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public abstract class AutoMap<K extends Comparable, V> extends TreeMap<K, V> { protected abstract V createValue(); public V getOrCreate(K key) { V value = get(key); if (value == null) { value = createValue(); put(key, value); } return value; } } public class MapOfMaps<J extends Comparable, K extends Comparable, V> extends AutoMap<J, Map<K, V>> { protected Map<K, V> createValue() { return new TreeMap<K, V>(); } } |
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