Java vs. Scala example of callback implementation to animate on touch then do something when animation is finished (AndEngine SDK). I suggest that Java callback API and usage is boring because it requires a design pattern (Observer) and interfaces to define the API and classes to implement at all times...

java.java

// bad/lazy Java, too nested... should implement callback classes separately, but that also feels like overkill and leads to macaroni code
// other crap parts is that all interface methods needs implementation and ugly override annotations.
scene.setOnAreaTouchListener(new IOnAreaTouchListener() {
    @Override
    public boolean onAreaTouched(TouchEvent pSceneTouchEvent, ITouchArea pTouchArea, float pTouchAreaLocalX, float pTouchAreaLocalY) {
        if (pSceneTouchEvent.isActionDown()) {
            scene.registerEntityModifier(new DelayModifier(1.0f, new IEntityModifierListener() {
                @Override
                public void onModifierStarted(IModifier<IEntity> pModifier, IEntity pItem) {
                }
                @Override
                public void onModifierFinished(IModifier<IEntity> pModifier, IEntity pItem) {
                    ...
                }
            }));
        }
        return false;
    }
});

scala.scala

// "equivalent" Scala, but is ok code (IMO) because functions are first class
def onAreaTouch(pSceneTouchEvent: TouchEvent, pTouchArea: ITouchArea, pTouchAreaLocalX: Float,  pTouchAreaLocalY: Float) {
    if (pSceneTouchEvent.isActionDown) {
        def onFinished(pModifier: IModifier[IEntity], pItem: IEntity) {
            ...
        }
        val modifier = new DelayModifier(duration = 1.0f, onFinished = onFinished)
        scene.registerEntityModifier(modifier)
    }
}
scene.onAreaTouch(onAreaTouch)

Looks better using Scala, but it can be even better when the API you use is designed for Scala and not Java