Question

I have some abstract class, in one of its method I use a string field which is supposed to be specific to the subclasses. I wonder what is the bect practice to implemnet this? via field and setting the field value in a consructors of the subclasses? via a static field and changing the value in every subclass?

What would you suggest?

Answer 1

The subclasses should specify the value. The superclass should define it’s interface. Use the template method design pattern.

Example:

public abstract class SuperClass {
  public abstract String getSomeValue();

  public void method() {
     String s = getSomeValue();
  }
}


public class SubClass extends SuperClass {
  private static final String CONSTANT = "";

  public String getSomeValue() {
    return CONSTANT;
  }
}

Another option is to set it in the constructor:

public abstract class SuperClass {
  private String value;

  public SuperClass(String value) {
    this.value = value;
  }
}


public class SubClass extends SuperClass {
  private static final String CONSTANT = "";

  public SubClass() {
    super(CONSTANT);
  }
}