☕ JAVA TRICK: Creating and chaining predicates

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☕ JAVA TRICK: Creating and chaining predicates

· java

You know how to write lambdas to create predicates,

but did you know that the interfaces offers a lot of methods to create and combine them?

𝐂𝐚𝐥𝐥 𝐭𝐡𝐞 𝐢𝐧𝐬𝐭𝐚𝐧𝐜𝐞 𝐦𝐞𝐭𝐡𝐨𝐝𝐬 '𝐚𝐧𝐝', '𝐨𝐫', '𝐧𝐞𝐠𝐚𝐭𝐞' 𝐟𝐨𝐫 𝐛𝐨𝐨𝐥𝐞𝐚𝐧 𝐟𝐨𝐫𝐦𝐮𝐥𝐚𝐬.

Predicate<String> isNull = Objects::isNull;
Predicate<String> isEmpty = String::isEmpty;
Predicate<String> isNullOrEmpty = isNull.or(isEmpty);
Predicate<String> isNotNullNorEmpty = isNullOrEmpty.negate();
Predicate<String> shorterThan5 = s -> s.length() < 5;
Predicate<String> p = isNotNullNorEmpty.and(shorterThan5);

𝐓𝐡𝐞 𝐟𝐚𝐜𝐭𝐨𝐫𝐲 𝐦𝐞𝐭𝐡𝐨𝐝 '𝐧𝐨𝐭' 𝐢𝐬 𝐠𝐫𝐞𝐚𝐭 𝐭𝐨 𝐢𝐧𝐯𝐞𝐫𝐭 𝐚 𝐦𝐞𝐭𝐡𝐨𝐝 𝐫𝐞𝐟𝐞𝐫𝐞𝐧𝐜𝐞.

Predicate<Collection<String>> isEmpty = Collection::isEmpty;
Predicate<Collection<String>> isNotEmpty = Predicate.not(isEmpty);

𝐀𝐧𝐝 𝐢𝐟 𝐲𝐨𝐮 𝐩𝐚𝐬𝐬 𝐬𝐨𝐦𝐞 𝐨𝐛𝐣𝐞𝐜𝐭 𝐭𝐨 '𝐢𝐬𝐄𝐪𝐮𝐚𝐥', 𝐲𝐨𝐮 𝐠𝐞𝐭 𝐚 𝐩𝐫𝐞𝐝𝐢𝐜𝐚𝐭𝐞 𝐭𝐡𝐚𝐭 𝐜𝐡𝐞𝐜𝐤𝐬 𝐢𝐧𝐭𝐚𝐧𝐜𝐞𝐬 𝐟𝐨𝐫 𝐞𝐪𝐮𝐚𝐥𝐢𝐭𝐲 𝐰𝐢𝐭𝐡 𝐢𝐭.

Predicate<String> isEqualToDuke = Predicate.isEqual("Duke");