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โ˜• JAVA TRICK: Creating and chaining Comparators

ยท java

Comparator factory and combination method ?

๐Ÿ‘‰ To compare longs, doubles, floats, and the like, use a method reference to their static '๐œ๐จ๐ฆ๐ฉ๐š๐ซ๐ž' method:

๐ถ๐‘œ๐‘š๐‘๐‘Ž๐‘Ÿ๐‘Ž๐‘ก๐‘œ๐‘Ÿ<๐ผ๐‘›๐‘ก๐‘’๐‘”๐‘’๐‘Ÿ> ๐‘๐‘œ๐‘š๐‘๐‘Ž๐‘Ÿ๐‘Ž๐‘ก๐‘œ๐‘Ÿ = ๐ผ๐‘›๐‘ก๐‘’๐‘”๐‘’๐‘Ÿ::๐‘๐‘œ๐‘š๐‘๐‘Ž๐‘Ÿ๐‘’;

๐Ÿ‘‰ If you want to compare objects by one of their attribute, pass a function extracting it to the static method '๐‚๐จ๐ฆ๐ฉ๐š๐ซ๐š๐ญ๐จ๐ซ.๐œ๐จ๐ฆ๐ฉ๐š๐ซ๐ข๐ง๐ ':

๐ถ๐‘œ๐‘š๐‘๐‘Ž๐‘Ÿ๐‘Ž๐‘ก๐‘œ๐‘Ÿ<๐‘†๐‘ก๐‘Ÿ๐‘–๐‘›๐‘”> ๐‘๐‘œ๐‘š๐‘๐‘Ž๐‘Ÿ๐‘Ž๐‘ก๐‘œ๐‘Ÿ = ๐ถ๐‘œ๐‘š๐‘๐‘Ž๐‘Ÿ๐‘Ž๐‘ก๐‘œ๐‘Ÿ.๐‘๐‘œ๐‘š๐‘๐‘Ž๐‘Ÿ๐‘–๐‘›๐‘”(๐‘†๐‘ก๐‘Ÿ๐‘–๐‘›๐‘”::๐‘™๐‘’๐‘›๐‘”๐‘กโ„Ž);

๐Ÿ‘‰ To first sort by one and then another attribute, create both comparators, then chain them with the instance method '๐ญ๐ก๐ž๐ง๐‚๐จ๐ฆ๐ฉ๐š๐ซ๐ข๐ง๐ ':

๐ถ๐‘œ๐‘š๐‘๐‘Ž๐‘Ÿ๐‘Ž๐‘ก๐‘œ๐‘Ÿ <๐‘ˆ๐‘ ๐‘’๐‘Ÿ> ๐‘๐‘ฆ๐น๐‘–๐‘Ÿ๐‘ ๐‘ก๐‘›๐‘Ž๐‘š๐‘’๐‘‡โ„Ž๐‘’๐‘›๐ฟ๐‘Ž๐‘ ๐‘ก๐‘๐‘Ž๐‘š๐‘’ = ๐‘๐‘ฆ๐น๐‘–๐‘Ÿ๐‘ ๐‘ก๐‘๐‘Ž๐‘š๐‘’.๐‘กโ„Ž๐‘’๐‘›๐ถ๐‘œ๐‘š๐‘๐‘Ž๐‘Ÿ๐‘–๐‘›๐‘”(๐‘๐‘ฆ๐ฟ๐‘Ž๐‘ ๐‘ก๐‘๐‘Ž๐‘š๐‘’);

๐Ÿ‘‰ Need an instances '๐‚๐จ๐ฆ๐ฉ๐š๐ซ๐š๐ญ๐จ๐ซ' that uses a '๐‚๐จ๐ฆ๐ฉ๐š๐ซ๐š๐›๐ฅ๐ž''s '๐œ๐จ๐ฆ๐ฉ๐š๐ซ๐ž๐“๐จ' method?

The static factory method '๐ง๐š๐ญ๐ฎ๐ซ๐š๐ฅ๐Ž๐ซ๐๐ž๐ซ' is there for you:

๐ถ๐‘œ๐‘š๐‘๐‘Ž๐‘Ÿ๐‘Ž๐‘ก๐‘œ๐‘Ÿ.๐‘›๐‘Ž๐‘ก๐‘ข๐‘Ÿ๐‘Ž๐‘™๐‘‚๐‘Ÿ๐‘‘๐‘’๐‘Ÿ();

If that's the wrong way around, just call '๐ซ๐ž๐ฏ๐ž๐ซ๐ฌ๐ž๐' on it:

๐‘ ๐‘ก๐‘Ÿ๐‘–๐‘›๐‘”.๐‘ ๐‘œ๐‘Ÿ๐‘ก(๐‘๐‘ฆ๐ฟ๐‘’๐‘›๐‘”๐‘กโ„Ž๐‘‡โ„Ž๐‘’๐‘›๐ด๐‘™๐‘โ„Ž๐‘Ž๐‘๐‘’๐‘ก๐‘–๐‘๐‘Ž๐‘™๐‘™๐‘ฆ.๐‘Ÿ๐‘’๐‘ฃ๐‘’๐‘Ÿ๐‘ ๐‘’๐‘‘());

๐Ÿ‘‰ Ah, and what to do about '๐ง๐ฎ๐ฅ๐ฅ' ?

Don't worry ! Just pass a '๐‚๐จ๐ฆ๐ฉ๐š๐ซ๐š๐ญ๐จ๐ซ' to '๐ง๐ฎ๐ฅ๐ฅ๐ฌ๐…๐ข๐ซ๐ฌ๐ญ' or '๐ง๐ฎ๐ฅ๐ฅ๐ฌ๐‹๐š๐ฌ๐ญ' to get a '๐‚๐จ๐ฆ๐ฉ๐š๐ซ๐š๐ญ๐จ๐ซ' that does what you need:

๐ถ๐‘œ๐‘š๐‘๐‘Ž๐‘Ÿ๐‘Ž๐‘ก๐‘œ๐‘Ÿ<๐ผ๐‘›๐‘ก๐‘’๐‘”๐‘’๐‘Ÿ> ๐‘›๐‘Ž๐‘ก๐‘ข๐‘Ÿ๐‘Ž๐‘™๐‘œ๐‘Ÿ๐‘‘๐‘’๐‘Ÿ๐‘๐‘ข๐‘™๐‘™๐‘ ๐ฟ๐‘Ž๐‘ ๐‘ก = ๐ถ๐‘œ๐‘š๐‘๐‘Ž๐‘Ÿ๐‘Ž๐‘ก๐‘œ๐‘Ÿ.๐‘›๐‘ข๐‘™๐‘™๐‘ ๐ฟ๐‘Ž๐‘ ๐‘ก(๐‘›๐‘Ž๐‘ก๐‘ข๐‘Ÿ๐‘Ž๐‘™๐‘‚๐‘Ÿ๐‘‘๐‘’๐‘Ÿ());

 

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