Java multiline string formation

Question

I'm by no means a java programmer, so this may seem pretty basic.

Which of these are 'better' when you want to keep your code lines short.

String str = "First part of a string.";
str += " Second part of string.";

or

String str = "First part of string." +
" Second part of string."

I guess my question is do both the += and + make a new String object? If they do then neither really are better, it would just be a matter of preference. The example I gave would be a good example of real world use. I don't want a comparison of doing a concatenation 3 times to 1000 times with either method.

Thanks

I can't speak for the actual implementation, but it seems to me like the second one would make it pretty easy to optimize the concatenation away, and just consider both parts of the string a single literal. — jpm
– jpm, Commented Apr 13, 2012 at 16:16
Awesome guys, thanks! I'm a ruby developer and using << to concat two strings doesn't create a new object, just modifies the one you added to. So I was wondering how Java handled the similar problem. — Luke
– Luke, Commented Apr 13, 2012 at 16:23
For general string building (when you need to concatenate lots of strings), StringBuilder is a great tool to help avoid the expenses of raw concatenation. — jpm
– jpm, Commented Apr 13, 2012 at 16:24

Tony Ennis · Accepted Answer · 2012-04-13 16:16:33Z

3

I prefer the 2nd method. The reason is that the compiler will likely combine the result of the concatenation into a single string at compile time while the 1st method may be done at run-time (depending on the actual implemention.) It's a small thing unless you're doing something millions of times, however.

answered Apr 13, 2012 at 16:16

Tony Ennis

12.4k8 gold badges59 silver badges78 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

user207421 Over a year ago

Will definitely combine the result of the concatenation at compile time. This is required behaviour.

Roger Lindsjö · Accepted Answer · 2018-02-14 18:33:55Z

2

The Java compiler is actually required to concatenate the second example at compile time. See 15.28. Constant Expressions and 3.10.5. String Literals.

edited Feb 14, 2018 at 18:33

answered Apr 13, 2012 at 16:23

Roger Lindsjö

11.6k1 gold badge46 silver badges56 bronze badges

1 Comment

user207421 Over a year ago

The compiler is required to concatenate it at compile time. Nothing to do with the JVM yet.

josh.trow · Accepted Answer · 2012-04-13 16:18:19Z

0

Here's what I get when I compile then decompile this:

public static void main(String[] args) {
    String str = "First";
    str += " Second";
    System.out.println(str);

    String str2 = "First" + " Second";
    System.out.println(str2);
}

Becomes:

public static void main(String args[]) {
    String s = "First";
    s = (new StringBuilder()).append(s).append(" Second").toString();
    System.out.println(s);
    String s1 = "First Second";
    System.out.println(s1);
}

So the second method is better.

answered Apr 13, 2012 at 16:18

josh.trow

4,90123 silver badges31 bronze badges

Comments

ChadNC · Accepted Answer · 2012-04-13 16:27:43Z

0

StringBuilder sb = new StringBuilder();
sb.append("First part");
sb.append("Second part");
System.out.print(sb.toString());

answered Apr 13, 2012 at 16:27

ChadNC

2,5034 gold badges25 silver badges40 bronze badges

Comments

bradylange · Accepted Answer · 2019-04-21 17:55:13Z

0

Following Java's coding conventions:

String str = "First part of string. "
             + "Second part of string.";

Make sure the '+' operator begins the next line this improves readability. Using this style allows for readable and efficient code. https://www.oracle.com/technetwork/java/javase/documentation/codeconventions-136091.html#248

Hope this helps!

Happy coding,

Brady

answered Apr 21, 2019 at 17:55

bradylange

3945 silver badges6 bronze badges

Collectives™ on Stack Overflow

Java multiline string formation

5 Answers 5

1 Comment

1 Comment

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

1 Comment

1 Comment

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related