When designing an abstract class, why should you avoid calling abstract methods inside its constructor?

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Utilisateur anonyme · Accepted Answer

This is a problem of initialization order. The subclass constructor will not have had a chance to run yet and there is no way to force it to run it before the parent class. Consider the following example class:

        public abstract class Widget {
	        private final int cachedWidth;
	        private final int cachedHeight;
	
	        public Widget() {
	            this.cachedWidth = width();
	            this.cachedHeight = height();
	        }
	
	        protected abstract int width();
	        protected abstract int height();
	    }

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