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  1. PO
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    <h1><code>+</code> operator</h1> <pre><code>String s = s1 + s2 </code></pre> <p>Behind the scenes this is translated to:</p> <pre><code>String s = new StringBuilder(s1).append(s2).toString(); </code></pre> <p>Imagine how much extra work it adds if you have <code>s1 + s2</code> here:</p> <pre><code>stringBuilder.append(s1 + s2) </code></pre> <p>instead of:</p> <pre><code>stringBuilder.append(s1).append(s2) </code></pre> <h2>Multiple strings with <code>+</code></h2> <p>Worth to note that:</p> <pre><code>String s = s1 + s2 + s3 + ... +sN </code></pre> <p>is translated to:</p> <pre><code>String s = new StringBuilder(s1).append(s2).append(s3)...apend(sN).toString(); </code></pre> <h1><code>concat()</code></h1> <pre><code>String s = s1.concat(s2); </code></pre> <p><code>String</code> creates <code>char[]</code> array that can fit both <code>s1</code> and <code>s2</code>. Copies <code>s1</code> and <code>s2</code> contents to this new array. Actually requires less work then <code>+</code> operator.</p> <h1><code>StringBuilder.append()</code></h1> <p>Maintains an internal <code>char[]</code> array that grows when needed. No extra <code>char[]</code> is created if the internal one is sufficiently big.</p> <pre><code>stringBuilder.append(s1.concat(s2)) </code></pre> <p>is also performing poorly because <code>s1.concat(s2)</code> creates an extra <code>char[]</code> array and copies <code>s1</code> and <code>s2</code> to it just to copy that new array contents to internal <code>StringBuilder</code> <code>char[]</code>.</p> <p>That being said you should use <code>append()</code> all the time and append raw strings (your first code snippet is correct).</p>
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    1. USTomasz Nurkiewicz
    1. USTomasz Nurkiewicz
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    1. COThanks for your help, and the in-depth explanation; that's what I really needed.
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      1. USNick Rolando
    2. COAlthough newer versions of the compiler automatically optimize the + operator to a string builder it isn't necessarily a good thing to assume it will as older versions don't. There is a very important topic that is being ignored in this whole discussion which is actually one of the main purposes for StringBuilder which is the string pool. Using a string builder keeps everything as a char[] and doesn't create an intermediate String like the + operator did before compiler optimizations(used to just do a concat). Using concat creates an intermediate String object which is cached but not used.
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      1. USLINEMAN78
    3. COSo if I'm doing a *one-time statement* (not multiple statements accross a method) concatenation on several different strings. It would be okay to use `+` on the String objects instead of creating a `StringBuilder` for this one time concatenation, since it will basically do the same thing?
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