java集合操作

package Sets;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
import java.util.TreeSet;

/**
 * java集合操作
 * 
 * @author baby69yy2000
 * 
 */
public class Sets {

	/** 求并集 */
	public static <T> Set<T> union(Set<T> setA, Set<T> setB) {
		Set<T> setUnion;

		if (setA instanceof TreeSet)
			setUnion = new TreeSet<T>();
		else
			setUnion = new HashSet<T>();

		Iterator<T> iterA = setA.iterator();
		while (iterA.hasNext())
			setUnion.add(iterA.next());

		Iterator<T> iterB = setB.iterator();
		while (iterB.hasNext())
			setUnion.add(iterB.next());
		return setUnion;
	}

	/** 求交集 */
	public static <T> Set<T> intersection(Set<T> setA, Set<T> setB) {
		Set<T> setIntersection;
		T item;

		if (setA instanceof TreeSet)
			setIntersection = new TreeSet<T>();
		else
			setIntersection = new HashSet<T>();

		Iterator<T> iterA = setA.iterator();
		while (iterA.hasNext()) {
			item = iterA.next();
			if (setB.contains(item))
				setIntersection.add(item);
		}
		return setIntersection;
	}

	/** 求差集 */
	public static <T> Set<T> difference(Set<T> setA, Set<T> setB) {
		Set<T> setDifference;
		T item;

		if (setA instanceof TreeSet)
			setDifference = new TreeSet<T>();
		else
			setDifference = new HashSet<T>();

		Iterator<T> iterA = setA.iterator();
		while (iterA.hasNext()) {
			item = iterA.next();
			if (!setB.contains(item))
				setDifference.add(item);
		}
		return setDifference;
	}

	/**
	 * 判断子集操作 判断setA中的每个元素是否也存在于setB中
	 */
	public static <T> boolean subset(Set<T> setA, Set<T> setB) {
		return intersection(setA, setB).size() == setA.size();
	}

	/********************************下面是有序集的操作********************************/
	
	/** 求交集 */
	public static <T extends Comparable<? super T>> TreeSet<T> orderedIntersection(
			Set<T> a, Set<T> b) {
		TreeSet<T> setIntersection = new TreeSet<T>();
		Iterator<T> iterA = a.iterator(),
					iterB = b.iterator();
		T valueA, valueB;
		
		valueA = advance(iterA);
		valueB = advance(iterB);
		while(valueA != null && valueB != null) {
			if(valueA.compareTo(valueB) < 0)
				valueA = advance(iterA);
			else if(valueB.compareTo(valueA) < 0)
				valueB = advance(iterB);
			else {
				setIntersection.add(valueA);
				valueA = advance(iterA);
				valueB = advance(iterB);
			}
		}
		return setIntersection;
	}
	
	private static <T> T advance(Iterator<T> iter) {
		T value = null;
		if (iter.hasNext())
			value = iter.next();
		return value;
	}
}

评论

1 楼 nickevin 2009-06-24  

/** 求差集 */
public static <T> Set<T> difference(Set<T> setA, Set<T> setB) {
Set<T> setDifference;
T item;

if (setA instanceof TreeSet) {
setDifference = new TreeSet<T>();
} else {
setDifference = new HashSet<T>();
}

               // 判断一下集合的数量大小 再比较
if (setA.size() > setB.size()) {
Iterator<T> iterA = setA.iterator();
while (iterA.hasNext()) {
item = iterA.next();
if (!setB.contains(item)) {
setDifference.add(item);
}
}
} else {
Iterator<T> iterB = setB.iterator();
while (iterB.hasNext()) {
item = iterB.next();
if (!setA.contains(item)) {
setDifference.add(item);
}
}
}

return setDifference;
}