[FIXED] How to filter nested streams in Java 8 with lambda productions

Issue

I am trying to filter my Deals based on my Deal options but when I try to filter the code I get a type mismatch error that Set<DealOptions> cannot be converted to boolean. I want to keep the deals when all the deal options are red.

Here is my code:

import java.util.*;
import java.util.stream.Collectors;

class Deal {
    String dealname;
    String dealprice;
    Set<DealOptions> dealop;

    public String getDealname() {
        return dealname;
    }

    public void setDealname(String dealname) {
        this.dealname = dealname;
    }

    public String getDealprice() {
        return dealprice;
    }

    public void setDealprice(String dealprice) {
        this.dealprice = dealprice;
    }

    public Set<DealOptions> getDealop() {
        return dealop;
    }

    public void setDealop(Set<DealOptions> dealop) {
        this.dealop = dealop;
    }

}

class DealOptions {
    String optname;
    String color;

    public String getOptname() {
        return optname;
    }

    public void setOptname(String optname) {
        this.optname = optname;
    }

    public String getColor() {
        return color;
    }

    public void setColor(String color) {
        this.color = color;
    }

}

public class Test {

    public static void main(String[] args) 
             {

        Deal s = new Deal();
        Set<DealOptions> ops = new HashSet<DealOptions>();
        DealOptions op = new DealOptions();
        s.setDealname("mongo");
        s.setDealprice("500");

        op = new DealOptions();
        op.setColor("red");
        op.setOptname("redop");

        ops.add(op);
        op = new DealOptions();
        op.setColor("blue");
        op.setOptname("blueop");

        ops.add(op);
        op = new DealOptions();
        op.setColor("green");
        op.setOptname("greenop");

        ops.add(op);

        s.setDealop(ops);

        List<Deal> dl = new ArrayList<Deal>();

        dl.add(s);
        ops = new HashSet<DealOptions>();
        s = new Deal();
        op = new DealOptions();
        s.setDealname("test2");
        s.setDealprice("200");

        op = new DealOptions();
        op.setColor("indigo");
        op.setOptname("indigop");

        ops.add(op);
        op = new DealOptions();
        op.setColor("violet");
        op.setOptname("violetop");

        ops.add(op);
        op = new DealOptions();
        op.setColor("orange");
        op.setOptname("orangeop");

        ops.add(op);

        s.setDealop(ops);

        dl.add(s);

        List<Deal> dev = dl.stream().filter(
                (p) -> p.getDealop().stream().filter((po) -> po.getColor().equals("red")).collect(Collectors.toSet()))
                .collect(Collectors.toList()); // error here

    }
}

Error:

Cannot convert from Set to boolean

How do rectify this error how can I filter my deals based on my deal options?

Solution

You can use allMatch(predicate) to determine if all deals of an option are red:

Returns whether all elements of this stream match the provided predicate.

In this case, the predicate simply tells whether an option is red or not.

List<Deal> output =
    dl.stream()
      .filter(d -> d.getDealop().stream().allMatch(po -> po.getColor().equals("red")))
      .collect(Collectors.toList());

Answered By - Tunaki

Answer Checked By - Katrina (PHPFixing Volunteer)