Core java interview Questions You'll Most Likely Be Asked (Second Edition)

What is the output of the following code snippet?
Stream numbers = Stream.of(10,15,20,25);
boolean anyMatch = numbers.anyMatch(num–> num%2==0);
System.out.println(anyMatch);
Answer:
The code snippet above uses the anyMatch() method on the
Stream Interface. This method returns true if any of the elements
in the input Stream match the specified condition. In this case, it
checks if there is an even number in the input Stream. Since
there are even numbers in the Stream, the
anyMatch() method returns a true. So, this code prints the
following output:
true
What is the difference between a Stream and a Collection?
Answer:
There are several differences between a Stream and a
Collection. These are as follows:

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224.
Collections actually store the data. A stream on the other
hand does not store any data, it just performs some
operations on the underlying data
When you perform an operation on a Collection, the
Collection gets modified. When you perform an operation on a
Stream obtained on a Collection, the underlying Collection
does not get modified
A Collection can be modified after it is created. A Stream on
the other hand cannot be modified after it is constructed
You can traverse a Collection any number of times. However,
you can traverse a Stream only once. If you wish to traverse
over a Stream again it is not possible, you need to create a
new Stream from the underlying source and traverse it again
Suppose you have a List of String values. You want to
create a new List that eliminates the duplicates from the
original List and has the String values in uppercase. How
will you achieve this via Stream operations?
Answer:
The following code snippet demonstrates the above requirement:
List fruits =
Arrays.asList(“Apple”,”Mango”,“Banana”,”Apple”,
”Orange”, “Mango”,”Strawberry”); //Line 1
List uniqueFruits =
fruits.stream().distinct().map(str–>
str.toUpperCase()).collect(Collectors.toList()); //Line
2
uniqueFruits.forEach(str–>
System.out.println(str));//Line 3

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225.
This code first creates a List of String values called fruits at
Line 1. Line 2 first invokes the fruits.stream() which obtains
a Stream on the fruits List. It then invokes the distinct()
operation. The distinct() method returns a new Stream that
consists of only the distinct elements in the input Stream. Next, it
invokes the map() operation. The map() operation can be used
to transform a Stream. It accepts as parameter a Function
instance and applies the Function to each element in the
Stream. Here, a lambda expression is used to convert each
String in the Stream to uppercase. Finally, it invokes the
collect() method, passing in a Collector that converts the
Stream to a List. Line 3 then prints all the elements in the
uniqueFruits List. So, this code prints the following output:
APPLE
MANGO
BANANA
ORANGE
STRAWBERRY