{"id":413,"date":"2019-05-28T01:41:26","date_gmt":"2019-05-28T01:41:26","guid":{"rendered":"http:\/\/www.onux.com\/jspp\/blog\/?p=413"},"modified":"2019-05-28T01:41:26","modified_gmt":"2019-05-28T01:41:26","slug":"tips-tricks-object-oriented-sorting-in-jspp-with-icomparable-t","status":"publish","type":"post","link":"https:\/\/www.onux.com\/jspp\/blog\/tips-tricks-object-oriented-sorting-in-jspp-with-icomparable-t\/","title":{"rendered":"Tips & Tricks: Object-oriented Sorting in JS++ with IComparable<T>"},"content":{"rendered":"

JS++ makes object-oriented sorting easy with the IComparable<T><\/a> interface and the Comparison enumeration<\/a> for type-safe (and readable) comparisons.<\/p>\n

Here’s the code. (Don’t worry; I’ll dissect it.)<\/p>\n

\r\nimport System;\r\n\r\nclass Employee : IComparable<Employee>\r\n{\r\n    private string firstName;\r\n    private string lastName;\r\n\r\n    public Employee(string firstName, string lastName) {\r\n        this.firstName = firstName;\r\n        this.lastName = lastName;\r\n    }\r\n\r\n    public Comparison compare(Employee that) {\r\n        \/\/ Sort by employee surname\r\n        return this.lastName.compare(that.lastName);\r\n    }\r\n\r\n    public override string toString() {\r\n    \treturn this.firstName + \" \" + this.lastName;\r\n    }\r\n}\r\n\r\nEmployee zig  = new Employee(\"Zig\", \"Ziglar\");\r\nEmployee john = new Employee(\"John\", \"Smith\");\r\nEmployee abe  = new Employee(\"Abe\", \"Lincoln\");\r\n\r\nEmployee[] employees = [ zig, john, abe ];\r\nemployees.sort();\r\nConsole.log(employees.join(\", \"));\r\n\r\n\/\/ Output:\r\n\/\/ Abe Lincoln, John Smith, Zig Ziglar\r\n<\/pre>\n
This is beautiful, object-oriented code. All of the custom sorting logic is one line of code. Let’s break down how that happens step-by-step.<\/p>\n
1. Implement IComparable<T><\/h3>\n
The first step is to implement the IComparable<T> interface. The interface provides only one method to implement: compare<\/a>.<\/p>\n
compare<\/code> expects the Comparison<\/a> enumeration as a result. As we can see from the documentation, Comparison<\/code> can have three possible results: LESS_THAN, GREATER_THAN, and EQUAL. While Java\/C# expect -1, 0, and 1, JS++ gives you type-safe and readable<\/em> comparisons.<\/p>\n
IComparable<T> and Comparison form the basis for custom sorting.<\/p>\n
2. Determine how to sort<\/h3>\n
We want to sort Employee<\/code> objects based on the employee’s last name. In order to do this, we want to compare strings and sort in alphabetical order. While we can do this manually, the JS++ Standard Library already provides these comparisons for us for primitive types.<\/p>\n
All primitive types in JS++ are auto-boxed. (Don’t worry, it gets optimized away.) In addition, all primitive types implement IComparable<T> (which provides the compare<\/code> method).<\/p>\n
Thus, since all primitive types provide the compare<\/code> method, sorting is as easy as this one line of code:<\/p>\n
return this.lastName.compare(that.lastName);<\/pre>\n
This is calling the System.String.compare<\/code><\/a> method, which compares strings lexicographically (in alphabetical order). (Likewise, if you wanted to compare by employee ID number, you might declare an unsigned int<\/code> and use System.UInteger32.compare<\/a>.)<\/p>\n
Thus, our sorting code and implementation of IComparable<T>.compare is just:<\/p>\n
\r\npublic Comparison compare(Employee that) {\r\n    \/\/ Sort by employee surname\r\n    return this.lastName.compare(that.lastName);\r\n}\r\n<\/pre>\n
3. Define toString() Behavior<\/h3>\n
In addition, we want to be able to easily visualize our sorted arrays. Therefore, we should define how our Employee<\/code> class looks when converted to a string so we can easily call System.Console.log<\/code> on it.<\/p>\n
JS++ internal types use a “unified type system” where everything inherits from System.Object<\/a>. If we look at the System.Object.toString<\/code> documentation, we can see that System.Object.toString<\/code> is a virtual<\/code> method based on its signature:<\/p>\n
public virtual string toString()<\/pre>\n
