In this article, we will discuss how to convert List into Stream in Java 1.8 version using stream() method

1. Using stream() method

List to Stream is a straight-forward conversion using stream() method
After converting to Stream, further processing is also possible through series of intermediate operations but final result won’t be yielded until terminal operation is executed
Read Intermedicate operation v/s terminal operation

ListToStreamConversion.java

package net.bench.resources.stream.to.list;

import java.util.Arrays;
import java.util.List;
import java.util.stream.Stream;

public class ListToStreamConversion {

	public static void main(String[] args) {

		// 1. define list
		List<String> names = Arrays.asList(
				"Rajiv",
				"Anbu",
				"Santosh",
				"Abdul",
				"Lingaraj"
				);


		// 2. convert List to Stream
		Stream<String> nameStream = names.stream();


		// 3. print to Stream elements using forEach looping
		System.out.println("Stream elements : \n");
		nameStream.forEach(name -> System.out.println(name));
	}
}

Output:

Stream elements : 

Rajiv
Anbu
Santosh
Abdul
Lingaraj

2. List to Stream :

Using stream() method
1. Convert to Stream and then filter using filter() method of Stream API
2. Convert to Stream and then tranform to another form using map() method of Stream API

2.1 Filter a Stream using Predicate

We can apply Predicate to Stream elements using filter() method of Stream API after converting List to Stream to remove unwanted items/elements from Stream (or in other words to get desired result)
Predicate can be defined separately and its instance can be passed to filter() method or pass lambda-expression as mentioned below
Lambda-expression :- filter(name -> name.startsWith(“A”))

ConvertToStreamAndFilter.java

package net.bench.resources.stream.to.list;

import java.util.Arrays;
import java.util.List;
import java.util.stream.Stream;

public class ConvertToStreamAndFilter {

	public static void main(String[] args) {

		// 1. define list
		List<String> names = Arrays.asList(
				"Rajiv",
				"Anbu",
				"Santosh",
				"Abdul",
				"Lingaraj"
				);


		// 2. convert List to Stream
		Stream<String> nameStream = names.stream();


		// 3. print to console
		System.out.println("Stream filtering : \n");


		// 4. filter and print
		nameStream
		.filter(name -> name.startsWith("A"))
		.forEach(System.out::println);
	}
}

Output:

Stream filtering : 

Anbu
Abdul

2.2 Map a Stream using Function

Function can be applied to Stream elements using map() method of Stream API after converting List to Stream
map() method transform Stream elements from one form to another form for example, converting all cases of Stream elements into upper case
Function can be defined separately and its instance can be passed to map() method or pass lambda-expression as mentioned below
Lambda-expression :- map(name -> name.toUpperCase())

ConvertToStreamAndMapToUpperCase.java

package net.bench.resources.stream.to.list;

import java.util.Arrays;
import java.util.List;
import java.util.stream.Stream;

public class ConvertToStreamAndMapToUpperCase {

	public static void main(String[] args) {

		// 1. define list
		List<String> names = Arrays.asList(
				"Rajiv",
				"Anbu",
				"Santosh",
				"Abdul",
				"Lingaraj"
				);


		// 2. convert List to Stream
		Stream<String> nameStream = names.stream();


		// 3. print to console
		System.out.println("Stream elements in Upper case : \n");


		// 4. filter and print
		nameStream
		.map(name -> name.toUpperCase())
		.forEach(System.out::println);
	}
}

Output:

Stream elements in Upper case : 

RAJIV
ANBU
SANTOSH
ABDUL
LINGARAJ

References:

Happy Coding !!
Happy Learning !!

BenchResources.Net

Java tutorial for beginners

1. Using stream() method

ListToStreamConversion.java

2. List to Stream :

2.1 Filter a Stream using Predicate

ConvertToStreamAndFilter.java

2.2 Map a Stream using Function

ConvertToStreamAndMapToUpperCase.java

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