前言：
现在你们对“java中的字符串拼接”可能比较注重，看官们都想要了解一些“java中的字符串拼接”的相关内容。那么小编同时在网络上网罗了一些有关“java中的字符串拼接””的相关资讯，希望小伙伴们能喜欢，各位老铁们一起来学习一下吧！本文研讨的字符串拼接方式为以下4种：“+”号、StringBuilder、StringJoiner、String#join，对比分析及探讨最佳实践。
结论
后面内容比较枯燥，所以先说结论：
本文研讨的字符串拼接方式为以下4种：“+”号、StringBuilder、StringJoiner、String#join在简单的字符串拼接场景中「如："a" + "b" + "c"」，以上四种方式性能无明显差异。在循环字符串拼接的场景下，使用“+”号性能最低，其他三种方式性能也无明显差异，但是根据验证结果可粗浅发现，指定初始容量的StringBuilder效率最高。当然不光考虑性能，也要考虑垃圾回收效率的问题，避免OOM。本文最后补充对比了StringBuffer，在无争抢共享资源的场景下，StringBuffer性能并未明显变差。最佳实践阿里巴巴Java开发手册-日志规约「5」可进行优化：使用占位符的形式可读性、便捷性不佳，可考虑使用Lambda，延迟字符串的拼接，且使用更加便利。阿里巴巴Java开发手册-OOP 规约「23」可进行优化：循环拼接时须使用StringBuilder；在拼接大量的大容量字符串时，使用StringBuilder尽量指定初始容量。简单的字符串拼接可用任意方式，推荐直接使用“+”号拼接，可读性最优。尽量使用JDK等直接提供的特性「如“+”号拼接字符串，Synchronized关键词等」，因为编译器+JVM会持续对此进行优化，JDK升级即可获得更大的收益。除非有明确的理由可以自行实现类似的功能。在需要考虑线程安全的场景可以考虑使用StringBuffer进行字符串拼接，不过一般来说没有这种需求，故不应该使用StringBuffer，避免增加复杂性。分析过程环境系统: windows 10 21H1JDK: OpenJDK 1.8.0_302分析用示例代码：
@Slf4jpublic class StringConcat { @SneakyThrows public static void main(String[] args) { log.info("java虚拟机预热开始"); String[] strs = new String[6000000]; for (int i = 0; i < strs.length; i++) { strs[i] = id(); } loopStringJoiner(strs); loopStringJoin(strs); loopStringBuilder(strs); log.info("java虚拟机预热结束"); Thread.sleep(1000); log.info("开始测试："); Thread.sleep(1000); Stopwatch stopwatchLoopPlus = Stopwatch.createStarted();// loopPlus(strs); log.info("loop-plus: " + stopwatchLoopPlus.elapsed(TimeUnit.MILLISECONDS)); Thread.sleep(1000); Stopwatch stopwatchLoopStringBuilderCapacity = Stopwatch.createStarted(); loopStringBuilderCapacity(strs); log.info("loop-stringBuilderCapacity: " + stopwatchLoopStringBuilderCapacity.elapsed(TimeUnit.MILLISECONDS)); Thread.sleep(1000); Stopwatch stopwatchLoopStringBuilder = Stopwatch.createStarted(); loopStringBuilder(strs); log.info("loop-stringBuilder: " + stopwatchLoopStringBuilder.elapsed(TimeUnit.MILLISECONDS)); Thread.sleep(1000); Stopwatch stopwatchLoopJoin = Stopwatch.createStarted(); loopStringJoin(strs); log.info("loop-String.join: " + stopwatchLoopJoin.elapsed(TimeUnit.MILLISECONDS)); Thread.sleep(1000); Stopwatch stopwatchLoopStringJoiner = Stopwatch.createStarted(); loopStringJoiner(strs); log.info("loop-stringJoiner: " + stopwatchLoopStringJoiner.elapsed(TimeUnit.MILLISECONDS)); Thread.sleep(1000); Stopwatch stopwatchSimplePlus = Stopwatch.createStarted(); for (int i = 0; i < 500000; i++) { simplePlus(id(), id(), id()); } log.info("simple-Plus: " + stopwatchSimplePlus.elapsed(TimeUnit.MILLISECONDS)); Thread.sleep(1000); Stopwatch stopwatchSimpleStringBuilder = Stopwatch.createStarted(); for (int i = 0; i < 500000; i++) { simpleStringBuilder(id(), id(), id()); } log.info("simple-StringBuilder: " + stopwatchSimpleStringBuilder.elapsed(TimeUnit.MILLISECONDS)); Thread.sleep(1000); Stopwatch stopwatchSimpleStringBuffer = Stopwatch.createStarted(); for (int i = 0; i < 500000; i++) { simpleStringBuffer(id(), id(), id()); } log.info("simple-StringBuffer: " + stopwatchSimpleStringBuffer.elapsed(TimeUnit.MILLISECONDS)); } private static String loopPlus(String[] strs) { String str = ""; for (String s : strs) { str = str + "+" + s; } return str; } private static String loopStringBuilder(String[] strs) { StringBuilder str = new StringBuilder(); for (String s : strs) { str.append("+"); str.append(s); } return str.toString(); } private static String loopStringBuilderCapacity(String[] strs) { StringBuilder str = new StringBuilder(strs[0].length() * strs.length); for (String s : strs) { str.append("+"); str.append(s); } return str.toString(); } private