关于java中字符串连接使用 Stirng+String+... 效率的一点想法
记得自己还是个连菜鸟都算不上的coder的时候，老鸟们总教育我：代码里不要出现String+String+...这种代码，非多线程的情况下要用StringBuilder效率才高
当时没啥感觉，最近闲来无事，想看看java编译器都对String+String+...这种代码怎么处理的呢？于是发现javac也是用StringBuilder来处理的，所以我感觉这两者效率上是没有区别的，如本人理解有错，望老鸟给予指正...
请看代码吧，主要代码我都加上了注释
D:\Workspace\MyEclipse\workspace\Test\bin\test>javap Test -verboseCompiled from "Test.java"public class test.Test extends java.lang.Object SourceFile: "Test.java" minor version: 0 major version: 50 Constant pool:const #1 = class #2; // test/Testconst #2 = Asciz test/Test;const #3 = class #4; // java/lang/Objectconst #4 = Asciz java/lang/Object;const #5 = Asciz <init>;const #6 = Asciz ()V;const #7 = Asciz Code;const #8 = Method #3.#9; // java/lang/Object."<init>":()Vconst #9 = NameAndType #5:#6;// "<init>":()Vconst #10 = Asciz LineNumberTable;const #11 = Asciz LocalVariableTable;const #12 = Asciz this;const #13 = Asciz Ltest/Test;;const #14 = Asciz main;const #15 = Asciz ([Ljava/lang/String;)V;const #16 = class #17; // java/lang/Stringconst #17 = Asciz java/lang/String;const #18 = String #19; // 小菜鸟const #19 = Asciz 小菜鸟;const #20 = Method #16.#21; // java/lang/String."<init>":(Ljava/lang/String;)Vconst #21 = NameAndType #5:#22;// "<init>":(Ljava/lang/String;)Vconst #22 = Asciz (Ljava/lang/String;)V;const #23 = String #24; // 大菜鸟const #24 = Asciz 大菜鸟;const #25 = class #26; // java/lang/StringBuilderconst #26 = Asciz java/lang/StringBuilder;const #27 = Method #16.#28; // java/lang/String.valueOf:(Ljava/lang/Object;)Ljava/lang/String;const #28 = NameAndType #29:#30;// valueOf:(Ljava/lang/Object;)Ljava/lang/String;const #29 = Asciz valueOf;const #30 = Asciz (Ljava/lang/Object;)Ljava/lang/String;;const #31 = Method #25.#21; // java/lang/StringBuilder."<init>":(Ljava/lang/String;)Vconst #32 = Method #25.#33; // java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;const #33 = NameAndType #34:#35;// append:(Ljava/lang/String;)Ljava/lang/StringBuilder;const #34 = Asciz append;const #35 = Asciz (Ljava/lang/String;)Ljava/lang/StringBuilder;;const #36 = String #37; // 老鸟const #37 = Asciz 老鸟;const #38 = Method #25.#39; // java/lang/StringBuilder.toString:()Ljava/lang/String;const #39 = NameAndType #40:#41;// toString:()Ljava/lang/String;const #40 = Asciz toString;const #41 = Asciz ()Ljava/lang/String;;const #42 = Asciz args;const #43 = Asciz [Ljava/lang/String;;const #44 = Asciz s1;const #45 = Asciz Ljava/lang/String;;const #46 = Asciz s2;const #47 = Asciz resultString;const #48 = Asciz SourceFile;const #49 = Asciz Test.java;{public test.Test(); Code: Stack=1, Locals=1, Args_size=1 0: aload_0 1: invokespecial #8; //Method java/lang/Object."<init>":()V 4: return LineNumberTable: line 3: 0 LocalVariableTable: Start Length Slot Name Signature 0 5 0 this Ltest/Test;public static void main(java.lang.String[]); Code: Stack=3, Locals=4, Args_size=1 0: new #16; //class java/lang/String |我加上的：创建一个新对象，对象类型存储在常量池#16 3: dup//我加上的：复制栈顶部一个字长的内容 4: ldc #18; //String 小菜鸟 |我加上的：把常量池中索引为#18的值压入栈 6: invokespecial #20; //Method java/lang/String."<init>":(Ljava/lang/String;)V |我加上的：调用初始化方法 9: astore_1//我加上的：将引用类型存入局部变量1 10: new #16; //class java/lang/String |我加上的：10-19同上实例化另一个String对象(大菜鸟) 13: dup 14: ldc #23; //String 大菜鸟 16: invokespecial #20; //Method java/lang/String."<init>":(Ljava/lang/String;)V 19: astore_2 20: new #25; //class java/lang/StringBuilder |我加上的：创建一个StringBuilder对象 23: dup 24: aload_1//我加上的：从局部变量1中装载引用类型 25: invokestatic #27; //Method java/lang/String.valueOf:(Ljava/lang/Object;)Ljava/lang/String; 28: invokespecial #31; //Method java/lang/StringBuilder."<init>":(Ljava/lang/String;)V 31: aload_2//我加上的：从局部变量2中装载引用类型 //哈哈，看到这里了吧，javac(我的jdk版本是1.6)编译后的字节码对于String+String+...的处理也是使用StringBuilder的append的 32: invokevirtual #32; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder; 35: ldc #36; //String 老鸟 //同理，连接字符串“老鸟” 37: invokevirtual #32; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder; 40: invokevirtual #38; //Method java/lang/StringBuilder.toString:()Ljava/lang/String; 43: astore_3 44: return LineNumberTable: line 7: 0 line 8: 10 line 10: 20 line 11: 44 LocalVariableTable: Start Length Slot Name Signature 0 45 0 args [Ljava/lang/String; 10 35 1 s1 Ljava/lang/String; 20 25 2 s2 Ljava/lang/String; 44 1 3 resultString Ljava/lang/String;}D:\Workspace\MyEclipse\workspace\Test\bin\test>