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This article mainly shows you "what are the string concatenation ways in Java code", the content is simple and clear, and I hope it can help you solve your doubts. Let me lead you to study and learn what string concatenation methods are in Java code.

Analyze process environment

System: windows 10 21H1

JDK: OpenJDK 1.8.0_302

Sample code for analysis: @ Slf4jpublic class StringConcat {@ SneakyThrows public static void main (String [] args) {log.info ("java virtual machine warm-up starts"); String [] strs = new String [6000000]; for (int I = 0; I < strs.length; iTunes +) {strs [I] = id ();} loopStringJoiner (strs); loopStringJoin (strs) LoopStringBuilder (strs); log.info ("java virtual machine warm-up ends"); Thread.sleep (1000); log.info ("start testing:"); 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; id +) {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; iTunes +) {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; iTunes +) {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 ();}

Results and summary

-java virtual machine warm-up starts

-java virtual machine warm-up ends

-start testing:

-loop-plus: execution timeout

-loop-stringBuilderCapacity: 285

-loop-stringBuilder: 1968

-loop-String.join: 1313

-loop-stringJoiner: 1238

-simple-Plus: 812

-simple-StringBuilder: 840

-simple-StringBuffer: 857

After many tests, it can be found that in the scenario of string cyclic stitching, the performance of using "+" sign directly is the lowest, and the performance of StringBuilder with initial capacity is the highest, and the performance of other methods is not much different.

After many tests, it can be found that in the scenario of simple string stitching, the performance gap between the use of "+" sign, StringBuilder and StringBuffer is about 5%, which can be understood as testing error, and the performance of the three methods can be considered consistent.

Code and result analysis

1. Comparison between StringBuilder and StringBuffer

In the scenario where there is no competition for shared resources, JVM will use methods such as biased locks to optimize or even eliminate locks. There is no significant difference in performance between using Synchronized keywords or not.

two。 Bytecode analysis

Comparing the bytecode of the above two methods # simplePlus and # simpleStringBuilder, it is obvious that the execution content of the two methods is basically the same, but the processing flow is shorter when using the "+" sign directly, which shows that the compiler has made a deep optimization, and the optimized bytecode will theoretically have higher performance:

/ / 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 125L0 NEW java/lang/StringBuilder DUP INVOKESPECIAL java/lang/StringBuilder. () 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 L12 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. () V ASTORE 3 L1 LINENUMBER 130L1 ALOAD 3 ALOAD 0 INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;) Ljava/lang/StringBuilder; POP L2 LINENUMBER 131L2 ALOAD 3 LDC "+" INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;) Ljava/lang/StringBuilder; POP L3 LINENUMBER 132L3 ALOAD 3 ALOAD 1 INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;) Ljava/lang/StringBuilder POP L4 LINENUMBER 133L4 ALOAD 3 LDC "+" INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;) Ljava/lang/StringBuilder; POP L5 LINENUMBER 134L5 ALOAD 3 ALOAD 2 INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;) Ljava/lang/StringBuilder; POP L6 LINENUMBER 135L6 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 are all the contents of the article "what are the string concatenation methods in Java code". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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