static String loopStringJoin(String[] strs) { StringJoiner joiner = new StringJoiner("+"); for (String str : strs) { joiner.add(str); } return joiner.toString(); } private static String loopStringJoiner(String[] strs) { return String.join("+", strs); } private static String simplePlus(String a, String b, String c) { return a + "+" + b + "+" + c; } private static String simpleStringBuilder(String a, String b, String c) { StringBuilder builder = new StringBuilder(); builder.append(a); builder.append("+"); builder.append(b); builder.append("+"); builder.append(c); return builder.toString(); } private static String simpleStringBuffer(String a, String b, String c) { StringBuffer buffer = new StringBuffer(); buffer.append(a); buffer.append("+"); buffer.append(b); buffer.append("+"); buffer.append(c); return buffer.toString(); } private static String id() { return UUID.randomUUID().toString(); }}结果及总结- java虚拟机预热开始- java虚拟机预热结束- 开始测试：- loop-plus: 执行超时- loop-stringBuilderCapacity: 285- loop-stringBuilder: 1968- loop-String.join: 1313- loop-stringJoiner: 1238- simple-Plus: 812- simple-StringBuilder: 840- simple-StringBuffer: 857复制代码多次测试，可发现在字符串循环拼接场景下，直接使用“+”号性能最低，有初始容量的StringBuilder性能最高，其他方式性能均没有太大差异。多次测试，可发现在字符串简单拼接场景下，使用“+”号、StringBuilder、StringBuffer性能差距在5%左右，可理解为测试误差，可认为三种方式性能一致。代码及结果分析1. StringBuilder与StringBuffer对比
在无争抢共享资源的场景下，JVM会使用偏向锁等方法优化，甚至会进行锁消除，使用Synchronized关键词与否，性能并无明显差异。
2. 字节码分析
对比上述#simplePlus和#simpleStringBuilder两个方法的字节码，可明显看到两方法执行内容基本一致，但是直接使用"+"号时处理流程更短，可见编译器进行了深度优化，使用优化后的字节码理论上会有更高的性能：
// access flags 0xA private static simplePlus(Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;)Ljava/lang/String; // parameter a // parameter b // parameter c L0 LINENUMBER 125 L0 NEW java/lang/StringBuilder DUP INVOKESPECIAL java/lang/StringBuilder.<init> ()V ALOAD 0 INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder; LDC "+" INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder; ALOAD 1 INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder; LDC "+" INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder; ALOAD 2 INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder; INVOKEVIRTUAL java/lang/StringBuilder.toString ()Ljava/lang/String; ARETURN L1 LOCALVARIABLE a Ljava/lang/String; L0 L1 0 LOCALVARIABLE b Ljava/lang/String; L0 L1 1 LOCALVARIABLE c Ljava/lang/String; L0 L1 2 MAXSTACK = 2 MAXLOCALS = 3 // access flags 0xA private static simpleStringBuilder(Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;)Ljava/lang/String; // parameter a // parameter b // parameter c L0 LINENUMBER 129 L0 NEW java/lang/StringBuilder DUP INVOKESPECIAL java/lang/StringBuilder.<init> ()V ASTORE 3 L1 LINENUMBER 130 L1 ALOAD 3 ALOAD 0 INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder; POP L2 LINENUMBER 131 L2 ALOAD 3 LDC "+" INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder; POP L3 LINENUMBER 132 L3 ALOAD 3 ALOAD 1 INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder; POP L4 LINENUMBER 133 L4 ALOAD 3 LDC "+" INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder; POP L5 LINENUMBER 134 L5 ALOAD 3 ALOAD 2 INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder; POP L6 LINENUMBER 135 L6 ALOAD 3 INVOKEVIRTUAL java/lang/StringBuilder.toString ()Ljava/lang/String; ARETURN L7 LOCALVARIABLE a Ljava/lang/String; L0 L7 0 LOCALVARIABLE b Ljava/lang/String; L0 L7 1 LOCALVARIABLE c Ljava/lang/String; L0 L7 2 LOCALVARIABLE builder Ljava/lang/StringBuilder; L1 L7 3 MAXSTACK = 2 MAXLOCALS = 4
作者：雪中亮
链接：
版权声明：
本站文章均来自互联网搜集，如有侵犯您的权益，请联系我们删除，谢谢。
标签： #java中的字符串拼接
