{"id":199,"date":"2023-09-22T21:15:00","date_gmt":"2023-09-22T13:15:00","guid":{"rendered":"https:\/\/blog.bexonbai.com\/?p=199"},"modified":"2026-03-02T21:19:28","modified_gmt":"2026-03-02T13:19:28","slug":"java-map-lambda-the-alternative-forms-of-if-else","status":"publish","type":"post","link":"https:\/\/blog.bexonbai.com\/?p=199","title":{"rendered":"Java Map + lambda, the alternative forms of if-else"},"content":{"rendered":"\n

If your program has tons of if-eles<\/code> like this, maybe you could try rewriting it as Map + Function. Function can be turned into lambda form to make it look more elegant. \ud83d\ude01<\/p>\n\n\n\n

switch<\/strong> (<\/strong>type)<\/strong> {<\/strong>\n    case<\/strong> RANK:\n        searchRankBooks();<\/strong>\n        break<\/strong>;<\/strong>\n    case<\/strong> RECOMMENDATION:\n        searchRecommendationBooks();<\/strong>\n        break<\/strong>;<\/strong>\n    default<\/strong>:<\/strong>\n        new<\/strong> ArrayList<\/strong><>();<\/strong>\n        break<\/strong>;<\/strong>\n}<\/strong><\/code><\/pre>\n\n\n\n
Create a Map<String, Function<K, V>><\/code> in your service, use it to store if-else business functions.<\/p>\n\n\n\n
private<\/strong> Map<\/strong><<\/strong>String<\/strong>,<\/strong> Function<\/strong><<\/strong>TYPE,<\/strong> List<\/strong><<\/strong>String<\/strong>>>><\/strong> bookSearchTypeMap =<\/strong> new<\/strong> HashMap<\/strong><>();<\/strong><\/code><\/pre>\n\n\n\n
Init a Function as value, Function can be written as the lambda, like this\ud83d\udc47<\/p>\n\n\n\n
bookSearchTypeMap.<\/strong>put(<\/strong>RANK.<\/strong>name(),<\/strong> type -><\/strong> bookTypeService.<\/strong>rank(<\/strong>type));<\/strong><\/code><\/pre>\n\n\n\n
use a getResult(K)<\/code> to get results.<\/p>\n\n\n\n
public<\/strong> List<\/strong><<\/strong>String<\/strong>><\/strong> getResult<\/strong>(<\/strong>TYPE type)<\/strong> {<\/strong>\n    Function<\/strong><<\/strong>TYPE,<\/strong> List<\/strong><<\/strong>String<\/strong>>><\/strong> result =<\/strong> bookSearchTypeMap.<\/strong>get(<\/strong>type.<\/strong>name());<\/strong>\n    if<\/strong> (<\/strong>result !=<\/strong> null<\/strong>)<\/strong> {<\/strong>\n        return<\/strong> result.<\/strong>apply(<\/strong>type);<\/strong>\n    }<\/strong>\n    return<\/strong> new<\/strong> ArrayList<\/strong><>();<\/strong>\n}<\/strong><\/code><\/pre>\n\n\n\n
Called it in the Controller.<\/p>\n\n\n\n
public<\/strong> List<\/strong><<\/strong>String<\/strong>><\/strong> books<\/strong>(<\/strong>TYPE type){<\/strong>\n    return<\/strong> queryBookService.<\/strong>getResult(<\/strong>type);<\/strong>\n}<\/strong><\/code><\/pre>\n\n\n\n
Log:<\/p>\n\n\n\n
><\/strong> Task :Main.main()<\/strong>\nrank[Corpus Delicti, Die Insel der Tausend Leuchtt\u00fcrme, Dark Mirror Castle, Iron Flame \u2013 Flammengek\u00fcsst]\nrecommendation[Die Insel der Tausend Leuchtt\u00fcrme, Vergissmeinnicht - Was bisher verloren war, Dark Shadow Castle, Fighting Fate]<\/code><\/pre>\n\n\n\n
Here is just one way to implement it, you can rewrite it a bit to use it in any framework.<\/p>\n\n\n\n
\n
Happy Coding!<\/p>\n<\/blockquote>\n\n\n\n
Full Demo\ud83d\udc68\u200d\ud83d\udcbb<\/p>\n\n\n\n
public<\/strong> class<\/strong> QueryBookService<\/strong> {<\/strong>\n    private<\/strong> BookTypeService<\/strong> bookTypeService =<\/strong> new<\/strong> BookTypeService<\/strong>();<\/strong>\n    private<\/strong> Map<\/strong><<\/strong>String<\/strong>,<\/strong> Function<\/strong><<\/strong>TYPE,<\/strong> List<\/strong><<\/strong>String<\/strong>>>><\/strong> bookSearchTypeMap =<\/strong> new<\/strong> HashMap<\/strong><>();<\/strong>\n\n    public<\/strong> QueryBookService<\/strong>()<\/strong> {<\/strong>\n        bookSearchTypeMap.<\/strong>put(<\/strong>RANK.<\/strong>name(),<\/strong> type -><\/strong> bookTypeService.<\/strong>rank(<\/strong>type));<\/strong>\n        bookSearchTypeMap.<\/strong>put(<\/strong>RECOMMENDATION.<\/strong>name(),<\/strong> type -><\/strong> bookTypeService.<\/strong>recommendation(<\/strong>type));<\/strong>\n    }<\/strong>\n\n    public<\/strong> List<\/strong><<\/strong>String<\/strong>><\/strong> getResult<\/strong>(<\/strong>TYPE type)<\/strong> {<\/strong>\n        Function<\/strong><<\/strong>TYPE,<\/strong> List<\/strong><<\/strong>String<\/strong>>><\/strong> result =<\/strong> bookSearchTypeMap.<\/strong>get(<\/strong>type.<\/strong>name());<\/strong>\n        if<\/strong> (<\/strong>result !=<\/strong> null<\/strong>)<\/strong> {<\/strong>\n            return<\/strong> result.<\/strong>apply(<\/strong>type);<\/strong>\n        }<\/strong>\n        return<\/strong> new<\/strong> ArrayList<\/strong><>();<\/strong>\n    }<\/strong>\n}<\/strong><\/code><\/pre>\n\n\n\n
