加号被转换为StringBuilder。除非两个字符串都是常量，以便编译器可以在编译时将它们组合在一起。至少，Sun的编译器是这样的，我怀疑大多数(如果不是所有)其他编译器也会这样做。

So:

String a="Hello";
String b="Goodbye";
String c=a+b;

通常生成完全相同的代码:

String a="Hello";
String b="Goodbye":
StringBuilder temp=new StringBuilder();
temp.append(a).append(b);
String c=temp.toString();

另一方面:

String c="Hello"+"Goodbye";

等于:

String c="HelloGoodbye";

也就是说，为了可读性，在多行中使用加号将字符串字面量分开并不会受到惩罚。

由于Java(还)不支持多行字符串，目前唯一的方法是使用前面提到的技术之一来破解它。我使用上面提到的一些技巧构建了下面的Python脚本:

import sys
import string
import os

print 'new String('
for line in sys.stdin:
    one = string.replace(line, '"', '\\"').rstrip(os.linesep)
    print '  + "' + one + ' "'
print ')'

把它放在一个名为javastringify.py的文件中，把你的字符串放在一个名为mystring.txt的文件中，然后像下面这样运行:

cat mystring.txt | python javastringify.py

然后，您可以复制输出并将其粘贴到编辑器中。

修改这需要处理任何特殊情况，但这是为我的需要。希望这能有所帮助!

当我读到多行语法确实是为jdk7计划的(在java存在了多少年之后?)时，我有点恼火。有趣的是，甚至还没有readAll()函数用于读取文件的完整内容(仅从jdk7读取，啊啊)，因此下面的代码读取单行。

/*
  MakeMultiline v1.0 (2010) - Free to use and copy.

  Small gadget to turn text blobs into one java string literal
  (doing the split in lines, adding \n at each end and enclosing
  in double quotes). Does escape quotes encountered in the text blob.

  Useful for working around missing multiline string syntax in java
  prior jdk7. Use with:

     java MakeMultiline "    "
  or
     java MakeMultiline "    " mytextfile.txt
*/

import java.io.*;

class MakeMultiline {
  public static void main(String[] args) {
    try {
      // args[0]: indent
      // args[1]: filename to read (optional; stdin if not given)
      // Beware the nmb of newlines at the end when using stdin!

      String indent = (args.length > 0 ? args[0] : "");
      FileReader fr = null; BufferedReader br;
      if (args.length > 1)
        { fr =  new FileReader(args[1]); br = new BufferedReader(fr); }
      else
        { br = new BufferedReader(new InputStreamReader(System.in)); }
      String s; String res = "";
      while((s = br.readLine()) != null) {
        if (res.length() > 0) res += " +\n";
        res += indent + "\"" + s.replace("\"", "\\\"") + "\\n\"";
      }
      br.close(); if (fr != null) fr.close();
      System.out.println(res + ";");
    }
    catch(Exception e) {
      System.out.println("Exception: " + e);
    }
  }
}

这对我来说是最快的解决办法。(2010-01-27)

Java 13预览:

Text Blocks Come to Java. Java 13 delivers long-awaited multiline string by Mala Gupta With text blocks, Java 13 is making it easier for you to work with multiline string literals. You no longer need to escape the special characters in string literals or use concatenation operators for values that span multiple lines. Text block is defined using three double quotes (""") as the opening and closing delimiters. The opening delimiter can be followed by zero or more white spaces and a line terminator.

例子:

 String s1 = """
 text
 text
 text
 """;

我还没有看到的另一个答案是java.io.PrintWriter。

StringWriter stringWriter = new StringWriter();
PrintWriter writer = new PrintWriter(stringWriter);
writer.println("It was the best of times, it was the worst of times");
writer.println("it was the age of wisdom, it was the age of foolishness,");
writer.println("it was the epoch of belief, it was the epoch of incredulity,");
writer.println("it was the season of Light, it was the season of Darkness,");
writer.println("it was the spring of hope, it was the winter of despair,");
writer.println("we had everything before us, we had nothing before us");
String string = stringWriter.toString();

此外，java.io.BufferedWriter有一个newLine()方法的事实也未被提及。

使用Properties.loadFromXML (InputStream)。不需要外部库。

比起混乱的代码(因为可维护性和设计是您所关心的)，最好不要使用长字符串。 从读取xml属性开始:

 InputStream fileIS = YourClass.class.getResourceAsStream("MultiLine.xml");
 Properties prop = new Properies();
 prop.loadFromXML(fileIS);

然后，您可以使用您的多行字符串在一个更可维护的方式…

static final String UNIQUE_MEANINGFUL_KEY = "Super Duper UNIQUE Key";
prop.getProperty(UNIQUE_MEANINGFUL_KEY) // "\n    MEGA\n   LONG\n..."

MultiLine.xml`位于同一个文件夹YourClass:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd">

<properties>
    <entry key="Super Duper UNIQUE Key">
       MEGA
       LONG
       MULTILINE
    </entry>
</properties>

注:你可以使用<![CDATA[”…"]]>为类似xml的字符串。