Streams Demo

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Thu Jun 06 2024 02:40:22 GMT+0000 (Coordinated Universal Time)

Saved by @chatgpt #java

import java.util.*;

import java.util.stream.*;

public class StreamDemo {

    public static void main(String[] args) {

        ArrayList<Integer> al = new ArrayList<>();

        al.add(7);

        al.add(18);

        al.add(10);

        al.add(24);

        al.add(17);

        al.add(5);

        System.out.println("Actual List: " + al);

        Stream<Integer> stm = al.stream();  // get a stream; factory method

        Optional<Integer> least = stm.min(Integer::compare);   // Integer class implements Comparator [compare(obj1, obj2) static method]

        if(least.isPresent())

            System.out.println("Minimum integer: " + least.get());

        // min is a terminal operation, get the stream again

        /* 

        Optional<T> is a generic class packaged in java.util package.

        An Optional class instance can either contains a value of type T or is empty.

        Use method isPresent() to check if a value is present. Obtain the value by calling get() 

        */

        stm = al.stream();

        System.out.println("Available values: " + stm.count());

        stm = al.stream();

        Optional<Integer> higher = stm.max(Integer::compare);

        if(higher.isPresent())

            System.out.println("Maximum integer: " + higher.get());

        // max is a terminal operation, get stream again

        Stream<Integer> sortedStm = al.stream().sorted();    // sorted() is intermediate operation

        // here, we obtain a sorted stream

        System.out.print("Sorted stream: ");

        sortedStm.forEach(n -> System.out.print(n + " "));   // lambda expression

        System.out.println();

        /* 

        Consumer<T> is a generic functional interface declared in java.util.function

        Its abstract method is: void accept(T obj)

        The lambda expression in the call to forEach() provides the implementation of accept() method.

        */

        Stream<Integer> odds = al.stream().sorted().filter(n -> (n % 2) == 1);

        System.out.print("Odd values only: ");

        odds.forEach(n -> System.out.print(n + " "));

        System.out.println();

        /* 

        Predicate<T> is a generic functional interface defined in java.util.function

        and its abstract method is test(): boolean test(T obj)

        Returns true if object for test() satisfies the predicate and false otherwise.

        The lambda expression passed to the filter() implements this method.

        */

        odds = al.stream().sorted().filter(n -> (n % 2) == 1).filter(n -> n > 5);   // possible to chain the filters

        System.out.print("Odd values bigger than 5 only: ");

        odds.forEach(n -> System.out.print(n + " "));

        System.out.println();

    }

}

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