StreamJava8Part2

//Stream Operations Part 2

import java.util.stream.*;
import java.util.*;
import java.util.Comparator;
public class MyClass {
    public static void main(String args[]) {
      createStreamAndGetFirstElement();
      createStreamAndGetLastElement();
      duplicateInStream();
      countOccurenceOfChar('?');
      getArrayListFromStream();
    }
    //Create a stream of string and find the first element in the stream
    public static void createStreamAndGetFirstElement(){
        //-----------------------------using reduce----------------------------------------------
        //if we do not use orElse, it returns an Optional object not string
        Stream<String> s=Stream.of("Hey","Hello","Hi","Hola");
        System.out.println(s.reduce((first,second)->first).orElse(null));
        /*Output:
            Hey
        */
        //----------------------------------------------------------------------------------------
        
        //----------------------------using findFirst---------------------------------------------
        s=Stream.of("Hey","Hello","Hi","Hola");
        System.out.println(s.findFirst().orElse(null));
        /*Output:
            Hey
        */
        //----------------------------------------------------------------------------------------
        
        //---------------checking same operation on null/empty stream-----------------------------
        //checking same operation on null/empty stream
        s=Stream.empty();
        System.out.println(s.findFirst().orElse(null));
        /*Output:
            null
        */
        //----------------------------------------------------------------------------------------
    }
    //Create a stream of string and find the last element in the stream
    public static void createStreamAndGetLastElement(){
        //--------------------------------using reduce--------------------------------------------
        Stream<String> s=Stream.of("Hey","Hello","Hi","Hola");
        System.out.println(s.reduce((first,second)->second).orElse(null));
        /*Output:
            Hola
        */
        //----------------------------------------------------------------------------------------
        
        //--------------------------------using skip----------------------------------------------
        s=Stream.of("Hey","Hello","Hi","Hola");
        int N=4;
        System.out.println(s.skip(N-1).findFirst().orElse(null));
        /*Output:
            Hola
        */
        //----------------------------------------------------------------------------------------
        
        //---------------------using sorted reverse order------------------------------------------
        s=Stream.of("Hey","Hello","Hi","Hola");
        System.out.println(s.sorted(Comparator.reverseOrder()).findFirst().orElse(null));
        /*Output:
            Hola
        */
        //----------------------------------------------------------------------------------------
    }
    //find duplicate elements in a stream
    public static void duplicateInStream(){
        
        //---------------------using Set.add()---------------------------------------------------
        //add returns false if element already present
        Stream<Integer> s=Stream.of(1,2,3,4,2,5,6,1,3,3);
        Set<Integer> set=new HashSet<>();
        s.filter(i->!set.add(i)).collect(Collectors.toSet()).forEach(System.out::println);
        /*Output:
            1
            2
            3
        */
        //----------------------------------------------------------------------------------------
        
        //---------------------using Collections.frequency()--------------------------------------
        //works with collection only
        //To understand how frequency() works, visit https://www.geeksforgeeks.org/java-util-collections-frequency-java/
        List<Integer> list = Arrays.asList(1,2,3,4,2,5,6,1,3,3);
        list.stream().filter(i->Collections.frequency(list,i)>1).collect(Collectors.toSet()).forEach(System.out::println);
        /*Output:
            1
            2
            3
        */
        //----------------------------------------------------------------------------------------
    }
    //Count occurence of a given character in a given string
    public static void countOccurenceOfChar(char toFind){
        
        //-----------------------------using chars()----------------------------------------------
        String s="Hey Siri, how you doing?";
        System.out.println("Occurences of Character "+toFind+" -> "+s.chars().filter(i -> i==toFind).count());
        /*Output:
        Occurences of Character ? -> 1
        */
        //----------------------------------------------------------------------------------------
    }
    //Get arrayList from Stream
    public static void getArrayListFromStream(){
        //----------------------Collectors.toList()-----------------------------------------------
        Stream<Integer> s=Stream.of(1,2,3,4,2,5,6,1,3,3);
        s.collect(Collectors.toList()).forEach(System.out::print);
        //----------------------------------------------------------------------------------------
        /*Output:
        1234256133
        */
        //----------------------------------------------------------------------------------------
        
        //----------------------Collectors.toCollection()----------------------------------------
        //a more generic way for collections overall
        s=Stream.of(1,2,3,4,2,5,6,1,3,3);
        s.collect(Collectors.toCollection(ArrayList::new)).forEach(System.out::print);
        //----------------------------------------------------------------------------------------
        /*Output:
        1234256133
        */
        //----------------------------------------------------------------------------------------
        
        //----------------------Collectors.toCollection()-----------------------------------------
        //making set instead of list
        s=Stream.of(1,2,3,4,2,5,6,1,3,3);
        s.collect(Collectors.toCollection(HashSet::new)).forEach(System.out::print);
        //----------------------------------------------------------------------------------------
        /*Output:
        123456
        */
        //-----------------------------------------------------------------------------------------
    }
}