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copied!<p>No, they are NOT equivalent the way you expressed them.</p> <pre><code>short x = 0, y = 0; x -= y; // This compiles fine! x = x - y; // This doesn't compile!!! // "Type mismatch: cannot convert from int to short" </code></pre> <p>The problem with the third line is that <code>-</code> performs what is called "numeric promotion" (<a href="http://java.sun.com/docs/books/jls/third_edition/html/conversions.html#5.6" rel="nofollow noreferrer">JLS 5.6</a>) of the <code>short</code> operands, and results in an <code>int</code> value, which cannot simply be assigned to a <code>short</code> without a cast. <em>Compound assignment operators contain a hidden cast!</em></p> <p>The exact equivalence is laid out in <a href="http://java.sun.com/docs/books/jls/third_edition/html/expressions.html#15.26.2" rel="nofollow noreferrer">JLS 15.26.2 Compound Assignment Operators</a>:</p> <blockquote> <p>A compound assignment expression of the form <em>E1 op= E2</em> is equivalent to <em>E1 = (T)((E1) op (E2))</em>, where <em>T</em> is the type of <em>E1</em>, except that <em>E1</em> is evaluated only once.</p> </blockquote> <p>So to clarify some of the subtleties:</p> <ul> <li>Compound assignment expression doesn't reorder the operands <ul> <li>Left hand side stays on the left, right hand side stays on the right</li> </ul></li> <li>Both operands are fully-parenthesized to ensure <em>op</em> has the lowest precedence <ul> <li><code>int x = 5; x *= 2 + 1; // x == 15, not 11</code></li> </ul></li> <li>There is a hidden cast <ul> <li><code>int i = 0; i += 3.14159; // this compiles fine!</code></li> </ul></li> <li>The left hand side is only evaluated once <ul> <li><code>arr[i++] += 5; // this only increments i once</code></li> </ul></li> </ul> <p>Java also has <code>*=</code>, <code>/=</code>, <code>%=</code>, <code>+=</code>, <code>-=</code>, <code><<=</code>, <code>>>=</code>, <code>>>>=</code>, <code>&=</code>, <code>^=</code> and <code>|=</code>. The last 3 are also defined for booleans (<a href="http://java.sun.com/docs/books/jls/third_edition/html/expressions.html#15.22.2" rel="nofollow noreferrer">JLS 15.22.2 Boolean Logical Operators</a>).</p> <h3>Related questions</h3> <ul> <li><a href="https://stackoverflow.com/questions/2696812/varying-behavior-for-possible-loss-of-precision/">Varying behavior for possible loss of precision</a></li> <li><a href="https://stackoverflow.com/questions/2324549/why-doesnt-java-have-compound-assignment-versions-of-the-conditional-and-and-con">Why doesn’t Java have compound assignment versions of the conditional-and and conditional-or operators? (&&=, ||=)</a></li> </ul>

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