1-Building Blocks

Question 1

Java Development Kit(JDK)

Answer 1

contains the minimum software you need

Question 2

javac

Answer 2

Converts .java source files into .class bytecode

Question 3

What command converts .java source files into .class bytecode

Answer 3

javac

Question 4

java

Answer 4

executes the program

Question 5

What command executes the program?

Answer 5

java

Question 6

jar

Answer 6

Packages files together

Question 7

What command packages files together?

Answer 7

jar

Question 8

javadoc

Answer 8

Generates documentation

Question 9

What command generates documentation?

Answer 9

javadoc

Question 10

What are 2 primary elements of Java classes?

Answer 10

1.Methods (functions, procedures)
2.Fields (variables)

Question 11

What is an object?

Answer 11

A runtime instance of a class in memory.

Question 12

An object is often referred to?

Answer 12

As an instance.

Question 13

What does an instance represent?

Answer 13

A single representation of the class.

Question 14

What is a reference?

Answer 14

A variable that points to an object.

Question 15

What are methods and fields of a class called together?

Answer 15

Members

Question 16

What is a top-level type?

Answer 16

A data structure that can be defined independently within a source file/

Question 17

Is it possible to have 2 top-level types in the same file?

Answer 17

yes, at most on of those is allowed to be public. And the public top-level type needs to match the filename.

Question 18

What do you call the shortcut for both javac and java? for example java Zoo.java ...args

Answer 18

single-file source-code

Question 19

Naming conflicts: What if you need two Classes with the same name from different packages?

Answer 19

1. pick one to use in the import statement and use the other fully qualified class name.
   2.Use the fully qualified class name for both.

Question 20

Compiling with wildcards: how do you use an asterisk with javac command?

Answer 20

you specify to include all Java files in a directory, cannot be used to include subdirectories.

Question 21

compiling to another directory?

Answer 21

javac -d directoryname package/class.java

Question 22

how to run programs compiled to another directory?

Answer 22

java -cp/-classpath/–class-path directoryname packagename.Classname

Question 23

What are important javac options?

Answer 23

1. -cp <classpath></classpath>
2. -classpath <classpath></classpath>
3. –class-path <classpath></classpath>
4. -d <dir></dir>

Question 24

What are important java options?

Answer 24

1. -cp <classpath></classpath>
2. -classpath <classpath></classpath>
3. –class-path <classpath></classpath>

Question 25

What are important jar options?

Answer 25

1. -c (creates a new JAR file) --create 2. -v (prints details when working with JAR files --verbose 3. -f JAR filename --file 4. -C (Directory containing files to be used to create the JAR

Question 26

rules for what Java file contains

Answer 26

* Each file can contain only one public class * The filename must match the class name, including case, and have .java extension * If entry point for the program, must contain valid main() method.

Question 27

Which modifiers are optional in the next main() method: public final static void main(final String[] args) {}

Answer 27

Both final modifiers

Question 28

How do you call the following: java Zoo.java zoo | shortcut for: javac Zoo.java \n java Zoo Zoo

Answer 28

launching single-file source-code programs

Question 29

# Required? Package declaration | package abc;

Answer 29

No

Question 30

# Required? import statements | import java.util.*;

Answer 30

No

Question 31

# Required? Top-level type declaration | public class C

Answer 31

Yes

Question 32

# Required? Field declarations | int value;

Answer 32

No

Question 33

# Required? Method declarations | void method()

Answer 33

No

Question 34

# Where does it go? Package declaration | package abc;

Answer 34

First line in the file | excluding comments or blank lines

Question 35

# Where does it go? import statements | import java.util.*;

Answer 35

Immediately after the package (if present)

Question 36

# Where does it go? Top-level type declarations | public class C

Answer 36

Immediately after import statements (if any)

Question 37

# Where does it go? Field declarations | int value;

Answer 37

Any top-level element within a class.

Question 38

# Where does it go? Method declarations | void method()

Answer 38

Any top-level elemant within a class.

Question 39

# What is the Order of Initialization?

Answer 39

1. Fields and instance initializer blocks are run in the order in which they appear in the file. 2. Constructor runs after all fials and instance initializer blocks have run.

