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Questions tagged [pecs]

A java generics acronym for "Producer (uses) Extends, Consumer (uses) Super"

A good design pattern to follow when specifying java generic parameters is that the producers of objects specify their parameters as <T extends Something>, while the consumers of those same objects specify their parameters as <T super Something>.

See What is PECS (Producer Extends Consumer Super)? for more.

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PECS: How to convert a Consumer to a Producer?

I have a Restaurant that produces Meals. The kitchens is given plates that are Consumers. class Food{} class Bamboo extends Food {} interface Kitchen { void build(List dessert); } abstract class Restaurant { Kitchen…
Nicolas Zozol
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Java Generics (bounded wildcards)

According to the book "Effective Java" of Joshua Bloch there is a rule about how/when use the bounded wildcards in generics. This rule is PECS (Producer-Extends, Comsumer-Super). When I study the following example: Stack numberStack = new…
LiTTle
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Java's TreeSet.add() does not follow the PECS principle issue (Generics)

I have the following piece of code: public interface Segment extends Period { ... }; public class SegmentImpl_v1 implements Segment { ... }; public interface TimeLine> { ... }; public class TimeLineImpl
Jérôme Verstrynge
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Parametrize generic list whilst filtering and mapping

I'm trying to grasp PECS idea in java and don't know, how to apply this idea in following example: package org.example; import java.util.List; import java.util.Optional; interface Command { String name();} class DeleteCommand implements Command { …
mtw
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Kotlin and Java PECS

So my goal is use in Kotlin similar construction to Java PECS: List => MutableList When Jackson set after compiling data to this variable(list) it's ok. When I try to add item from Kotlin code ,…
faceoff
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Generics: LowerBounded wildcard vs UpperBounded wildcard

I understand the concept of PECS (Producer extends, Consumer super) but still have confusion regarding these notations: public class PECSTest { public static void main(String[] args) { //List ProducerList = new…
Manish
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How to give default value for a optional with generic type in JAVA

Thanks a lot for all the answers/comments! Apologize for the bad code sample I put in the original question. I was trying to simpify my question but apprently it ended up rather confusing. I changed the code a little bit: Map…
Sweden
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When to use PECS when designing a library?

I am working on a library which makes heavy use of functional interfaces and currently struggle whether to apply PECS or not: Predicate Function BiFunction vs. Predicate Function BiFunction
roookeee
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How can I type for Collection?

I have a method look like this. public void some(..., Collection collection) { // WOOT, PECS!!! final Stream stream = getStream(); stream.collect(toCollection(() -> collection)); } And how can I make this method…
Jin Kwon
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PECS parametrized class

I have a little piece of code where i created my own java.util.stream realization. I need to parametrize it using PECS rule. But either I didn't understand PECS rule well or my class designed bad - I don't know how to correctly implement it. When…
ruslangm
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Java: Working with Generics and Maps without Casting / @SuppressWarnings

I now came several times across this problem and always kinda solved this with some casts and @SuppressWarnings annotations. The relevant interfaces / abstract classes: public abstract class Data { } public interface DataOperations { boolean…
Benjamin M
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Overcoming generics put-get rule

I have read about the generics get and put rule that should prevent you from adding a Banana to a List: public abstract class Fruit { } public class Banana extends Fruit { } public class Apple extends Fruit { } List
Matthieu
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Java, generics and PECS: still having trouble understanding the C part; concrete example?

I'll post a single link here: Collections.sort(). There have been many posts on SO with regards to the PECS paradigm, including this one. In my own personal code, I use generics quite a lot, but have only ever had the use of the P part (that is,
fge
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Wildcard vs TypeParameter

class Employee { // valid } class Employee { // invalid } private static void test(List list1) { // valid } private static void test(List list1) { // invalid } what exactly…
user4811324
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How to remove 'unchecked' warning from my method?

I have following code private static class ParcelableParser { private ArrayList parse(List parcelables) { ArrayList parsedData = new ArrayList(); for(Parcelable parcelable : parcelables) { …
Bartosz Bilicki
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