StringJoiner in Java 8

22 / Jun / 2016 by Nishant Lakra 1 comments

Being a programmer, at some point of time we encountered a situation in which you wanted to join (not concat) multiple strings of delimited items in Java. Worst can be if you are provided multiple string literals. Just think for a second and how will you build a string of delimited items using these literals. Eg.

[java]
String str1 = "java";
String str2 = "scala";
String str3 = "groovy";

StringBuilder sb = new StringBuilder();
sb.append(str1).append(",").append(str2).append(",").append(str3);
sb.toString();

[/java]

Or, many times we find ourselves in a situation where you want to pass a collection to IN clause of HQL or SQL. In this era of programming this is how we do this so obvious work

[java]
// List<String> listOfNames = ….
StringBuilder sbObj = new StringBuilder();
for (String str : listOfNames) {
if (sbObj.length() > 0) {
sbObj.append(‘,’);
}
sbObj.append(str);
}
sbObj.toString();

[/java]

Code reviewer will acquit you due to lack of good solutions evidence. But not anymore, In Java 8 we finally can join Strings with ease.

StringJoiner is a class added in Java 8. As the name suggests, we can use this class to join strings. There are two constructors, one taking the separator (delimiter) and one allowing a prefix and suffix.

1. StringJoiner(CharSequence delimiter)

[java]
StringJoiner joiner = new StringJoiner(",");
joiner.add("java");
joiner.add("scala");
joiner.add("groovy");
String desiredStr = joiner.toString(); // "java,scala,groovy"

// add() calls can be chained
joined = new StringJoiner("-")
.add("java")
.add("scala")
.add("groovy")
.toString(); // "java-scala-groovy"
[/java]

2. StringJoiner(CharSequence delimiter, CharSequence prefix, CharSequence suffix)

The String like “[Richard:Gilfoyle:Erlich]” may be constructed as follows:

[java]
StringJoiner sj = new StringJoiner(":", "[", "]");
sj.add("Richard").add("Gilfoyle").add("Erlich");
String desiredString = sj.toString();
[/java]

Moreover, StringJoiner is used as a behind scene tool by the two new static join() methods of String class:

//  join(CharSequence delimiter, CharSequence… elements)

[java]
String joined = String.join("/", "2016", "06", "15" ); // "2016/06/15"
[/java]

// join(CharSequence delimiter, Iterable<? extends CharSequence> elements)

[java]
List<String> list = Arrays.asList("java", "scala", "groovy");
joined = String.join(";", list); // "java;scala;groovy"
[/java]

A new joining Collector is also available for the new Stream API:

[java]
List<Employee> list = Arrays.asList(
new Employee("Richard", "Hendriks"),
new Employee("Erlich", "Bachmann"),
new Employee("Jared", "Dunn ")
);

String joinedFirstNames = list.stream()
.map(Employee::getFirstName)
.collect(Collectors.joining(","));

// "Richard, Erlich, Jared"

[/java]

Now,  join string smartly 😉

Tag -

Java java8 String
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