Why use get and set in Java?

The use of get and set methods is practiced for security reasons. The method applied in this case is encapsulation. The goal in fact is not to allow variables to be modified directly. For example, let's imagine the following possible class structure:

public class Ponto {
    public int x;
    public int y;

    public Ponto(){}

   // métodos da classe.
}

From the moment you instantiate the point object, you have direct access to the variables x and y. The most common thing to do in these cases is to change the visibility of the variable, usually using "private "instead of"public". Soon after comes the adorable gets and sets. With the use of the gets and sets you start to allow a private visibility variable to be accessed. Let's go to another example:

public class Ponto {
    private int x;
    private int y;

    public Ponto(){}

    public int setX(int valor){
       this.x = valor;
    }

    public int getX(){
       return this.x;
    }


   // métodos da classe.
}

In the example above, only through the methods getX and setX is it possible to manipulate the variable X, while the variable Y because it does not have get and set cannot be accessed directly. Now the most important part. it makes no sense to create classes with variables of private visibility if you are going to create for all of them (variables) the get and set. Now, if the purpose of private is to make access impossible, what sense does it make to use get and set if they give direct access to the variable? But why do we actually use it? simple, by standardization, but we must use in a moderate way. For the reasons already mentioned.

Hug.

Being short and thick... If all your accessor get does is return a field from the class, and all your accessor set does is change the value of that field, type like this:

public class Pessoa {
    private int _idade;

    public int getIdade() { return _idade; }
    public void setIdade(value) { _idade = value; }
}

...Maybe you should make your camp public.

This does not give any security. If there is performance consideration, it is because your execution stack gets one level higher to handle the value of the age variable.

Another security consideration is that there is a programming called reflection . I leave it to you to research on this, but in summary: making a variable private does not mean that it cannot be read or changed directly by other classes. You just made these operations more expensive in terms of processing.

Accessors are methods and as such serve to execute some logic that is of interest to you. For example, assuming you have a property by reference, such as a list. Let's give our class Person A list of children:

public class Pessoa {
    public List<Pessoa> filhos;
}

If you try to access this property on an instance, you may receive a NULL pointer error.

Pessoa p = new Pessoa();
p.filhos.Add(new Pessoa()); // você acessou uma variável nula.

Now let's make a really useful accessory. Please assure the user of our API that they will be able to access a guaranteed instantiated list, as follows:

public class Pessoa {
    private List<Pessoa> _filhos;
    public List<Pessoa> getFilhos() {
        if (this._filhos == null) {
            this._filhos = new List<Pessoa>();
        }
        return this._filhos;
    }
}

Now this will never give null pointer error:

Pessoa p = new Pessoa();
p.getFilhos.Add(new Pessoa());

The idea behind the accessors is this: a series of operations required to read or write values for the class is encapsulated in them.

The security of accessors therefore depends on what is implemented in them. In cases like the example I used, the security is in avoiding a NULL pointer exception. Other security aspects may involve checking permissions, preventing divisions by zero, ensuring that file access will not cause lock in those files, etc.