Cross-Language Class Checklist

Thomas J Kennedy

Contents:

1 Revisiting Cross-Language Class Checklist Rules

Revist our class checklist discussions, specifically the comparison of C++, Java and Python 3.

C++	Java	Python 3	Rust
Default Constructor	Default Constructor	`__init__`	`new()` or Default trait
Copy Constructor	Clone and/or Copy Constructor	`__deepcopy__`	Clone trait
Destructor
	finalize (deprecated/discouraged)	`__del__`	Drop trait
Assignment Operator (=)
Accessors (Getters)	Accessors (Getters)	Accessors (`@property`)	Accessors (Getters)
Mutators (Setters)	Mutators (Setters)	Setter (`@attribute.setter`)	Mutators (setters)
Swap
Logical Equivalence Operator (==)	equals	`__eq__`	std::cmp::PartialEq trait
Less-Than / Comes-Before Operator (<)	hashCode	`__hash__`	std::cmp::PartialOrd trait
Stream Insertion Operator (<<)	toString	`__str__`	std::fmt::Display trait
		`__repr__`	std::fmt::Debug trait
`begin()` and `end()`	`iterator`	`__iter__`	`iter()` and `iter_mut()`

Think about why so many parallels exist between languages that support Object Oriented Programming (OOP).

Think about RAII and the rule Every Constructor must intialize every attribute (data member).
- We will see this in Java with the deprecated/discouraged finalize and Python with the with context management mechanic.
Think about output in the context of operator<< in C++, toString in Java, __str__ in Python 3, and std::fmt::Display::fmt in Rust.
Think about the C++20 Three-Way Comparison (Spaceship operator).

2 Focusing on C++ & Java

Let us take our Class Checklist Comparison Table and focus only on C++ and Java.

Example 1: C++ & Java Class Checklist Table

C++ Java

Default Constructor Default Constructor

Copy Constructor Clone and/or Copy Constructor

Destructor

finalize (deprecated/discouraged)

Assignment Operator (=)

Accessors (Getters) Accessors (Getters)

Mutators (Setters) Mutators (Setters)

Swap

Logical Equivalence Operator (==) equals

Less-Than / Comes-Before Operator (<) hashCode

Stream Insertion Operator (<<) toString

begin() and end() iterator

C++	Java
Default Constructor	Default Constructor
Copy Constructor	Clone and/or Copy Constructor
Destructor
	finalize (deprecated/discouraged)
Assignment Operator (=)
Accessors (Getters)	Accessors (Getters)
Mutators (Setters)	Mutators (Setters)
Swap
Logical Equivalence Operator (==)	equals
Less-Than / Comes-Before Operator (<)	hashCode
Stream Insertion Operator (<<)	toString

`begin()` and `end()`	`iterator`

If we look at the table four rows (listed in bold) are immediately familiar:

Default Constructor - all objects need to be initialized to some default state.
Copy Constructor & clone - it must be possible to copy all objects.

clone allows dynamic binding to be leveraged (which is the standard in Java).
Accessors & Mutators - the principles of encapsulation still apply.

The only difference between C++ and Java for each of these items is syntax. The mechanics and conceptual approach are the same (barring a few pedantic differences).

Example 2: C++ & Java Class Checklist Table - The Remainder I

C++ Java

Destructor

finalize (deprecated/discouraged)

Assignment Operator (=)

Swap

Logical Equivalence Operator (==) equals

Less-Than / Comes-Before Operator (<) hashCode

Stream Insertion Operator (<<) toString

begin() and end() iterator

C++	Java
Destructor
	finalize (deprecated/discouraged)
Assignment Operator (=)
Swap
Logical Equivalence Operator (==)	equals
Less-Than / Comes-Before Operator (<)	hashCode
Stream Insertion Operator (<<)	toString

`begin()` and `end()`	`iterator`

If we strip out the four bolded rows, we are left with nine (9) rows. Let us tackle a few…

Destructor vs finalize - In C++ the destructor guarantees memory deallocation (e.g., calls to delete or delete[]).

It is also common to shoehorn in some RAII (e.g., closing a file). However, finalize is not equivalent or analogous to Destructors (in the general case).
Assignment Operator - Object variables in Java behave a lot like C++ smart pointers (mostly like std::shared_ptr). Java Garbage collection handles the rest.
Swap - In Java object variables are functionally fancy pointers. A Java swap is conceptaully a pointer swap.

We are left with…

Example 3: C++ & Java Class Checklist Table - The Remainder II

C++ Java

Logical Equivalence Operator (==) equals

Less-Than / Comes-Before Operator (<) hashCode

Stream Insertion Operator (<<) toString

begin() and end() iterator

C++	Java
Logical Equivalence Operator (==)	equals
Less-Than / Comes-Before Operator (<)	hashCode
Stream Insertion Operator (<<)	toString

`begin()` and `end()`	`iterator`

The next two rows are (in my opinion) more interesting:

operator== vs equals - barring a few mechanical differences these two functions are equivalent.
operator< and hashCode are not equivalent. However, they do serve similar purposes in each language’s built-in libraries.

We are now left with:

operator<< vs toString - these are both output functions (albeit with a few subtle differences).
begin and end vs iterator - iterators will be the focus of an upcoming lecture.