Updated April 15, 2023
Introduction to Java 8 Collections
Basically, Java 8 provides the different kinds of interfaces of the framework to the user in which that collection is one of the interfaces that are provided by java. Normally a collection is a root interface of a framework as well as it provides the different types of classes, by using this collection we can represent the group of objects as a single unit. Basically, java 8 releases several different kinds of features to the user. It is used for functional programming, JavaScript, and API manipulation as per user requirements. The collection is one type of framework used to programming easily compared to the other framework.
What is Java 8 collections?
The Collections in Java 8 gives a design to store and control the gathering of items, interfaces, and classes. This java assortment is a structure. This structure has a few helpful capacities that have huge loads of valuable capacities, making a software engineer task very simple.
This system gives numerous interfaces (Queue, Set, List, Deque) and classes ( PriorityQueue, HashSet, ArrayList, Vector, LinkedList, LinkedHashSet).
- The Collection structure is a brought-together design for putting away and controlling a gathering of items.
- The assortment structure was intended to meet a few objectives, for example, −
- The structure must be elite and adjust an assortment of simple strategies.
- The executions for the key assortments were to be profoundly effective.
- The structure needed to permit various sorts of assortments to work likewise.
- The structure needed to expand as well as adjust an assortment without any problem.
What is the Use of Java 8 collection framework?
Now let’s see why we need to use the Java 8 collection framework as follows.
Assume, A variable is made to store information, and a 15 worth is relegated (Example, int X =15). Presently the developer needs to store one more piece of information of the equivalent data type. Thus, the developer needs to make another variable and allot another worth (Example, int Y= 25).
Assuming the developer needs to store 150 qualities then the drawback of this is the software engineer needs to make various factors with a special name and it is extremely tedious too.
For this situation, an exhibit idea is presented. The developer pronounces a cluster with explicit size and store components.
All predefined executions can be found in the Collectors class. It’s generally expected practice to utilize the accompanying static import with them to use expanded coherence:
import static java.util.stream.Collectors.*;As per our requirement, we can import the single collectors as follows.
import static java.util.stream.Collectors.toList;
import static java.util.stream.Collectors.toMap;
import static java.util.stream.Collectors.toSet;
Now let’s see the different methods of collections as follows.
Collectors.toList()
The toList authority can be utilized for gathering all Stream components into a List occurrence. The significant thing to recollect is that we can’t accept a specific List execution with this strategy. Assuming we need to have more power over this, we can utilize toCollection all things considered.
How about we make a Stream occurrence addressing a grouping of components, and afterwards gather them into a List of occasions:
List<String> specified name = provided_list_name.stream() .collect(toList());Collectors.toSet()
Collectors toSet() returns a Collector that aggregates the information components into another Set. There are no certifications on the kind, alterability, serializability, or string security of the Set returned. This is an unordered Collector i.e, the assortment activity doesn’t focus on saving the experience request of information components.
Example
import java.util.Set;
import java.util.stream.Collectors;
import java.util.stream.Stream;
class sample {
public static void main(String[] args)
{
Stream<String> s_obj = Stream.of("Welcome",
"In",
"Java 8",
"Collection");
Set<String> Set_obj = s_obj.collect(Collectors.toSet());
System.out.println(Set_obj);
}
}Explanation
In the above example, we try to implement Collectors.toSet(). The end output of the above code we illustrated by using the following screenshot as follows.
Collectors.toCollection()
Collectors toCollection(Supplier<C> collectionFactory) technique in Java is utilized to make a Collection utilizing Collector. It returns a Collector that aggregates the info components into another Collection, in the request where they are passed.
Example
Now let’s see the example of the Collectors.toCollection() method for better understanding as follows.
import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.Stream;
class Main{
public static void main(String[] args)
{
Stream<String> s_obj = Stream.of("Welcome", "In", "Java 8", "Collection");
Collection<String> c_obj= s_obj.collect(Collectors.toCollection(TreeSet::new));
System.out.println(c_obj);
}
}Explanation
In the above code we try to implement Collectors.toCollection(). The end output of the above code we illustrated by using the following screenshot as follows.
Collectors.toMap()
The toMap collector can be utilized to gather Stream components into a Map occurrence. To do this, we need to give two capacities:
keyMapper
valueMapper
We’ll utilize keyMapper to remove a Map key from a Stream component, and valueMapper to extricate a value related to a given key.
We should gather those components into a Map that stores strings as keys and their lengths as qualities. The toMap() technique is a static strategy for Collectors class which returns a Collector that aggregates components into a Map whose keys and values are the consequence of applying the gave planning capacities to the info components. Note that keys are remarkable and assuming regardless the keys are copied, an IllegalStateException is tossed when the assortment activity is performed.
import java.util.stream.Collectors;
import java.util.stream.Stream;
import java.util.*;
public class Main {
public static void main(String[] args)
{
Stream<String[]>
S_obj = Stream.of(new String[][] { { "Hi", "Welcome" },
{"C", "collection" },
{ "J", "Java" } });
Map<String, String>
map_obj = S_obj.collect(
Collectors.toMap(a -> a[0], a -> a[1]));
System.out.println("Map:" + map_obj);
}
}Explanation
In the above code, we try to implement Collectors.toMap(). The end output of the above code we illustrated by using the following screenshot as follows.
Collectors.collectingAndThen()
The collectingAndThen(Collector downstream, Function finisher) technique for class authorities in Java, which embraces Collector so we can play out an extra completing change.
import java.util.Collections;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class sample {
public static void main(String[] args)
{
List<String> l_obj
= Stream
.of("Hi", "Welcome", "Collection")
.collect(Collectors
.collectingAndThen(
Collectors.toList(),
Collections::<String> unmodifiableList));
System.out.println(l_obj);
}
}Explanation
In the above code we try to implement Collectors.collectingAndThen(). The end output of the above code we illustrated by using the following screenshot as follows.
Conclusion
We hope from this article you learn more about the java 8 collections. From the above article, we have taken in the essential idea of the java 8 collections and we also see the representation and example of java 8 collections. From this article, we learned how and when we use the java 8 collections.
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