字符串valueOf vs与空字符串连接 [英] String valueOf vs concatenation with empty string

问题描述

我正在从事Java代码优化工作。我不清楚 String.valueOf 或 +符号之间的区别：

I am working in Java code optimization. I'm unclear about the difference between String.valueOf or the +"" sign:

int intVar = 1;
String strVar = intVar + "";
String strVar = String.valueOf(intVar);

第2行和第3行有什么区别？

What is the difference between line 2 and 3?

推荐答案

public void foo(){
int intVar = 5;
String strVar = intVar+"";    
}

此方法使用StringBuilder创建结果字符串

This approach uses StringBuilder to create resultant String

public void foo();
  Code:
   0:   iconst_5
   1:   istore_1
   2:   new     #2; //class java/lang/StringBuilder
   5:   dup
   6:   invokespecial   #3; //Method java/lang/StringBuilder."<init>":()V
   9:   iload_1
   10:  invokevirtual   #4; //Method java/lang/StringBuilder.append:(I)Ljava/lan
g/StringBuilder;
   13:  ldc     #5; //String
   15:  invokevirtual   #6; //Method java/lang/StringBuilder.append:(Ljava/lang/
String;)Ljava/lang/StringBuilder;
   18:  invokevirtual   #7; //Method java/lang/StringBuilder.toString:()Ljava/la
ng/String;
   21:  astore_2
   22:  return

---

---

public void bar(){
int intVar = 5;
String strVar = String.valueOf(intVar);
}

这种方法只调用 String <的静态方法/ code>获取int的String版本

This approach invokes simply a static method of String to get the String version of int

public void bar();
  Code:
   0:   iconst_5
   1:   istore_1
   2:   iload_1
   3:   invokestatic    #8; //Method java/lang/String.valueOf:(I)Ljava/lang/Stri
ng;
   6:   astore_2
   7:   return

反过来调用 Integer.toString（）

which in turn calls Integer.toString()

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