Stream Code Interview Questions

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  1. What is the Difference between Map and Filter?
    Both perform intermediate Operations and returns stream as output.By using map, you transform the object values.
    Map returns a stream consisting of the results of applying the given function to the elements of this stream. In a simple sentence, the map returns the transformed object value.
    Filter is used for filtering the data, it always returns the boolean value. If it returns true, the item is added to list else it is filtered out (ignored)
  2. Find the Sum of Nos in List? 
    public class ReduceEgs {
    public static void main(String[] args) {
        List<Integer> arrNumbers =  Arrays.asList(1,2,3,4,5,6,7,8,9);

        Integer sum = arrNumbers.stream().reduce(0, Integer::sum);
        Integer sum2 = arrNumbers.stream().reduce(0, (x,y)->x+y);
        Integer sum3 = arrNumbers.stream().reduce(0, ReduceEgs::sumNos);
    }

    public static Integer sumNos(int x, int y){
        System.out.println("a -"+ x + " b - "+  y);
        return x+y;
    }
}
  3. Find the Min and Max in Nos List? 
     public static void main(String[] args) {
        List<Integer> arrNumbers =  Arrays.asList(1,2,3,4,5,-6,7,-8,9);

        arrNumbers =  Arrays.asList(-5,-6,-8);
        Integer Max = arrNumbers.stream().reduce(0, (x,y)->x>y?x:y);
        System.out.println("Output 1 ="+ Max);

        //Its good to start with Identity as Negative Value in order to address negative Integer Comparison
        //If you start with 0 then 0 would be returned like above
        Integer Max2 = arrNumbers.stream().reduce(Integer.MIN_VALUE, (x,y)->x>y?x:y);
        System.out.println("Output 2 ="+ Max2);

        arrNumbers =  Arrays.asList(5,6,8);

        Integer Min = arrNumbers.stream().reduce(0, (x,y)->x<y?x:y);
        System.out.println("Output 3 ="+ Min);

        //Its good to start with Identity as Max Positive Value in order to address Integer Comparison
        Integer Min2 = arrNumbers.stream().reduce(Integer.MAX_VALUE, (x,y)->x<y?x:y);
        System.out.println("Output 4 ="+ Min2);
    }

    Output

    Output 1 =0
Output 2 =-5
Output 3 =0
Output 4 =5
  4. Find the Sum of Square of Nos in List? 
    public class ReduceEgs {
    public static void main(String[] args) {
        List<Integer> arrNumbers =  Arrays.asList(1,2,3);

        Integer squareSum = arrNumbers.stream().map(x->x*x).reduce(0, Integer::sum);
        System.out.println("Output 1 ="+ squareSum);
    }
}

    Output

    Output 1 =14
  5. Find the Sum of Odd Nos in List? 
    public class ReduceEgs {
    public static void main(String[] args) {
        List<Integer> arrNumbers =  Arrays.asList(1,2,3);

        Integer squareSum = arrNumbers.stream().filter(x-> x%2==1).reduce(0, Integer::sum);
        System.out.println("Output 1 ="+ squareSum);
    }
}

    Output

    Output 1 =4
  6. Distinct elements from List? 
    public class ReduceEgs {
    public static void main(String[] args) {
        List<Integer> arrNumbers =  Arrays.asList(1,2,3,1,4,2);

        System.out.println("Output 1");
        arrNumbers.stream().distinct().forEach(System.out::println);
    }
}

    Output

    Output 1
1
2
3
4
  7. Sort Elements in List? 
     public static void main(String[] args) {
   List<Integer> arrNumbers =  Arrays.asList(1,2,3,1,4,2);

   System.out.println("Output 2");
   arrNumbers.stream().sorted().forEach(System.out::println);
}

    Output

    Output 2
1
1
2
2
3
4
  8. Sorting based on Natural Order, Reverse Order and Length of String? 
    public static void main(String[] args) {
        List<String> arrSkills = Arrays.asList("Java", "Python",  "Ant");

        System.out.println("Sorting in Natural Order");
        arrSkills.stream().sorted(Comparator.naturalOrder()).forEach(System.out::println);

        System.out.println("Sorting in Reverse Order");
        arrSkills.stream().sorted(Comparator.reverseOrder()).forEach(System.out::println);

        System.out.println("Sorting based on Length");
        arrSkills.stream().sorted(Comparator.comparing(str -> str.length())).forEach(System.out::println);

    }

    Output

    Sorting in Natural Order
Ant
Java
Python
Sorting in Reverse Order
Python
Java
Ant
Sorting based on Length
Ant
Java
Python
  9. Collect the Elements in the List – Collect Even Nos and Length of String ? 
        public static void main(String[] args) {
        List<Integer> arrNumbers = Arrays.asList(1,2,4,5,7,6);
        List<String> arrNames = Arrays.asList("Java", "Oracle", "Maven", "Ant");

        System.out.println("Collect Even Nos in list");
        List<Integer> arrEvenNumbers = arrNumbers.stream().filter(x->x%2==0).collect(Collectors.toList());
        arrEvenNumbers.stream().forEach(System.out::println);

        System.out.println("Length of Elements");
        List<Integer> arrEvenNumbers2 = arrNames.stream().map(str->str.length()).collect(Collectors.toList());
        arrEvenNumbers2.stream().forEach(System.out::println);
    }

    Output

    Collect Even Nos in list
2
4
6
Length of Elements
4
6
5
3
  10. Find the Sum of Nos in List? 
    

    11. 

  11. Find the Sum of Nos in List?

    

    12. 

  12. Find the Sum of Nos in List?

    

    13. 


	


	
	
	

		
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