TextBlockMemoized.java

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 * PlantUML : a free UML diagram generator
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package net.sourceforge.plantuml.klimt.shape;

import net.sourceforge.plantuml.klimt.font.StringBounder;
import net.sourceforge.plantuml.klimt.geom.XDimension2D;

/**
 * Abstract base class for TextBlock implementations where
 * calculateDimension() is expensive. The result is memoized and
 * automatically invalidated when the StringBounder type changes.
 * <p>
 * Subclasses must implement {@link #calculateDimensionSlow(StringBounder)}
 * with the real computation. Callers use the standard
 * {@link #calculateDimension(StringBounder)} which is final and cached.
 */
public abstract class TextBlockMemoized implements TextBlock {

	private XDimension2D cachedDimension;
	private Class<? extends StringBounder> lastCaller;

	@Override
	public final XDimension2D calculateDimension(StringBounder stringBounder) {
		final Class<? extends StringBounder> currentCaller = stringBounder.getClass();
		if (cachedDimension == null || lastCaller != currentCaller) {
			cachedDimension = calculateDimensionSlow(stringBounder);
			lastCaller = currentCaller;
		}
		return cachedDimension;
	}

	protected abstract XDimension2D calculateDimensionSlow(StringBounder stringBounder);

	protected void invalidateDimensionCache() {
		cachedDimension = null;
		lastCaller = null;
	}

}