☕ JAVA TRICK: Creating and chaining Comparators

Comparator factory and combination method ?

👉 To compare longs, doubles, floats, and the like, use a method reference to their static '𝐜𝐨𝐦𝐩𝐚𝐫𝐞' method:

𝐶𝑜𝑚𝑝𝑎𝑟𝑎𝑡𝑜𝑟<𝐼𝑛𝑡𝑒𝑔𝑒𝑟> 𝑐𝑜𝑚𝑝𝑎𝑟𝑎𝑡𝑜𝑟 = 𝐼𝑛𝑡𝑒𝑔𝑒𝑟::𝑐𝑜𝑚𝑝𝑎𝑟𝑒;

👉 If you want to compare objects by one of their attribute, pass a function extracting it to the static method '𝐂𝐨𝐦𝐩𝐚𝐫𝐚𝐭𝐨𝐫.𝐜𝐨𝐦𝐩𝐚𝐫𝐢𝐧𝐠':

𝐶𝑜𝑚𝑝𝑎𝑟𝑎𝑡𝑜𝑟<𝑆𝑡𝑟𝑖𝑛𝑔> 𝑐𝑜𝑚𝑝𝑎𝑟𝑎𝑡𝑜𝑟 = 𝐶𝑜𝑚𝑝𝑎𝑟𝑎𝑡𝑜𝑟.𝑐𝑜𝑚𝑝𝑎𝑟𝑖𝑛𝑔(𝑆𝑡𝑟𝑖𝑛𝑔::𝑙𝑒𝑛𝑔𝑡ℎ);

👉 To first sort by one and then another attribute, create both comparators, then chain them with the instance method '𝐭𝐡𝐞𝐧𝐂𝐨𝐦𝐩𝐚𝐫𝐢𝐧𝐠':

𝐶𝑜𝑚𝑝𝑎𝑟𝑎𝑡𝑜𝑟 <𝑈𝑠𝑒𝑟> 𝑏𝑦𝐹𝑖𝑟𝑠𝑡𝑛𝑎𝑚𝑒𝑇ℎ𝑒𝑛𝐿𝑎𝑠𝑡𝑁𝑎𝑚𝑒 = 𝑏𝑦𝐹𝑖𝑟𝑠𝑡𝑁𝑎𝑚𝑒.𝑡ℎ𝑒𝑛𝐶𝑜𝑚𝑝𝑎𝑟𝑖𝑛𝑔(𝑏𝑦𝐿𝑎𝑠𝑡𝑁𝑎𝑚𝑒);

👉 Need an instances '𝐂𝐨𝐦𝐩𝐚𝐫𝐚𝐭𝐨𝐫' that uses a '𝐂𝐨𝐦𝐩𝐚𝐫𝐚𝐛𝐥𝐞''s '𝐜𝐨𝐦𝐩𝐚𝐫𝐞𝐓𝐨' method?

The static factory method '𝐧𝐚𝐭𝐮𝐫𝐚𝐥𝐎𝐫𝐝𝐞𝐫' is there for you:

𝐶𝑜𝑚𝑝𝑎𝑟𝑎𝑡𝑜𝑟.𝑛𝑎𝑡𝑢𝑟𝑎𝑙𝑂𝑟𝑑𝑒𝑟();

If that's the wrong way around, just call '𝐫𝐞𝐯𝐞𝐫𝐬𝐞𝐝' on it:

𝑠𝑡𝑟𝑖𝑛𝑔.𝑠𝑜𝑟𝑡(𝑏𝑦𝐿𝑒𝑛𝑔𝑡ℎ𝑇ℎ𝑒𝑛𝐴𝑙𝑝ℎ𝑎𝑏𝑒𝑡𝑖𝑐𝑎𝑙𝑙𝑦.𝑟𝑒𝑣𝑒𝑟𝑠𝑒𝑑());

👉 Ah, and what to do about '𝐧𝐮𝐥𝐥' ?

Don't worry ! Just pass a '𝐂𝐨𝐦𝐩𝐚𝐫𝐚𝐭𝐨𝐫' to '𝐧𝐮𝐥𝐥𝐬𝐅𝐢𝐫𝐬𝐭' or '𝐧𝐮𝐥𝐥𝐬𝐋𝐚𝐬𝐭' to get a '𝐂𝐨𝐦𝐩𝐚𝐫𝐚𝐭𝐨𝐫' that does what you need:

𝐶𝑜𝑚𝑝𝑎𝑟𝑎𝑡𝑜𝑟<𝐼𝑛𝑡𝑒𝑔𝑒𝑟> 𝑛𝑎𝑡𝑢𝑟𝑎𝑙𝑜𝑟𝑑𝑒𝑟𝑁𝑢𝑙𝑙𝑠𝐿𝑎𝑠𝑡 = 𝐶𝑜𝑚𝑝𝑎𝑟𝑎𝑡𝑜𝑟.𝑛𝑢𝑙𝑙𝑠𝐿𝑎𝑠𝑡(𝑛𝑎𝑡𝑢𝑟𝑎𝑙𝑂𝑟𝑑𝑒𝑟());