Java String Join() method Signature Returns a new String composed of copies of the CharSequence elements joined together with a copy of the specified delimiter. The first argument of this method specifies the delimiter that is used to join multiple strings. Note that if an element is null, then “null” is added.
Using + Operator The + operator is one of the easiest ways to concatenate two strings in Java that is used by the vast majority of Java developers. We can also use it to concatenate the string with other data types such as an integer, long, etc.
Apache's commons lang is your friend here - it provides a join method very similar to the one you refer to in Ruby:
StringUtils.join(java.lang.Iterable,char)
Java 8 provides joining out of the box via StringJoiner
and String.join()
. The snippets below show how you can use them:
StringJoiner
StringJoiner joiner = new StringJoiner(",");
joiner.add("01").add("02").add("03");
String joinedString = joiner.toString(); // "01,02,03"
String.join(CharSequence delimiter, CharSequence... elements))
String joinedString = String.join(" - ", "04", "05", "06"); // "04 - 05 - 06"
String.join(CharSequence delimiter, Iterable<? extends CharSequence> elements)
List<String> strings = new LinkedList<>();
strings.add("Java");strings.add("is");
strings.add("cool");
String message = String.join(" ", strings);
//message returned is: "Java is cool"
You could write a little join-style utility method that works on java.util.Lists
public static String join(List<String> list, String delim) {
StringBuilder sb = new StringBuilder();
String loopDelim = "";
for(String s : list) {
sb.append(loopDelim);
sb.append(s);
loopDelim = delim;
}
return sb.toString();
}
Then use it like so:
List<String> list = new ArrayList<String>();
if( condition ) list.add("elementName");
if( anotherCondition ) list.add("anotherElementName");
join(list, ",");
In the case of Android, the StringUtils class from commons isn't available, so for this I used
android.text.TextUtils.join(CharSequence delimiter, Iterable tokens)
http://developer.android.com/reference/android/text/TextUtils.html
The Google's Guava library has com.google.common.base.Joiner class which helps to solve such tasks.
Samples:
"My pets are: " + Joiner.on(", ").join(Arrays.asList("rabbit", "parrot", "dog"));
// returns "My pets are: rabbit, parrot, dog"
Joiner.on(" AND ").join(Arrays.asList("field1=1" , "field2=2", "field3=3"));
// returns "field1=1 AND field2=2 AND field3=3"
Joiner.on(",").skipNulls().join(Arrays.asList("London", "Moscow", null, "New York", null, "Paris"));
// returns "London,Moscow,New York,Paris"
Joiner.on(", ").useForNull("Team held a draw").join(Arrays.asList("FC Barcelona", "FC Bayern", null, null, "Chelsea FC", "AC Milan"));
// returns "FC Barcelona, FC Bayern, Team held a draw, Team held a draw, Chelsea FC, AC Milan"
Here is an article about Guava's string utilities.
In Java 8 you can use String.join()
:
List<String> list = Arrays.asList("foo", "bar", "baz");
String joined = String.join(" and ", list); // "foo and bar and baz"
Also have a look at this answer for a Stream API example.
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