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    <blockquote> <p>I understand that it provides a getter to retrieve both x and y at once in a array instead of a separate getter for each, so the caller will see consistent value, but why private constructor ? what's the trick here?</p> </blockquote> <p>What we want here is chaining of constructor calls to avoid code duplication. Ideally something like this is what we want:</p> <pre><code>public SafePoint(SafePoint p) { int[] values = p.get(); this(values[0], values[1]); } </code></pre> <p>But that won't work because we will get a compiler error:</p> <pre><code>call to this must be first statement in constructor </code></pre> <p>And we can't use this either:</p> <pre><code>public SafePoint(SafePoint p) { this(p.get()[0], p.get()[1]); // alternatively this(p.x, p.y); } </code></pre> <p>Because then we have a condition where the values might have been changed between the call to <code>p.get()</code>.</p> <p>So we want to capture the values from SafePoint and chain to another constructor. That is why we will use the <em>private constructor capture idiom</em> and capture the values in a private constructor and chain to a "real" constructor:</p> <pre><code>private SafePoint(int[] a) { this(a[0], a[1]); } </code></pre> <p>Also note that</p> <pre><code>private SafePoint (int [] a) { this (a[0], a[1]); } </code></pre> <p>does not make any sense outside the class. A 2-D point has two values, not arbitrary values like the array suggests. It has no checks for the length of the array nor that it is not <code>null</code>. It is only used within the class and the caller knows it is safe to call with two values from the array.</p>
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    1. POPrivate constructor to avoid race condition
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    1. COThere's a bit more to it; if the constructor was made public, the class would no longer be thread-safe.
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    2. CO@biziclop Updated with thread-safeness
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