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copied!<p><strong>C++</strong></p> <p>There is a difference between </p> <pre><code>ClassType t(initialization arguments); </code></pre> <p>and </p> <pre><code>ClassType * pt; </code></pre> <p>The latter doesn't need to be initialized (set to NULL). The former does. Think of it as an integer. You can't have an int without a value, <strong>BUT</strong> you can have an int pointer without a value.</p> <p>So when you have:</p> <pre><code>class ClassType { OtherClass value; OtherClass * reference; }; </code></pre> <p>Then the declaration:</p> <pre><code>ClassType object; </code></pre> <p>automatically creates an instance of <code>OtherClass</code> in <code>value</code>. Therefore, if <code>OtherClass</code> has initialization, it must be done in the <code>ClassType</code> constructor. However, <code>reference</code> is just a pointer (address in memory) and can remain uninitialized. If you want an instance of <code>OtherClass</code> you must use</p> <pre><code>object.reference = new OtherClass(initialization arguments); </code></pre> <p><strong>Java</strong></p> <p>There is only </p> <pre><code>class ClassType { OtherClass reference; } </code></pre> <p>This is equivalent to a pointer in C++. In this case when you do:</p> <pre><code>ClassType object = new ClassType(); </code></pre> <p>You don't automatically create an instance of <code>OtherClass</code>. Therefore, you don't have to initialize anything in the constructor unless you want to. When you want an object of <code>OtherClass</code> you can use</p> <pre><code>object.reference = new OtherClass(); </code></pre>

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