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POGeneric Type From Enum & The Builder Pattern
 

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  1. POGeneric Type From Enum & The Builder Pattern
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    <p>I'm trying to create a builder pattern that uses generics to provide type checking on some of the methods. Currently I have the following working:</p> <pre><code>ParameterBuilder.start(String.class).setName("foo").setDefaultValue("Hello").build(); ParameterBuilder.start(Integer.class).setName(bar).setDefaultValue(42).build(); ParameterBuilder.start(Boolean.class).setName(bar).setDefaultValue(false).build(); </code></pre> <p>Using the code:</p> <pre><code>public class ParameterBuilder&lt;T&gt; { private String name; private T defaultValue; public static &lt;T2&gt; ParameterBuilder&lt;T2&gt; start(Class&lt;T2&gt; type) { return new ParameterBuilder&lt;T2&gt;(); } // Other methods excluded for example } </code></pre> <p>So the type of the input for the <code>setDefaultValue</code> method is defined by what's passed into the <code>start</code> method, just as I want.</p> <p>But now I want to extend what's being passed into <code>start()</code> to contain a little more information. Essentially I want to pass in a "type" for the parameters I creating. Sometimes these parameters will be things like "email", "url" etc. The default value will still be of a known type (String in those cases), so I'd like to have something like:</p> <pre><code>ParameterBuilder.start(EMAIL).setName("email").setDefaultValue("foo@bar.com").build(); ParameterBuilder.start(URL).setName("website").setDefaultValue("http://www.somewhere.com").build(); </code></pre> <p>Where at the moment EMAIL &amp; URL are enums, containing amongst other things - the class of the default value. But if I go down this route, how would I instantiate the parameter builder?</p> <pre><code>public static &lt;T2&gt; ParameterBuilder&lt;T2&gt; start(ParameterType paramType) { Class&lt;T2&gt; type = paramType.getTypeClass(); // How do I instantiate my ParameterBuilder with the right type? } </code></pre> <p>If it can't be done using enums (which I can see being the case), does anyone have a suggestion for a different solution?</p>
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    1. COCan you show what exactly is `EMAIL`, `URL`. Are they 2 different enums? Are they instances of two enums? What are they?
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      1. USRohit Jain
    2. COIn my case, I had a ParameterType echoing something like: `public enum ParameterType { STRING(String.class, "String"), INTEGER(Integer.class, "Integer"), MULTILINE(String.class, "Multine Text"), HTML(String.class, "HTML"), DATE(Date.class, "Date"), BOOLEAN(Boolean.class, "Boolean"); // Methods followed`
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