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:
- filter(predicate) Method
- sorted() Method
- distinct() Method
- map() Method
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 Program to illustrate Intermediate Methods of Streams
// Case 1: filter(predicate) Method
// Importing input output classes
import java.io.*;
// Importing List Class from java.util package
import java.util.List;
// Main Class
public class JavaHubPoint{
// 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+ " ")
);
}
}
Output
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 Program to illustrate Intermediate Method of Stream
// Case 2: sorted() Method
// Importing input output class
import java.io.*;
// Importing List class from java.util package
import java.util.List;
// Main class
class JavaHubPoint{
// 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);
}
}
Output
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 Program to illustrate Intermediate Method of Stream
// Case 3: distinct() Method
// Importing input output classes
import java.io.*;
// Importing List class from java.util package
import java.util.List;
// Main Class
class JavaHubPoint{
// 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);
}
}
Output
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 Program to illustrate Intermediate Stream Methods
// Case 4: map() Method
// Importing input output class
import java.io.*;
// Importing List class from the java.util package
import java.util.List;
// Main Class
class JavaHubPoint{
// 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);
}
}
Output
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