CODEWITHSUNDEEP
javacollections
user3858442
user3858442

Reputation: 25

Java POJO collection attributes

I have a POJO something like the one mentioned below. Here I'm referring Set collection attribute in POJO1. I understand that set does not contain duplicate. Do I need to override equals() and hashCode() methods in POJO2? Using a Set here is not really going to helpful unless we override equals and hashCode methods? Please help me to understand little bit more on this context!

public class POJO1 {

        private String name;
        private Set<POJO2> pj2;

        public Company(){
            pj2 = new HashSet<>();
        }

        //setter and getter methods

    }

Upvotes: 0

Views: 940

Answers (2)

Ivan
Ivan

Reputation: 8758

Yes the only way for Java to understand which objects are duplicates is to call equals() method. Default implementation of equals() checks that references of two objects point to the same location in memory.

But depending on exact implementation of your Set you might need to override hashCode/equals or implement Comparable interface.

Since you put objects of POJO2 into HashSet you need to verride hashCodeequalsmethods inPOJO2` class.

Upvotes: 1

Vy Do
Vy Do

Reputation: 52626

You do like this

import java.util.Set;

public class POJO1 {

    private String name;
    private Set<POJO2> pojo2;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Set<POJO2> getPojo2() {
        return pojo2;
    }

    public void setPojo2(Set<POJO2> pojo2) {
        this.pojo2 = pojo2;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        POJO1 pojo1 = (POJO1) o;

        if (name != null ? !name.equals(pojo1.name) : pojo1.name != null) return false;
        return pojo2 != null ? pojo2.equals(pojo1.pojo2) : pojo1.pojo2 == null;
    }

    @Override
    public int hashCode() {
        int result = name != null ? name.hashCode() : 0;
        result = 31 * result + (pojo2 != null ? pojo2.hashCode() : 0);
        return result;
    }

}

Learn more at https://docs.oracle.com/javase/10/docs/api/java/lang/Object.html#equals(java.lang.Object)

Upvotes: 0

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