In this article, we will learn the use of joining() method in Java 8 Collectors API with the help of examples.
Table of contents
Definition
The joining() method of the Collectors class is used to join a series of Characters or Strings into a single String object. The Characters or Strings will be concatenated in the same order as it is provided.
Overloaded methods
The joining() method is overloaded in 3 ways:
- static Collector joining()
- static Collector joining(CharSequence delimiter)
- static Collector joining(CharSequence delimiter, CharSequence prefix, CharSequence suffix)
static Collector joining()
This method returns a Collector that concatenates or joins the input elements into a String. The joining() method will maintain the order of the input elements. This is the simplest form of joining.
Example 1: We will join the names from a list of Persons
Person.java
package com.getinputs;
public class Person {
String name;
int age;
Person(String name, int age)
{
this.name=name;
this.age=age;
}
public String getName() {
return name;
}
public int getAge() {
return age;
}
@Override
public String toString() {
return "Person{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}
}
Joining.java
package com.getinputs;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
public class Joining {
static List<Person> createPeople()
{
List<Person> list = new ArrayList<>();
list.add(new Person("Suraj ", 32));
list.add(new Person("Iqbal ", 34));
list.add(new Person("Suchit ", 25));
list.add(new Person("Amar ", 30));
list.add(new Person("Kartik ", 32));
return list;
}
public static void main(String[] args) {
List<Person> list = createPeople();
String str = list.stream().map(person -> person.getName()).collect(Collectors.joining());
System.out.println(str);
}
}
Output : Suraj Iqbal Suchit Amar Kartik
Example 2: We will join the array of Characters to create a String
JoiningChars .java
package com.getinputs;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class JoiningChars {
public static void main(String[] args) {
char[] chars = {'g','e','t','i','n','p','u','t','s','.','c','o','m'};
String str = Stream.of(chars)
.map(String::valueOf)
.collect(Collectors.joining());
System.out.println(str);
}
}
Output : getinputs.com
static Collector joining(CharSequence delimiter)
This method returns a Collector that concatenates or joins the input elements into a String using a delimiter. The joining() method will maintain the order of the input elements.
Note* delimiter is a symbol or char sequence to join the elements.
Example 1: We will join the names from a list of Persons using a comma delimiter.
Joining.java
package com.getinputs;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
public class Joining {
static List<Person> createPeople()
{
List<Person> list = new ArrayList<>();
list.add(new Person("Suraj", 32));
list.add(new Person("Iqbal", 34));
list.add(new Person("Suchit", 25));
list.add(new Person("Amar", 30));
list.add(new Person("Kartik", 32));
return list;
}
public static void main(String[] args) {
List<Person> list = createPeople();
String str = list.stream().map(person -> person.getName()).collect(Collectors.joining(","));
System.out.println(str);
}
}
Output: Suraj,Iqbal,Suchit,Amar,Kartik
Example 2: We will join the list of String with a comma delimiter
JoiningStrings .java
package com.getinputs;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
public class JoiningStrings {
public static void main(String[] args) {
List<String> list = Arrays.asList("hello", "getinputs", "com");
String str = list.stream().collect(Collectors.joining(","));
System.out.println(str);
}
}
Output: hello,getinputs,com
static Collector joining(CharSequence delimiter, CharSequence prefix, CharSequence suffix)
This method returns a Collector that concatenates or joins the input elements into a String using a delimiter along with a prefix and a suffix.
- The delimiter is a symbol to join the elements
- A prefix is a symbol that we will append at the start of the first element
- A suffix is a symbol that we will append after the last element of the string
Example 1: We will join the names from a list of Persons using a comma delimiter and add square brackets at the start and end of the String.
Joining .java
package com.getinputs;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
public class Joining {
static List<Person> createPeople()
{
List<Person> list = new ArrayList<>();
list.add(new Person("Suraj", 32));
list.add(new Person("Iqbal", 34));
list.add(new Person("Suchit", 25));
list.add(new Person("Amar", 30));
list.add(new Person("Kartik", 32));
return list;
}
public static void main(String[] args) {
List<Person> list = createPeople();
String str = list.stream().map(person -> person.getName()).collect(Collectors.joining(",", "[", "]"));
System.out.println(str);
}
}
Output : [Suraj,Iqbal,Suchit,Amar,Kartik]
Example 2: We will join the list of String using a comma delimiter and add braces at the start and end of the String
JoiningStrings .java
package com.getinputs;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
public class JoiningStrings {
public static void main(String[] args) {
List<String> list = Arrays.asList("hello", "getinputs", "com");
String str = list.stream().collect(Collectors.joining(",", "{", "}"));
System.out.println(str);
}
}
Output : {hello,getinputs,com}
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