CODEWITHSUNDEEP
javastatic-methods
user452306
user452306

Reputation: 179

Check if object with same properties exist - Static factory method

Using static factory method, I want to create objects (e.g. persons), but throw an error/exception if a person with the same criteria is being created.

I have 2 classes Person.java / Program.java (<-Main)

My static method is as follow:

public class Person{
  private String firstName;
  private String lastName;

  private Person(String firstName, String lastName){
    this.firstName = firstName;
    this.lastName = lastName;
  }
  public static Person fullName(String firstName, String lastName){
     /*if(firstName.equals(this.firstName)){
        System.out.println("Person already exists!");
     }else{
       return new Person(firstName,lastName);
     }*/
     return new Person(firstName, lastName);
  }
}

Now obviously the commented-out part wouldn't work because Person isn't instanciated, but I'm kind of lost about how I could go on.

And yes, I'm overriding equals and hashcode!

Upvotes: 0

Views: 269

Answers (1)

davidxxx
davidxxx

Reputation: 131466

To achieve it you should keep traces of all created instances in the Person class by using a static collection. Note that it may cause memory retention if you don't use weak references for them and these are only referenced by the collection defined in Person.

Then about the check of an existing Person, as you overrided equals() and hashCode(), you could create a new Person from the parameters and check whether it was already created.

public class Person{
  private String firstName;
  private String lastName;

  private static Set<Person> persons = new HashSet<>();

  private Person(String firstName, String lastName){
    this.firstName = firstName;
    this.lastName = lastName;
  }

  // equals and hashCode overrided relying on firstName and lastName fields
  //   ..

  // Aditionnally to ease the creation of the exception message, override toString() too
  @Override
  public String toString(){
      return "name=" + name +", lastName=" + lastName);
  }

  public static Person fullName(String firstName, String lastName){
     Person p = new Person(firstName, lastName);
     if (persons.contains(p)){
       throw IllegalArgumentException("person " + p " already created";
     }
     persons.add(p);
     return p;
  }

}

Upvotes: 1

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