Java 编译器是否包含字符串常量折叠?

Does Java Compiler include String Constant Folding?(Java 编译器是否包含字符串常量折叠?)

问题描述

我发现 Java 支持原始类型的常量折叠，但是 Strings 呢?

I found out that Java supports constant folding of primitive types, but what about Strings?

示例

如果我创建以下源代码

out.write(""
        + "<markup>"
        + "<nested>"
        + "Easier to read if it is split into multiple lines"
        + "</nested>"
        + "</markup>"
        + "");

编译后的代码中有什么内容?

What goes into the compiled code?

组合版本?out.write("<markup><nested>如果分成多行更容易阅读</nested></markup>");

还是效率较低的运行时串联版本?out.write(new StringBuilder("").append("<markup>").append("<nested>").append("拆分成多行更容易阅读").append("</nested>").append("</markup>").append(""));

Or the less efficient run-time concatenation version? out.write(new StringBuilder("").append("<markup>").append("<nested>").append("Easier to read if it is split into multiple lines").append("</nested>").append("</markup>").append(""));

推荐答案

这是一个简单的测试:

public static void main(final String[] args) {
    final String a = "1" + "2";
    final String b = "12";        

    System.out.println(a == b);
}

输出:

true

所以，是的，编译器会折叠.

So, yes, the compiler will fold.

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