Question 40

# What are the built-in data types of Java? | primitives

Answer 40

1. boolean 2. byte 3. short 4. int 5. long 6. float 7. double 8. char

Question 41

# Type, min value, max value, default value and an example of: boolean

Answer 41

1. true or false 2. n/a 3. n/a 4. false 5. true

Question 42

# Type, min value, max value, default value and an example of: byte

Answer 42

1. 8-bit integral value 2. -128 3. 127 4. 0 5. 123

Question 43

# Type, min value, max value, default value and an example of: short

Answer 43

1. 16-bit integral value 2. -32768 3. 32767 4. 0 5. 123

Question 44

# Type, min value, max value, default value and an example of: int

Answer 44

1. 32-bit integral value 2. -2147483648 3. 2147483647 4. 0 5. 123

Question 45

# Type, min value, max value, default value and an example of: long

Answer 45

1. 64-bit integral value 2. -2⁶³ 3. 2⁶³ -1 4. 0L 5. 123L

Question 46

# Type, min value, max value, default value and an example of: float

Answer 46

1. 32-bit floating-point value 2. n/a 3. n/a 4. 0.0f 5. 123.45f

Question 47

# Type, min value, max value, default value and an example of: double

Answer 47

1. 64-bit floating-point value 2. n/a 3. n/a 4. 0.0 5. 123.456

Question 48

# Type, min value, max value, default value and an example of: char

Answer 48

1. 16-bit Unicode value 2. 0 3. 65535 4. \u0000 5. 'a'

Question 49

Is String a Primitive?

Answer 49

No. String is often mistaken for ninth primitive because Java includes built-in support for String literals and operators.

Question 50

Which types of data contain Java applications?

Answer 50

1. primitive types 2. reference types

Question 51

# What are: byte, short, int, long types used for?

Answer 51

integer values without decimal points

Question 52

How much bits are used by numeric types?

Answer 52

each type uses twice as many bits as the smaller similar type. | short uses twice as many bits as byte does.

Question 53

How do numeric types cover the negative range?

Answer 53

All of the numeric types are signed and reserve one of their bits to cover a negative range.

Question 54

What is required for a float?

Answer 54

The letter f or F, otherwise Java interprets a decimal value as a double.

Question 55

What is required for long?

Answer 55

The letter l or L, number without a decimal point without an l or L is interpreted as an int in most scenarios.

Question 56

What is de difference between short and char?

Answer 56

short is signed, a range across positive and negative integers. char is unsigned, strictly positive including 0.

Question 57

which other digit formats are allowed by Java?

Answer 57

1. Octal 2. Hexadecimal 3. Binary

Question 58

# How do you recognize: Octal?

Answer 58

0 as a prefix | 017

Question 59

# How do you recognize: Hexadecimal?

Answer 59

0x or 0X as a prefix | 0xFF

Question 60

# How do you recognize: Binary?

Answer 60

0b or 0B as a prefix | 0b10

Question 61

When using an underscore to make numbers more readable, where can't they go?

Answer 61

1. at the beginning of a literal 2. at the end of a literal 3. right before a decimal point 4. right after a decimal point

Question 62

In which ways can a value be assigned to a reference?

Answer 62

1. A reference can be assigned to another object of the same or compatible type. 2. A reference can be assigned to a new object using the new keyword.

Question 63

# What is the Wrapper class of boolean? And does it inherit Number?

Answer 63

Boolean No | Boolean.valueOf(true)

Question 64

What is the Wrapper class of byte? And does it inherit Number?

Answer 64

Byte yes | Byte.valueOf( (byte) 1)

Question 65

What is the Wrapper class of short? And does it inherit Number?

Answer 65

Short yes | Short.valueOf( (short) 1)

Question 66

What is the Wrapper class of int? And does it inherit Number?

Answer 66

Integer yes | Integer.valueOf(1)

Question 67

What is the Wrapper class of long? And does it inherit Number?

Answer 67

Long yes | Long.valueOf(1)

Question 68

What is the Wrapper class of float? And does it inherit Number?

Answer 68

Float yes | Float.valueOf( (float) 1.0)

Question 69

What is the Wrapper class of doubld? And does it inherit Number?

Answer 69

Double yes | Double.valueOf(1.0)

Question 70

What is the Wrapper class of char? And does it inherit Number?

Answer 70

Character No | Character.valueOf('c')

Question 71

What is essential whitespace?

Answer 71

Part of your string and is important to you.

Question 72

What is Incidental whitespace?

Answer 72

whitespace to make the code easier to read.

Question 73

# What does it mean in regular string and text block: \"

Answer 73

* Regular String: `"` * Text block: `"`

Question 74

# What does it mean in regular string and text block: \"""

Answer 74

* Regular String: `n/a - invalid` * Text block: `"""`

Question 75

# What does it mean in regular string and text block: \"""

Answer 75

* Regular String: `n/a - invalid` * Text block: `"""`