How to concatenate a String in Java without using a complex code structure?

Question

I have the following java code:

String strTest = null;

for (AlternativeEntity alternativeEntity : msg.Guidance()
      .getAlternatives()) {

    strTest = strTest + alternativeEntity.getArrivalStation().getName() + ", ";

}

The output looks like this:

nullabc, xyz, oop,

How can I solve this problem and very bad character format? It would be great if I can create output like this:

abc, xyz, oop

You could use a library like Guava. See http://stackoverflow.com/questions/1751844/java-convert-liststring-to-a-joind-string — Denys Séguret, Oct 10 '13 at 11:51

Masudul · Answer 1 · 2013-10-10T11:57:30.187

3

Initialize strTest as:

String strTest = "";

Also, remove the last comma ,

strTest=strTest.substring(0, strTest.length()-1);

edited Oct 10 '13 at 11:57

answered Oct 10 '13 at 11:51

Masudul

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Or use Guava, which can do all the stuff for you in a single line. :) – Konstantin Yovkov Oct 10 '13 at 11:58

Konstantin Yovkov · Answer 2 · 2013-10-10T12:01:17.270

3

You can use Guava's Joiner#join(Iterable parts). For example:

Joiner joiner = Joiner.on(", ").skipNulls();
String result = joiner.join(list);
System.out.println(result);

Here, all the elements of the list will be printed comma separated without any trailing commas. Also, all the null elements will be skipped.

More info:

Strings Explained

edited Oct 10 '13 at 12:01

answered Oct 10 '13 at 11:52

Konstantin Yovkov

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That's what I wanted to answer. +1 – Adam Arold Oct 10 '13 at 11:54
having a separate library just to join the lines together seems like an overkill. Also, if we're going to use libraries, is there some reason to use Guava instead of [commons-lang](http://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/StringUtils.html#join%28java.lang.Iterable,%20java.lang.String%29)? `StringUtils.join(list, ", ");` seems simpler than this example. – eis Oct 22 '13 at 13:30
I haven't said Guava is the best. It's just an option. Also, I would say using Guava is an overkill - it's just an utility library. :) – Konstantin Yovkov Oct 22 '13 at 13:31

score 3 · Answer 3 · answered Oct 10 '13 at 11:52

3

Initialize your string to "":

 String strTest = "";

Alternatively, you should use a StringBuilder:

 StringBuilder builder = new StringBuilder();

 for (AlternativeEntity alternativeEntity : msg.Guidance()
  .getAlternatives()) {

     builder.append(alternativeEntity.getArrivalStation().getName()).append(", ");

 }

This will produce better performance.

answered Oct 10 '13 at 11:52

Evan Knowles

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Why the boilerplate? Why don't you use Guava for example. – Adam Arold Oct 10 '13 at 11:54
Also remove the last `,` after the loop. Your answer is the best, but nobody paid attention to that detail. – dic19 Oct 10 '13 at 11:56
Maybe also include about removing the trailing `", "`. – christopher Oct 10 '13 at 11:56

Amith · Answer 4 · 2013-10-22T13:18:37.483

1

Java provides StringBuilder class just for this purpose,its simple and easy to use..

    StringBuilder str = new StringBuilder("India ");

     //to append "Hi"
    str.append("Hi");

    // print the whole string
    System.out.println("The string is "+str)

the output will be : The string is India Hi

click here to know more about StringBuilder class

edited Oct 22 '13 at 13:18

answered Oct 10 '13 at 11:56

Amith

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score 0 · Answer 5 · answered Oct 10 '13 at 11:51

0

Replace String strTest = null; by String strTest = "";

answered Oct 10 '13 at 11:51

Julien

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score 0 · Answer 6 · answered Oct 10 '13 at 11:51

0

Change

 String strTest = null;

to

String strTest = "";

answered Oct 10 '13 at 11:51

Juned Ahsan

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score 0 · Answer 7 · answered Oct 10 '13 at 11:52

0

why don't you use:

String strTest = "";

and at the end:

if(strTest.endsWith(", "))
   strTest = strTest.substring(0, strTest.length()-2);

answered Oct 10 '13 at 11:52

vishal_aim

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score 0 · Answer 8 · answered Oct 10 '13 at 11:54

0

Initialize String strTest="";

For skipping the last comma',' Use outside For loop:

strTest = strTest.substring(0,strTest.trim().length()-1);

answered Oct 10 '13 at 11:54

Pranav Kale

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score 0 · Answer 9 · answered Oct 10 '13 at 12:00

String strTest = null;

for (AlternativeEntity alternativeEntity : msg.Guidance().getAlternatives()) {
  String name = alternativeEntity.getArrivalStation().getName();
  strTest = (strTest == null) ? name : strTest +  ", " + name;
}

If the list is long, you should use a StringBuilder rather than the String for strTest because the code above builds a fresh string on each iteration: far too much copying.

How to concatenate a String in Java without using a complex code structure?

9 Answers9