Java Fundamentals

Question 1

Class

Answer 1

A programmer-defined data type; a template for creating objects.

Question 2

Object

Answer 2

An instance of a class

Question 3

Variable

Answer 3

A user defined memory location. This is akin to referring to a physical location as Empire State Building instead of 20 W 34th St, New York, NY 10001.

Question 4

Methods

Answer 4

The actions performed by an object. They are comprised of a sequence of statements that has a name, may have parameter variables, and may return a value. A method can be invoked any number of times, with different values for its parameter variables.

Question 5

Initialize

Answer 5

Set a variable to a well-defined value when it is created.

Question 6

Assignment

Answer 6

Placing a new value into a variable.

Question 7

Case sensitive

Answer 7

Distinguishing upper- and lowercase characters. Java is a case sensitive language.

Question 8

Reserved words

Answer 8

A word that has a special meaning in a programming language and therefore cannot be used as a name by the programmer.

Question 9

Comments

Answer 9

An explanation to help the human reader understand a section of a program; ignored by the compiler.

There are two main types:

1. JavaDoc comments - These can be read by someone separately from the code (can also be used for multi-line comments) and are expected to be present before each Class definition and method header.
   /**
   * This is a JavaDoc comment
   */
2. Internal comments - These are only read in the code and are typically used for single line comments.
   // This is an internal comment

Question 10

uninitialized variable

Answer 10

A variable that has not been set to a particular value. In Java, using an uninitialized local variable is a syntax error.

Question 11

Public interface

Answer 11

The features (methods, variables, and nested types) of a class that are accessible to all clients.

Question 12

argument

Answer 12

A value supplied in a method call, or one of the values combined by an operator.

Question 13

void

Answer 13

A reserved word indicating no return type or an unknown type.

Question 14

Overloading

Answer 14

Giving more than one meaning to a method name.

Question 15

Accessor method

Answer 15

A method that accesses an object and returns some information about it, but does not change it. For example, the length method of the String class is an accessor method since it returns the length of the string without modifying it. Similarly, “getter” methods are also accessor methods since they return information without changing any data.

Question 16

mutator method

Answer 16

A method that changes the state of an object.

Question 17

API documentation

Answer 17

Information about each class in the Java library.

Question 18

Packages

Answer 18

A collection of related classes. The import statement is used to access one or more classes in a package.

Question 19

Object reference

Answer 19

A value that denotes the location of an object in memory. In Java, a variable whose type is a class contains a reference to an object of that class.

Question 20

Inner class

Answer 20

A class that is defined inside another class.

Question 21

Literal

Answer 21

A value that is written into the code of the program

Question 22

Self-documenting programs

Answer 22

Programs that can be understood just be reading their code. Clearly naming variables is one way to do this.

Question 23

Statically typed language

Answer 23

Java is a statically typed language which means that anytime you use a variable you need to tell the computer what type of data you’ll be storing in that variable.

Question 24

Named constants

Answer 24

A value that cannot be changed by a program. In Java, constants are defined with the reserved word final. It is convention to write such variable names in all uppercase letters.
For example:
final double INTEREST_RATE = 0.069;

Question 25

prompt

Answer 25

A string that tells the user to provide input.

Question 26

string

Answer 26

A sequence of characters.

Question 27

literals

Answer 27

A notation for a fixed value in a program, such as –2, 3.14, 6.02214115E23, “Harry”, or ‘H’.

Question 28

Unicode

Answer 28

A standard code that assigns code values consisting of two bytes to characters used in scripts around the world. Java stores all characters as their Unicode values.

Question 29

Escape sequence

Answer 29

Starts with the backslash character ( \ ) and is followed by one of more control characters that allow you to control the way that output is displayed. For example, the escape sequence that causes the output cursor to go to the next line is \n.

For example:
System.out.println(“These are the top sellers:\n”);
System.out.println(“Butter\nMilk\nSugar”);
Will print:
These are the top sellers:
Butter
Milk
Sugar

Question 30

Common escape sequences / characters

Answer 30

• *\n** - Newline: Advances the cursor to the next line
• *\t** - Horizontal tab: Moves cursor to the next tab stop
• *\b** - Backspace: Moves cursor back or left one space
• *\r** - Return: Moves cursor to the beginning of current line
• *\** - Backslash: Prints a backslash
• *'** Single quote: Prints a single quote
• *"** Double quote: Prints a double quote

Question 31

Camel casing

Answer 31

A way of naming variables/methods such that each word after the first begins with a capital letter and there is no punctuation in between the different words. For example, studentStudyHall is camel cased and proper Java convention.

Question 32

What is the difference between an instance method and a static method?

Answer 32

Instance methods operate on objects whereas static methods do not. For example, in Java numbers are not objects so you can never invoke a method on a number. Instead, you pass a number as an argument (explicit parameter) to a method, enclosing the number in parentheses are the method name:
double root = Math.sqrt( 9 );

Question 33

Scope of a variable

Answer 33

Where a variable can be accessed or used, which is based on the area of code in which it is defined. For example, if you want to count the iterations of a loop and return the value after the loop has ended, then you need to declare the variable outside of the loop (before it begins) so you can use it both inside and outside that block of code. As a result, there can be more than one variable with the same name as long as they have different scopes.

Question 34

Concatenation

Answer 34

The operation of joining character strings. For example, the concatenation of “comp” and “ute” is “compute”.

Question 35

Parameters

Answer 35

Parameters are used to pass information to a method. There are two main types:

1. Implicit - The object on which a method is invoked. For example, in the call f.x(y), the object x is the implicit parameter of the method f.
2. Explicit - A parameter of a method other than the object on which it’s invoked. In the example above, y is the explicit parameter of the method f. However, note that a method does not have to have explicit parameters!

Question 36

Instance method

Answer 36

A method with an implicit parameter; that is, a method that is invoked on an instance of a class.

Question 37

Instance of a class

Answer 37

An object whose type is that class.