java中字符串常量的连接 [英] concatenation of string constants in java
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问题描述
In C++, the best canonical way to create a multiline string of which I am aware is to create adjacent strings and let the compiler concatenate them at compile time, like this:
string s = "This is a very long string ...
"
" and it keeps on going...";
In Java, the only way I know to do this is with concatenation:
String s = "This is a very long string ...
" +
" and it keeps on going...";
The question is, does this generate a single string at runtime, or does java actually concatenate at compile time also? The reason the question comes up is because of the following behavior:
String s1 = "abc";
String s2 = "abc";
System.out.println(s1 == s2); // this prints true, because the compiler
// generates only one "abc" object
String s3 = "a";
s3 += "bc";
System.out.println(s1 == s3); // false
解决方案
String s3 = "a";
s3 += "bc";
Is same as:
String s3 = "a";
s3 = new StringBuilder().append(s3).append("bc").toString();
So it creates a new instance of String
.
You can even try:
String s = null;
s += null;
System.out.println(s); // prints "nullnull"
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