The Stream API is used to process collections of objects. A stream is a sequence of objects that supports various methods which can be pipelined to produce the desired result. The method provided by the stream are broadly categorized as
- Intermediate Methods
- Terminal Methods
Here, we will be discussing the Intermediate methods of the Stream API. All these methods are in java.util.stream.Stream. Intermediate operators do not execute until a terminal operation is invoked, i.e. they are not executed until a result of processing is actually needed. We will be discussing a few of the important and most frequently used:
Method 1: filter(predicate)
It returns a new stream consisting of the elements of the stream from which it is called which are according to the predicate (condition).
Note:
- Intermediate functions return a stream back.
- On any stream you can execute any number of intermediate operations, but the terminal operation should be single and written at last. So following are the intermediate methods provided by the Stream
- Predicate is a non-interfering, stateless predicate to apply to each element to determine if it should be included or not.
Example
Java
// Java Program to illustrate Intermediate Methods of Streams// Case 1: filter(predicate) Method // Importing input output classesimport java.io.*;// Importing List Class from java.util package import java.util.List;// Main Classpublic class GFG { // Main driver method public static void main (String[] args) { // Creating an object of List Class by // declaring a list of Integers // Custom entries in the list elements List<Integer> intList = List.of(15,20,48,63,49,27,56,32,9); // Calling the function to // print the list of Even numbers printEvenNumber(intList); } // Method 2 // Helper method // To print the even numbers using filter method. private static void printEvenNumber(List<Integer> intList){ // Display message System.out.print("\nEven numbers are : "); // Illustrating filter method usage intList.stream().filter( element -> (element%2==0) ) .forEach( element -> System.out.print(element+ " ") ); }} |
Even numbers are : 20 48 56 32
Method 2: sorted()
Returns a stream consisting of the elements of the stream passed, sorted according to the natural order. If the elements of this stream are not comparable, a java.lang.ClassCastException may be thrown when the terminal operation is executed.
Example
Java
// Java Program to illustrate Intermediate Method of Stream// Case 2: sorted() Method// Importing input output classimport java.io.*;// Importing List class from java.util packageimport java.util.List;// Main classclass GFG { // Method 1 // To print the elements of the Sorted List public static void printSortedList(List<Integer> intList) { // Sorts and returns the stream to the forEach // illustrating stream method intList.stream().sorted().forEach( element -> System.out.println(element)); } // Method 2 // Main driver method public static void main(String[] args) { // Creating an object of List class // Declaring object of Integer type // Custom entries List<Integer> intList = List.of(68, 45, 99, 21, 8, 76, 34, 19); // Display message only System.out.println( "Elements of Sorted List are as follows : "); // Calling the method to print the Sorted List printSortedList(intList); }} |
8 19 21 34 45 68 76 99
Method 3: distinct()
It returns a stream consisting of the distinct(different) elements of the passed stream. For ordered stream, the selection of the distinct elements is stable (For duplicated elements, the element appearing first in the encounter order is preserved). While for non-ordered streams it does not make any guarantee for stability.
Example
Java
// Java Program to illustrate Intermediate Method of Stream// Case 3: distinct() Method// Importing input output classesimport java.io.*;// Importing List class from java.util packageimport java.util.List;// Main Classclass GFG { // Method 1 // To find distinct elements from the List public static void findDistinctElements(List<Integer> intList) { intList.stream().distinct().forEach( element -> System.out.print(element + " ")); // Display message only System.out.println("\n\nSorted List is "); // Also we are sorting elements at the same time intList.stream().distinct().sorted().forEach( element -> System.out.print(element + " ")); } // Method 2 // Main driver method public static void main(String[] args) { // Creating an object of List class // Declaring object of Integer type // Custom integer inputs List<Integer> intList = List.of(12, 54, 63, 12, 7, 98, 63, 54, 72); // Calling the Method 1 as above created to // find the distinct elements from the list findDistinctElements(intList); }} |
12 54 63 7 98 72 Sorted List is 7 12 54 63 72 98
Method 4: map()
Mapper is a non-interfering, stateless function to apply to each element of the stream. It returns a stream consisting of the results of applying the given function to the element of the passed stream.
Syntax:
stream().map(mapper)
Implementation:
Example
Java
// Java Program to illustrate Intermediate Stream Methods// Case 4: map() Method// Importing input output classimport java.io.*;// Importing List class from the java.util packageimport java.util.List;// Main Classclass GFG { // Method 1 // To find the cube of elements in the List public static void findTheCube(List<Integer> intList) { intList.stream() .map(element -> element * element * element) .forEach( element -> System.out.print(element + " ")); // Display message only System.out.println( "\n\nOutput after distinct() implementation : "); // Applying distinct() on this intList.stream() .distinct() .map(element -> element * element * element) .forEach( element -> System.out.print(element + " ")); // Display message only System.out.println( "\n\nOutput after sorted() implementation : "); // Now applying sorted() on this intList.stream() .distinct() .sorted() .map(element -> element * element * element) .forEach( element -> System.out.print(element + " ")); // Display message only System.out.println( "\n\nOutput after filter() implementation : "); // Applying Filter() that values // only below 10000 will be printed intList.stream() .distinct() .sorted() .map(element -> element * element * element) .filter(element -> element < 10000) .forEach( element -> System.out.print(element + " ")); } // Method 2 // Main driver method public static void main(String[] args) { // Creating an object of List class and // declaring object of Integer type // Custom entries List<Integer> intList = List.of(5, 19, 8, 23, 6, 54, 32, 5, 23); // Calling the Method1 in the main() body // to get the cube of the elements in the List findTheCube(intList); }} |
125 6859 512 12167 216 157464 32768 125 12167 Output after distinct() implementation : 125 6859 512 12167 216 157464 32768 Output after sorted() implementation : 125 216 512 6859 12167 32768 157464 Output after filter() implementation : 125 216 512 6859
