Add array from list into a new set in Java

Question

I want to get the model numbers from the list only

['brand: Samsung, model number: VA2210-MH, size: 21.5', 'brand: Philipe, model number: 244E1SB, size: 21.5']

And I set create attributes and getter and setter of all attributes(only model number will be shown) in Monitor

public class Monitor{

    public String brand;
    public String modelNumber;
    public double size;


    public Monitor(String brand, String modelNumber, double size){
        this.brand = brand;
        this.modelNumber = modelNumber;
        this.size = size;
    }

    public void setModelNumber(String amodelNumber){
        modelNumber = amodelNumber;
    }

    public String getModelNumber(){
        return modelNumber;
    }
}

so I create a list and add the information into the list and a method to create a set with model number by the method modelNumberSet()

    import java.util.*; 

public class ComputerShop{


    private List<Monitor> monitorList = new ArrayList<>();


    public void addMonitor(String brand, String modelNumber, double size){
        Monitor newMonitor = new Monitor(brand, modelNumber, size);
        monitorList.add(newMonitor);
    }

    public Set<Monitor> modelNumberSet(){

        Set<Monitor> NewSet = new HashSet<>();


        for (Monitor m : monitorList) {
           NewSet.add(m.getModelNumber());
        }

        return NewSet;
    }
}

I hope the model number will be added into a new set, the output looks like

[VA2210-MH, 244E1SB]

So I use for loop to incase I will add more information in the future, but the error comes out when I use add(). Why the array cannot be added into the new set? Am I using the wrong function? Is there a better solution I should use?

Change Set<Monitor> to set<String> . You are adding model numbers to the set and their types are string. — Marwa Eldawy
– Marwa Eldawy, Commented Nov 24, 2019 at 17:06
Follow Java naming conventions. Variables such as NewSet should start with a lowercase letter, newSet. Even better would be using a meaningful name rather than generic “newSet”. — Basil Bourque
– Basil Bourque, Commented Nov 24, 2019 at 17:07

Basil Bourque · Accepted Answer · 2019-11-24 17:26:19Z

1

Change Set<Monitor> to Set<String>. You are adding model numbers to the set and their types are String. You are trying to put a String where a Monitor is expected. Square peg in a round hole.

Fix the modelNumberSet() method as follows:

    public Set<String> modelNumberSet(){
        Set<String> newSet = new HashSet<>();

        for (Monitor m : monitorList) {
            newSet.add(m.getModelNumber());
        }

        return newSet;
    }

edited Nov 24, 2019 at 17:26

Basil Bourque

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answered Nov 24, 2019 at 17:06

Marwa Eldawy

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2 Comments

PAK KIN HON Over a year ago

than you very much

Marwa Eldawy Over a year ago

@PAKKINHON Sure, if this answers your question, please mark it as the correct answer.

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