Function.Function of Java 8 with multiple parameters : <p>I read many examples about how to easily define a lambda in Java 8. This lambda takes always one parameter like <code>f1</code>:</p>

<pre><code>Function&lt;Integer,Integer&gt; f1 = (x) -&gt; Math.pow(x,2);
</code></pre>

<p>Of course, you can extend the body like <code>f2</code>: </p>

<pre><code>Function&lt;Integer,Integer&gt; f2 = (x) -&gt; {if (x &lt; 0)  return 0;
                                       else return Math.pow(x,2);};
</code></pre>

<p>But I cannot find a way to define a lambda with a variable number of paramters like <code>f3</code>:</p>

<pre><code>Function&lt;Integer,Integer,Integer&gt; f3 = (x,y) -&gt; {return x + y};
</code></pre>

<p>or without parameter like <code>f4</code>:</p>

<pre><code>Function&lt;Double&gt; f4 = () -&gt; {return Math.random()};
</code></pre>

<p>I am almost sure that you can define own functional interface (i.e., create a new file commonly) to develop <code>f3</code> and <code>f4</code>, but Is there some way to easily define them? </p>
