Same method for multiple classes that implement the same interface

Question

Sorry I really didn't know how to title the question, here's the problem...

I have an interface and multiple classes that implement the interface. The implementation of some of the methods in the interface are exactly the same in every implementing class. I feel like there should be a way to simplify this so I don't have to write the same code every time. Example:

public interface Foo {
    String getName();
}

public class FooImpl1 implements Foo {
    private String name = "foo name1";

    public String getName() {
        return name;
    }
}

public class FooImpl2 implements Foo {
    private String name = "foo name2";

    public String getName() {
        return name;
    }
}

So to break down..

1. is there a way to put the code for getName in one place and each class has it's own name variable?

2. is there a way to make getName static so I don't have to create a new instance

Have better ideas?

Answer 1

Use an abstract class and initialize the field in the constructor:

public abstract class Foo {

 protected String name;

 String getName() {
  return name;
 }
}

public class FooImpl1 extends Foo {

 public FooImpl1 () {
  name = "foo name1";
 }
}

public class FooImpl2 extends Foo {

 public FooImpl1 () {
  name = "foo name2";
 }
}

JB Nizlet pointed out that it would be cleaner to do something like this:

public abstract class Foo {

protected String name;

public Foo(String newName) {
    name = newName;
}

 String getName() {
  return name;
 }
}

And then call super("foo name 1") in the subclasses.

As @Peter Lawrey said, if you already have an interface or want one for some other reason:

public interface IFoo {
 String getName();
}

public abstract class Foo implements IFoo {

 protected String name;

 String getName() {
  return name;
 }
}

Answer 2

You could take a very simple approach:

public interface Foo {

    String getName();
}

public class Named implements Foo {

    String name;

    public String getName() {
        return name;
    }
}

public class FooImpl1 extends Named {
    {name = "foo name1";}
}

public class FooImpl2 extends Named {
    {name = "foo name2";}
}

Answer 3

It doesn't really work for getters like in your example, but since the question is more generic I think it's worth mentioning that with Java 8 you can define default methods in interfaces . So if you had something a bit more complex like:

public interface ComplexFoo {
    String getFirstName();
    String getLastName();

    String getFullName();
}

You do not have to repeat the getFullName implementation in every subclass, but can specify it in the interface:

public interface ComplexFoo {
    String getFirstName();
    String getLastName();

    default String getFullName() {
        return getFirstName() + " " + getLastName();
    }
}

The getters though still need repeating, since they access members that are not yet available in the interface:

public class FooImpl1 implements ComplexFoo {
    private String firstName = "foo";
    private String lastName = "name1;

    private String getFirstName() { return firstName; }
    private String getLastName() { return lastName; }
}

public class FooImpl2 implements ComplexFoo {
    private String firstName = "foo";
    private String lastName = "name2;

    private String getFirstName() { return firstName; }
    private String getLastName() { return lastName; }
}