countingmapdata5.java

JAVA编程思想第四版英文原版习题答案. pdf原版的

// containers/CountingMapData5.java
// TIJ4 Chapter Containers, Exercise 5, page 809
// Modify CountingMapData.java to fully implement the flyweight
// by adding a custom EntrySet class like the one in Countries.java.
// See also alternate solution CountingMapData5Alt.java. 
import java.util.*;
import net.mindview.util.*;
import static org.greggordon.tools.Print.*;

public class CountingMapData5 extends AbstractMap<Integer,String> {	
  	private static String[] chars =
    		"A B C D E F G H I J K L M N O P Q R S T U V W X Y Z"
    		.split(" ");
	static class Entry implements Map.Entry<Integer,String> {
    		int index;
    		Entry(int index) { this.index = index; }
    		public boolean equals(Object o) {
      			return Integer.valueOf(index).equals(o);
    		}
    		public Integer getKey() { return index; }
    		public String getValue() {
			return chars[index % chars.length] +
        			Integer.toString(index / chars.length);
    		}
    		public String setValue(String value) {
      			throw new UnsupportedOperationException();
    		}
    		public int hashCode() {
      			return Integer.valueOf(index).hashCode();
    		}
  	}
	// Use AbstractSet by implementing size() & iterator()
    	static class EntrySet extends AbstractSet<Map.Entry<Integer,String>> {
		private int size;
      		EntrySet(int size) {
			if(size < 0) this.size = 0;
			else this.size = size;
        	}
		public int size() { return size; }
		private class Iter implements Iterator<Map.Entry<Integer,String>> {
        		// Only one Entry object per Iterator:
        		private Entry entry = new Entry(-1);
        		public boolean hasNext() {
				return entry.index < size - 1;
        		}
        		public Map.Entry<Integer,String> next() {
				entry.index++;
          			return entry;
        		}
        		public void remove() {
          			throw new UnsupportedOperationException();
        		}
      		}
      		public Iterator<Map.Entry<Integer,String>> iterator() {
			return new Iter();
      		}			
	}
	private static Set<Map.Entry<Integer,String>> entries = 
		new EntrySet(chars.length);
	public Set<Map.Entry<Integer,String>> entrySet() { return entries; }
	static Map<Integer,String> select(final int size) {
    		return new CountingMapData5() {
      			public Set<Map.Entry<Integer,String>> entrySet() {
        			return new EntrySet(size);
      			}
    		};
  	}	
	public static void main(String[] args) {
		println(new CountingMapData5());
		println(select(10));
	}
}