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POHow would I use generics in Java to create a generic interface that defines a method that only accepts the implementation as a parameter?
 

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  1. POHow would I use generics in Java to create a generic interface that defines a method that only accepts the implementation as a parameter?
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    <p>Is there a way to define a method in an interface where implementations can be typed to the implementing class? Here's a concrete example of my initial attempt to solve it, but I'll point out where it fails.</p> <pre><code>public interface ErrorMeasurable&lt;T extends ErrorMeasurable&lt;T&gt;&gt; { // I want every implementation of this method to accept // the implementing type as a parameter. I'm willing to accept // that programmers can maliciously type it to something else // that meets the type boundary. I'm not willing to accept // polymorphic usage to be verbose or strange as the below example shows. boolean approxEquals(T that); } // This works... public class MyDecimal implements ErrorMeasurable&lt;MyDecimal&gt; { boolean approxEquals(MyDecimal that) { ... } } // But polymorphism doesn't work well... public interface MyNumber&lt;T extends ErrorMeasurable&lt;T&gt;&gt; implements ErrorMeasurable&lt;T&gt; { boolean approxEquals(T that) { ... } } public class MyDecimal2 implements MyNumber&lt;MyDecimal&gt; { boolean approxEquals(MyDecimal that) { ... } } public class UsesNumbers { // PROBLEM 1: the type parameter is unbound. MyNumber rawNumber1, rawNumber2; // PROBLEM 2: This binds the type parameter but it is hard to understand why its typed to itself MyNumber&lt;MyNumber&gt; boundNumber1, boundNumber2; void example() { // PROBLEM 3: There will be a compiler warning about the raw types. rawNumber1.approxEquals(rawNumber2); // Works without warnings, see PROBLEM 2 though. boundNumber1.approxEquals(boundNumber2); } } </code></pre>
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    1. COYou know, "not a real question" =/= "I don't understand the question".
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      1. USJUST MY correct OPINION
 

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