Check if Object fields already exists in another instance

I'm creating multiple instances of the same object and I want to check two fields to know if it has duplicates.

public class Professor {
    String name;
    String surName;
    String department;

    // Contructors, Setter and Getters
}

public class DProf {
    String depName;
    private static List<Professor> professors = new ArrayList<>();

    // Contructors, Setter and Getters

    public void addProfessor(Professor professor) {
        if (containsName(professor.name) && containsSurName(professor.surName)) {
            return;
        } else {
            professors.add(professor);
            new Professor(professor);
        }
    }

    public boolean containsName(final String name) {
        return professors.stream().anyMatch(o -> o.getName().equals(name));
    }

    public boolean containsSurName(final String surName) {
        return professors.stream().anyMatch(o -> o.getSurName().equals(surName));
    }
}

Edit: current approach with Professors being stored in List<Professors> and two methods cheking if namd and surname exist

I assume your DProf class also contains a List of Professors.

Interface java.util.List declares method contains(Object). The method returns true if the method argument equals one of the objects in the list. Method equals(Object), in class java.lang.Object is used to determine whether two objects are equal. Since all classes in java extend class Object, that means that your Professor class inherits that method. The implementation of method equals(Object) in class Object is a generic implementation and therefore not suitable for your Professor class. Hence you need to override method equals(Object) in class Professor.

Here is my modified version of class Professor.

public class Professor {
    private String name;
    private String surName;
    private String department;

    public Professor(String name, String surName) {
        this(name, surName, null);
    }

    public Professor(String name, String surName, String department) {
        this.name = name;
        this.surName = surName;
        this.department = department;
    }

    public void setDepartment(String dept) {
        department = dept;
    }

    @Override
    public boolean equals(Object obj) {
        boolean areEqual = false;
        if (obj instanceof Professor) {
            Professor other = (Professor) obj;
            areEqual = name.equals(other.name) &&  surName.equals(other.surName);
        }
        return areEqual;
    }
}

As you requested, method equals(), in class Professor, returns true if both Professor instances have the same name and surName.

Since the code in your question is not a minimal, reproducible example I made some assumptions regarding the code. Here is my modified version of your DProf class. See notes after the code.

import java.util.ArrayList;
import java.util.List;
import java.util.Objects;

public class DProf {
    private List<Professor> professors;
    String depName;

    public DProf(String name) {
        Objects.requireNonNull(name, "Null department name");
        depName = name;
        professors = new ArrayList<Professor>(); // create an empty list of professors
    }

    public void addProfessor(Professor professor) {
        // Here I want to check if new Professor instance name and surname already exist in another instance of the object
        if (!professors.contains(professor)) {
            professor.setDepartment(depName);
            professors.add(professor);
        }
    }

    public static void main(String[] args) {
        DProf magic = new DProf("Sorcery");
        Professor prof = new Professor("Cuthbert", "Binns");
        magic.addProfessor(prof);
        prof = new Professor("Charity", "Burbage");
        magic.addProfessor(prof);
        prof = new Professor("Albus", "Dumbledore");
        magic.addProfessor(prof);
    }
}

I added a member professors since I assume that a department has a number of different professors associated with it. I assume that initially, a professor is not associated with a department until you call the addProfessor() method. Hence I also set the Professor's department in the addProfessor() method. I also added a main() method simply to allow me to test run the code to make sure it runs successfully.

you can make a static private field like this :

private static list<String> field = new ArrayList();

and before you add a Professor you can check field.contains(name)

but i think some better pattern must exist

edit: and add the name in your list when you call the constructor of Professor

You could add a equals() method in Professor class.

@Override
public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null || getClass() != o.getClass()) return false;
    Professor professor = (Professor) o;
    return Objects.equals(name, professor.name) &&
            Objects.equals(surName, professor.surName) &&
            Objects.equals(department, professor.department);
}

Then you could initialize a List inside DProf class and add each Professor object you create inside it.

class DProf {
    static List<Professor> profList = new ArrayList<>();

    public boolean addProfessor(Professor professor) {
        for (Professor someProf : profList) {
            if (professor.equals(someProf)) return false;
        }
        profList.add(professor);
        return true;
    }
}

This way you could check whether each Professor object matches with already existing objects.