java - How to force implementing a method of a class, without declaring the whole class abstract? -


i make base class (most time base class activity) extended other classes in project.

how can force clients implement method?

i cannot make 1 method abstract without making whole class abstract.

make class abstract. if want force implementation, you're not going want instatiate base class anyway. other methods can still have concrete implementations, follows;

public abstract class serverlisthtml extends httpservlet {     abstract public void foo();     public int concrete() {         return 0;     }  }

you can define own instantiable subclass if need basic "default" set of functionality.


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