We override it with this code:<\/p>\n
\r\npublic override string toString() {\r\n    return this.firstName + \" \" + this.lastName;\r\n}\r\n<\/pre>\n
Thus, whenever we want a string representation of our Employee<\/code> object, we will get the employee’s first name followed by his last name. This will help us visualize our sorted employees.<\/p>\n
4. Instantiate some Employees<\/h3>\n
The next lines of code instantiate the Employee<\/code> class and inserts them in an array:<\/p>\n
\r\nEmployee zig  = new Employee(\"Zig\", \"Ziglar\");\r\nEmployee john = new Employee(\"John\", \"Smith\");\r\nEmployee abe  = new Employee(\"Abe\", \"Lincoln\");\r\n\r\nEmployee[] employees = [ zig, john, abe ];\r\n<\/pre>\n
Currently, the array is unsorted, and “Zig Ziglar” will be the first element.<\/p>\n
5. Sort the Array<\/h3>\n
Sorting is as simple as one line of code:<\/p>\n
employees.sort();<\/pre>\n
It’s just one line of code because we implemented IComparable<T>. Instead of implementing IComparable<T>, we could have also used the other overload of Array.sort<\/a>, which expects a callback:<\/p>\n
\r\nemployees.sort(Comparison(Employee a, Employee b) {\r\n    return a.lastName.compare(b.lastName);\r\n});\r\n<\/pre>\n
The callback allows flexibility; for example, you may choose to sort by employee first name in some cases.<\/p>\n
Implementing IComparable<T> simply provides a default sort so you can use System.Array.sort without a callback. These are the signatures for the System.Array.sort overloads:<\/p>\n
public T[] sort() where T: IComparable<T><\/code>
\npublic T[] sort(Comparison(T element1, T element2) comparator)<\/code><\/p>\n
Thus, if you do not provide a callback, you are using the overload that expects a class implementing IComparable<T>. If you try to sort objects whose respective classes do not implement the IComparable interface, you’ll receive an error:<\/p>\n
\r\n[  ERROR  ] JSPPE5056: System.Array.sort()' can only sort classes implementing 'IComparable'. Please implement 'IComparable' for `Employee' or use 'System.Array.sort(Comparison(T element1, T element2) comparator) at line 23 char 0 at test.js++\r\n<\/pre>\n
6. Print the Result<\/h3>\n
The final step is to just print the result:<\/p>\n
Console.log(employees.join(\", \"));<\/pre>\n
Et voila!<\/p>\n
(The toString<\/code> method we implemented earlier will get called for each element that gets joined. Thus, you get a readable output.)<\/p>\n","protected":false},"excerpt":{"rendered":"
JS++ makes object-oriented sorting easy with the IComparable<T> interface and the Comparison enumeration for type-safe (and readable) comparisons. Here’s the code. (Don’t worry; I’ll dissect it.) import System; class Employee : IComparable<Employee> { private string firstName; private string lastName; public Employee(string firstName, string lastName) { this.firstName = firstName; this.lastName = lastName; } public Comparison compare(Employee … Continue reading “Tips & Tricks: Object-oriented Sorting in JS++ with IComparable<T>”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[2,18],"tags":[],"_links":{"self":[{"href":"https:\/\/www.onux.com\/jspp\/blog\/wp-json\/wp\/v2\/posts\/413"}],"collection":[{"href":"https:\/\/www.onux.com\/jspp\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.onux.com\/jspp\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.onux.com\/jspp\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.onux.com\/jspp\/blog\/wp-json\/wp\/v2\/comments?post=413"}],"version-history":[{"count":21,"href":"https:\/\/www.onux.com\/jspp\/blog\/wp-json\/wp\/v2\/posts\/413\/revisions"}],"predecessor-version":[{"id":991,"href":"https:\/\/www.onux.com\/jspp\/blog\/wp-json\/wp\/v2\/posts\/413\/revisions\/991"}],"wp:attachment":[{"href":"https:\/\/www.onux.com\/jspp\/blog\/wp-json\/wp\/v2\/media?parent=413"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.onux.com\/jspp\/blog\/wp-json\/wp\/v2\/categories?post=413"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.onux.com\/jspp\/blog\/wp-json\/wp\/v2\/tags?post=413"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}