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    <p>I wasn't going to answer this question but there are two answers here (that are getting voted up!) that are just plain wrong. Consider these expressions:</p> <pre><code>String a = "a" + "b" + "c"; String b = System.getProperty("blah") + "b"; </code></pre> <p>The first is evaluated at <strong>compile-time</strong>. The second is evaluated at <strong>run-time</strong>.</p> <p>So <strong>never</strong> replace constant concatenations (of any type) with StringBuilder, StringBuffer or the like. Only use those where variables are invovled and generally only when you're appending a lot of operands or you're appending in a loop.</p> <p>If the characters are constant, this is fine:</p> <pre><code>String s = "" + 'a' + 'b' + 'c'; </code></pre> <p>If however they aren't, consider this:</p> <pre><code>String concat(char... chars) { if (chars.length == 0) { return ""; } StringBuilder s = new StringBuilder(chars.length); for (char c : chars) { s.append(c); } return s.toString(); } </code></pre> <p>as an appropriate solution.</p> <p>However some might be tempted to optimise:</p> <pre><code>String s = "Name: '" + name + "'"; // String name; </code></pre> <p>into this:</p> <pre><code>String s = new StringBuilder().append("Name: ").append(name).append("'").toString(); </code></pre> <p>While this is well-intentioned, the bottom line is <strong>DON'T</strong>.</p> <p>Why? As another answer correctly pointed out: the compiler does this for you. So in doing it yourself, you're not allowing the compiler to optimise the code or not depending if its a good idea, the code is harder to read and its unnecessarily complicated.</p> <p><strong>For low-level optimisation the compiler is better at optimising code than you are.</strong></p> <p>Let the compiler do its job. In this case the worst case scenario is that the compiler implicitly changes your code to exactly what you wrote. Concatenating 2-3 Strings might be more efficient than constructing a StringBuilder so it might be better to leave it as is. The compiler knows whats best in this regard.</p>
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    1. POHow to concatenate characters in java?
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    1. COindeed you are right. would be a bad design and silly if "a"+"b" created a stringbuilder. and i also agree that for only 1-5 concats, doing it with + is probably better than going into the hassle of creating a StringBuilder.
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      1. USJohannes Schaub - litb
    2. COThe compiler does that for you, but yes, in your last example, that is what the compiler outputs. I completely agree that you *shouldn't* do that yourself, but I do think it's important to understand what happens.
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    3. COI incorporated your suggestions into my answer.
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