Java 8 consumer, predicate and supplier with streams

Consumer functional interface

*Consumer <T> is an in-built functional interface introduced in java 8 consumer can be used in all contexts where an object needs to be consumed i.e taken as input, and a few operations are to be performed on the object without returning any results.

performs this operation on the give argument 

@param t the input argument 

void accept(T t);

public class ConsumerDemo {

    public static void main(String[] args) {
        /*
         * Consumer<Integer> consumer = t -> System.out.println("Printing  : " + t);
         * 
         * consumer.accept(10);
         */

        List<Integer> list1 = Arrays.asList(1, 2, 3, 4, 5);

        list1.stream().forEach(t -> System.out.println("print  : " + t));

    }
}

Predicate functional interface

This functional interface used for conditional check

where you think ,we can use these true/false returning functions in day to day programing we should choose predicacte

Evaluates this predicates on the given argument 

@param t the input argument

boolean test (T t);

EXAMPLE:-

public class PredicateDemo {

    public static void main(String[] args) {

        List<Integer> list1 = Arrays.asList(1, 2, 3, 4, 5);

        list1.stream().filter(t -> t % 2 == 0).forEach(t -> System.out.println("print  Even: " + t));
    }
}

Supplier functional interface

Supplier can be used in all context where there is no input but  an output is expected.

gets a result 

@return a result 

T get();

EXAMPLE:-

public class SupplierDemo {

    public static void main(String[] args) {

        List<String> list1 = Arrays.asList();

        System.out.println(list1.stream().findAny().orElseGet(() -> "Hi viewers"));
    }

Steams in java 

* Stream api is used to process the collection of objects 

A stream is a sequence of objects that supports various methods that can be pipelined to produce the desired outcome or result.

It is not a data structure as it takes input from the collections arrays or I/O  channels.

Stream doesn't change the original data structure, they only deliver the result as per the pipelined methods.

why we need stream?

1 functional programing

2 code reduce 

3 bulk operation

for Each method Example:-

public class ForEachDemo {

    // filter----> conditional check

    public static void main(String[] args) {

        List<String> list = new ArrayList<>();
        list.add("Murrit");
        list.add("john");
        list.add("piter");
        list.add("marek");
        list.add("mac");

        for (String s : list) {
            if (s.startsWith("m")) {
                System.out.println(s);
            }
        }

        list.stream().filter(t -> t.startsWith("m")).forEach(t -> System.out.println(t));

        Map<Integer, String> map = new HashMap<>();

        map.put(1, "a");
        map.put(2, "b");
        map.put(3, "c");
        map.put(4, "d");

        /*
         * map.forEach((key,value)->System.out.println(key+": "+value));*/
        
          map.entrySet().stream().filter(k->k.getKey()%2==0).forEach(obj->System.out.println(obj));
         

        /*
         * Consumer<String> consumer=(t)->System.out.println(t); for(String s1:list) {
         * consumer.accept(s1); }
         */

    }
}