Join Strings with Collectors
Description
The joining() method from Collectors class returns a collector that concatenates the stream of CharSequence and returns the result as a String.
The joining() method is overloaded and it has three versions:
- joining()
concatenates all elements - joining(CharSequence delimiter)
uses a delimiter to be used between two elements. - joining(CharSequence delimiter, CharSequence prefix, CharSequence suffix)
uses a delimiter, a prefix and a suffix. The prefix is added to the beginning and the suffix is added to the end.
Example
The following code shows how to use the joining() method.
import java.time.LocalDate;
import java.time.Month;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
//w w w . j a v a2 s. c o m
public class Main {
public static void main(String[] args) {
List<Employee> persons = Employee.persons();
String names = persons.stream()
.map(Employee::getName)
.collect(Collectors.joining());
String delimitedNames = persons.stream()
.map(Employee::getName)
.collect(Collectors.joining(", "));
String prefixedNames = persons.stream()
.map(Employee::getName)
.collect(Collectors.joining(", ", "Hello ", ". Goodbye."));
System.out.println("Joined names: " + names);
System.out.println("Joined, delimited names: " + delimitedNames);
System.out.println(prefixedNames);
}
}
class Employee {
public static enum Gender {
MALE, FEMALE
}
private long id;
private String name;
private Gender gender;
private LocalDate dob;
private double income;
public Employee(long id, String name, Gender gender, LocalDate dob,
double income) {
this.id = id;
this.name = name;
this.gender = gender;
this.dob = dob;
this.income = income;
}
public String getName() {
return name;
}
public static List<Employee> persons() {
Employee p1 = new Employee(1, "Jake", Gender.MALE, LocalDate.of(1971,
Month.JANUARY, 1), 2343.0);
Employee p2 = new Employee(2, "Jack", Gender.MALE, LocalDate.of(1972,
Month.JULY, 21), 7100.0);
Employee p3 = new Employee(3, "Jane", Gender.FEMALE, LocalDate.of(1973,
Month.MAY, 29), 5455.0);
Employee p4 = new Employee(4, "Jode", Gender.MALE, LocalDate.of(1974,
Month.OCTOBER, 16), 1800.0);
Employee p5 = new Employee(5, "Jeny", Gender.FEMALE, LocalDate.of(1975,
Month.DECEMBER, 13), 1234.0);
Employee p6 = new Employee(6, "Jason", Gender.MALE, LocalDate.of(1976,
Month.JUNE, 9), 3211.0);
List<Employee> persons = Arrays.asList(p1, p2, p3, p4, p5, p6);
return persons;
}
}
The code above generates the following result.