public<\/strong> class<\/strong> BookTypeService<\/strong> {<\/strong>\n    public<\/strong> List<\/strong><<\/strong>String<\/strong>><\/strong> rank<\/strong>(<\/strong>TYPE type){<\/strong>\n        return<\/strong> getRank<\/strong>(<\/strong>type);<\/strong>\n    }<\/strong>\n\n    public<\/strong> List<\/strong><<\/strong>String<\/strong>><\/strong> recommendation<\/strong>(<\/strong>TYPE type){<\/strong>\n        return<\/strong> getRecommendation<\/strong>(<\/strong>type);<\/strong>\n    }<\/strong>\n}<\/strong><\/code><\/pre>\n\n\n\n
public<\/strong> class<\/strong> BookSearchController<\/strong> {<\/strong>\n    private<\/strong> QueryBookService<\/strong> queryBookService =<\/strong> new<\/strong> QueryBookService<\/strong>();<\/strong>\n\n    public<\/strong> List<\/strong><<\/strong>String<\/strong>><\/strong> books<\/strong>(<\/strong>TYPE type){<\/strong>\n        return<\/strong> queryBookService.<\/strong>getResult(<\/strong>type);<\/strong>\n    }<\/strong>\n}<\/strong><\/code><\/pre>\n\n\n\n
public<\/strong> enum<\/strong> TYPE {<\/strong>\n    RANK,<\/strong> RECOMMENDATION\n}<\/strong><\/code><\/pre>\n\n\n\n
\/\/ Mocks<\/em>\npublic<\/strong> class<\/strong> BookMocks<\/strong> {<\/strong>\n    public<\/strong> static<\/strong> List<\/strong><<\/strong>String<\/strong>><\/strong> getRank<\/strong>(<\/strong>TYPE type)<\/strong> {<\/strong>\n        List<\/strong><<\/strong>String<\/strong>><\/strong> list =<\/strong> new<\/strong> ArrayList<\/strong><>();<\/strong>\n        list.<\/strong>add(<\/strong>\"Corpus Delicti\");<\/strong>\n        list.<\/strong>add(<\/strong>\"Die Insel der Tausend Leuchtt\u00fcrme\");<\/strong>\n        list.<\/strong>add(<\/strong>\"Dark Mirror Castle\");<\/strong>\n        list.<\/strong>add(<\/strong>\"Iron Flame \u2013 Flammengek\u00fcsst\");<\/strong>\n        return<\/strong> list;<\/strong>\n    }<\/strong>\n\n    public<\/strong> static<\/strong> List<\/strong><<\/strong>String<\/strong>><\/strong> getRecommendation<\/strong>(<\/strong>TYPE type)<\/strong> {<\/strong>\n        List<\/strong><<\/strong>String<\/strong>><\/strong> list =<\/strong> new<\/strong> ArrayList<\/strong><>();<\/strong>\n        list.<\/strong>add(<\/strong>\"Die Insel der Tausend Leuchtt\u00fcrme\");<\/strong>\n        list.<\/strong>add(<\/strong>\"Vergissmeinnicht - Was bisher verloren war\");<\/strong>\n        list.<\/strong>add(<\/strong>\"Dark Shadow Castle\");<\/strong>\n        list.<\/strong>add(<\/strong>\"Fighting Fate\");<\/strong>\n        return<\/strong> list;<\/strong>\n    }<\/strong>\n}<\/strong><\/code><\/pre>\n\n\n\n
public<\/strong> class<\/strong> Main<\/strong> {<\/strong>\n    public<\/strong> static<\/strong> void<\/strong> main<\/strong>(<\/strong>String<\/strong>[]<\/strong> args)<\/strong> {<\/strong>\n        BookSearchController<\/strong> controller =<\/strong> new<\/strong> BookSearchController<\/strong>();<\/strong>\n\n        System<\/strong>.<\/strong>out.<\/strong>println(<\/strong>\"rank\" +<\/strong> controller.<\/strong>books(<\/strong>RANK));<\/strong>\n        System<\/strong>.<\/strong>out.<\/strong>println(<\/strong>\"recommendation\" +<\/strong> controller.<\/strong>books(<\/strong>RECOMMENDATION));<\/strong>\n\n    }<\/strong>\n}<\/strong><\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"
An alternative form of if-else, provides an other way.<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7],"tags":[],"class_list":["post-199","post","type-post","status-publish","format-standard","hentry","category-develop"],"_links":{"self":[{"href":"https:\/\/blog.bexonbai.com\/index.php?rest_route=\/wp\/v2\/posts\/199","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blog.bexonbai.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blog.bexonbai.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blog.bexonbai.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.bexonbai.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=199"}],"version-history":[{"count":1,"href":"https:\/\/blog.bexonbai.com\/index.php?rest_route=\/wp\/v2\/posts\/199\/revisions"}],"predecessor-version":[{"id":200,"href":"https:\/\/blog.bexonbai.com\/index.php?rest_route=\/wp\/v2\/posts\/199\/revisions\/200"}],"wp:attachment":[{"href":"https:\/\/blog.bexonbai.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=199"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.bexonbai.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=199"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.bexonbai.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=199"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}