Section 1
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What is a declaration?
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Last updated
6 years ago
Date created
Mar 14, 2020
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Section 1
(50 cards)
What is a declaration?
Associates a name with a value. This name can then be used to refer to the value in other code. It does not evaluate to a value. It binds a name (Test) to a value (empty object) Example object Test {}
What order are method calls evaluated?
left-to-right
What is a block?
sequence of expressions or declarations surrounded by braces. A block is also an expression: it executes each of its sub-expressions in order and returns the value of the last expression
How many times is the body expression of a field evaluated for an object?
Only once
What is substitution?
You can change how you write a program without changing the meaning of the program. Example 1 + 2 + 3 6
Infix operator
shorthand code that can be used if a method takes only one parameter
What is referential transparency?
You can replace an expression with its value without changing the meaning of the program 1 + 1 and 2 are interchangeable
How do you define a method in an object body expression?
def name(parameter: type, ...): resultType = bodyExpression
A class is a value.
FALSE There is a different namespace for classes
How many times is the body expression of a method evaluated for an object?
Every time the method is called
What are the two distinct stages that a Scala program goes through?
Compile-time and run-time
What is a method?
refer to computations that produce values
How do we interact with data?
call methods
How do you define a string literal?
'/'
How do you define a character literal?
"/"
What is the difference between the following: "Hello world!" println("Hello world!")
- println("Hello world!") evaluates to a unit - Cannot be used as part of a larger expression - Prints the value as a side-effect - "Hello world!" evaluates to a string - Can be used as part of a larger expression
All values in Scala are objects.
TRUE
What is the grand supertype of all Scala types?
Any
Scala has very few operators - almost everything is a method call
TRUE
What is a constructor?
allows us to pass parameters to new objects as we create them
What is the difference between a method and a field?
A field gives a name to a value, whereas a method gives a name to a computation that produces a value
What is a side-effect?
You cannot replace an expression with its value without changing the meaning of the program println("hi") and "hi" are not interchangeable
What happens at compile time?
does the program make sense? 1. Syntactically correct 2. Type must be checked
What is a field?
refer to values stored within an object
What is a singleton type?
A type created just for an object we've created.
How do you define a field in an object body expression?
val name = valueExpression
When are types checked in a program?
During compile-time
Unit
result of expressions that evaluate to no interesting value, such as printing to standard output using println
What is AnyVal?
supertype of all value types
What is an overloaded method?
Methods that are defined several times for different argument types. Scala determines which variant is needed Example object calc2 { def square(value: Double) = value * value def cube(value: Double) = value * square(value) def square(value: Int) = value * value def cube(value: Int) = value * square(value) }
Are methods values? Are they expressions?
Calls to methods are expressions, but methods themselves are not expressions.
Expressions
parts of a program that evaluate to a value
What is the syntax for declaring a field in an object?
val name: type = valueExpression
Using var in Scala is a good practice.
FALSE val is a much better choice, because it is immutable. When programming in Scala prefer immutable fields whenever possible.
String interpolation
Allows you to embed variable references and expressions in a string s"""Use braces for expressions: ${sc.version}. You can omit the braces when just using a variable: $sc However, watch for ambiguities like ${sc}andextrastuff"""
What happens at run time?
The computer performs the instructions provided in the program
How would you write "foo".take(1) in operator style?
"foo" take 1
When are Scala objects and classes loaded?
Not until they are referenced (lazy loading).
What happens if a type check fails?
The compilation fails and the program will not be ran
Literal expression
literally looks like what they evaluate to "hello world"
What are the two types under Any?
AnyVal and AnyRef
Why do you strive to avoid side effects?
Make the program easier to understand
What is lazy loading?
In Scala objects and classes aren't loaded until they are referenced by other code.
What do the parenthesis mean in the bit of code? // res10: Any = ( )
Unit
Types
express some restrictions on programs
What is a class?
template for creating objects that have similar methods and fields
Values
exist in the computer's memory and are what a running program manipulates
What type will this conditional evaluate to? if (1>2) "alien" else 2001
Any, because the types mismatch between the if and else block
Literal expression
represents a fixed value that stands for "itself" Example: 42
Arguments
control how the method works. A value you pass into a method
Section 2
(2 cards)