside in the heap memory.

Question 50

When is an object considered to be no longer reachable and thus eligible for garbage collection?

Answer 50

1) The object no longer has any references pointing to it
or
2) All references to the object have gone out of scope

Question 51

finalize()

Answer 51

The method that gets called if the garbage collector tries to collect an object.
Could run 0 or 1 time

Question 52

Why is Java secure?

Answer 52

It runs in a virtual machine, the JVM. This creates a sandbox that makes it hard for Java code to do evil things to the computer it is running on.

Question 53

What may a variable name begin with?

Answer 53

The name must begin with a letter, $, or _

Question 54

Default value of boolean

Answer 54

false

Question 55

Default value of byte, short, int and long

Answer 55

0

Question 56

Default value of float and double

Answer 56

0.0

Question 57

Default value of objects

Answer 57

null

Question 58

Benefits of Java

Answer 58

1) Object Oriented: Java is an object-oriented language, which means all code is defined in classes and most of those classes can be instantiated into objects.
2) Encapsulation: Java supports access modifiers to protect data from unintended access and modification.
3) Platform Independent: A key benefit is that Java code gets compiled once rather than needing to be recompiled for different operating systems.
4) Robust: Prevents memory leaks by doing its own garbage collecting.
5) Secure: Java code runs inside the JVM. This creates a sandbox that makes it hard for Java code to do evil things to the computer it is running on.