Methods Should Do Only One Thing

Summary

Methods should do only one thing.

Details

A useful guide as to whether a function is doing only one thing is given in “Clean Code” by Robert C Martin.

“another way to know that a function is doing more than “one thing” is if you can extract another function from it with a name that is not merely a restatement of its implementation.”

Bad

  1.   public void updateFooStatusAndRepository(Foo foo) {
  2.      if ( foo.hasFjord() ) {
  3.         this.repository(foo.getIdentifier(), this.collaborator.calculate(foo));
  4.      }
  6.      if (importantBusinessLogic()) {
  7.        foo.setStatus(FNAGLED);
  8.        this.collaborator.collectFnagledState(foo);
  9.      }
  10.   }

Better

  1.   public void registerFoo(Foo foo) {
  2.      handleFjords(foo);
  3.      updateFnagledState(foo);
  4.   }
  6.   private void handleFjords(Foo foo) {
  7.       if ( foo.hasFjord() ) {
  8.         this.repository(foo.getIdentifier(), this.collaborator.calculate(foo));
  9.      }
  10.   }
  12.   private void updateFnagledState(Foo foo) {
  13.     if (importantBusinessLogic()) {
  14.        foo.setStatus(FNAGLED);
  15.        this.collaborator.collectFnagledState(foo);
  16.      }
  17.   }

You’ve gone too far

  1.   public void registerFoo(Foo foo) {
  2.      handleFjords(foo);
  3.      updateFnagledState(foo);
  4.   }
  6.   private void handleFjords(Foo foo) {
  7.       if ( foo.hasFjord() ) {
  8.         this.repository(foo.getIdentifier(), this.collaborator.calculate(foo));
  9.      }
  10.   }
  12.   private void updateFnagledState(Foo foo) {
  13.     if (importantBusinessLogic()) {
  14.        updateFooStatus(foo);
  15.        this.collaborator.collectFnagledState(foo);
  16.      }
  17.   }
  19.   private void updateFooStatus(Foo foo) {
  20.     foo.setStatus(FNAGLED);
  21.   }