The C++ and Java Class Checklists

Thomas J. Kennedy

Contents:
1 Class Checklist as a Collection of Emergent Properties
2 Focusing on C++ & Java

1 Class Checklist as a Collection of Emergent Properties

The class checklist can be though of as a set of emergent properties (or, if you think as the table as a single entity, an emergent property).

Depending on your programming background you will be familiar with C++, Java (maybe both C++ and Java). Select (based on your background) either the C++ or Java column. Compare it to the Python column.

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) Setters (@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()

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

  2. Think about the rule Every Constructor must intialize every attribute (data member).

  3. Think about Resource Acquisition is Initialization (RAII) as defined by cppreference.com:

    Resource Acquisition Is Initialization or RAII, is a C++ programming technique[1][2] which binds the life cycle of a resource that must be acquired before use (allocated heap memory, thread of execution, open socket, open file, locked mutex, disk space, database connection—anything that exists in limited supply) to the lifetime of an object.

    • The Python with context management mechanic is an example of RAII.

  4. Think about output in the context of

    • operator<< in C++
    • toString in Java
    • __str__ in Python 3
    • std::fmt::Display::fmt in Rust

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

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

  1. Default Constructor - all objects need to be initialized to some default state.

  2. Copy Constructor & clone - it must be possible to copy all objects.

    clone allows dynamic binding to be leveraged (which is the standard in Java).

  3. 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

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

  1. 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).

  2. Assignment Operator - Object variables in Python (and Java) behave a lot like C++ smart pointers (mostly like std::shared_ptr). Python (or Java) Garbage collection handles the rest.

  3. Swap - In Python (and Java) object variables are functionally fancy pointers. A Python (or Java) swap is conceptually 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

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

  1. operator== vs equals - barring a few mechanical differences these two functions are equivalent.

  2. operator< and hashCode are not equivalent. However, they do serve similar purposes in each language’s built-in libraries.

We are now left with:

  1. operator<< vs toString - these are both output functions (albeit with a few subtle differences).

  2. begin and end vs iterator - iterators are the focus of a separate lecture.

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