CODEWITHSUNDEEP
javadesign-patternscommand-pattern
Sha
Sha

Reputation: 1181

Implement Command Pattern Effectively

Initial code:

public void updateState(final int state)
{
    preSet();
    itsState = state;
    postSet();
}
public void setTitle(final String title)
{
    preSet();
    itsTitle = title;
    postSet();
}

After my Command Pattern Implementation:

public void updateState(final int state)
{
  CallableManager.doInTransaction(new Callable<Void>()
  {
     @Override
     public Void execute()
     {
       itsHiddenNodes = hiddenNodes;
       return null;
     }
  });
}
public void setTitle(final String title)
{
  CallableManager.doInTransaction(new Callable<Void>()
  {
     @Override
     public Void execute()
     {
       itsTitle = title;
       return null;
     }
  });
}

This interface is created for pass method as parameter.

private interface Callable<T>
{
    public T execute();
}

This class is created to manage command pattern.

private class CallableManager
{
    public <T> static void doInTransaction(final Callable<T> callable)
    {
        preSet();
        callable.execute();
        postSet();
    }
}

As you see, implementing command pattern does not look like very effective at least as line of code for this example. For this example, I implement command pattern to escape from repeated code and decrease the line of code. But as a result both of them are not provided for this example. Please give me some advice. How can I use command pattern effectively?

Upvotes: 2

Views: 280

Answers (1)

jaco0646
jaco0646

Reputation: 17066

A lambda can reduce the code duplication considerably. Also, Runnable seems like a more appropriate interface than Callable, since you are not returning a value.

public class MainJava {
    private int state;
    private String title;

    public static void main(String... args) {
        MainJava mj = new MainJava();
        mj.setState(42);
        mj.setTitle("My Title");
    }

    public void setState(int state) {
        doInTransaction(() -> this.state = state);
    }
    public void setTitle(String title) {
        doInTransaction(() -> this.title = title);
    }

    private void doInTransaction(Runnable runnable) {
        preSet();
        runnable.run();
        postSet();
    }

    private void preSet() {
        System.out.println("preset");
    }
    private void postSet() {
        System.out.println("post-set");
    }
}

Upvotes: 4

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