Rockmaple Blog

用Scala写了一个简单的分词工具

起了个名叫做segcala, 地址 http://segcala.googlecode.com。

这几天对Scala比较感兴趣，看了一些资料，不过语言这东西光看不练还是没感觉，就写了这样一个分词程序。使用了Chih-Hao Tsai的mmseg分词算法。做为依赖注入的粉丝，程序里使用了google guice做为依赖注入容器。

Scala在JVM上的运行效率可以达到和Java差不多的程度。做为同时支持面向对象和函数式编程思想的语言，其强大的表达能力则是Java所忘尘莫及。

以mmseg算法中求一个chunk的自由语素度的代码为例，看看Scala如何使程序变得更加简捷和清晰：

Scala版：

def largestSumMorphemicFreedomDegreeRule(chunks: List[Chunk]): List[Chunk] = {
    val c = chunks.reduceLeft((c1, c2) => {if (c1.degreeOfMorphemicFreedom > c2.degreeOfMorphemicFreedom) c1 else c2})
    chunks.filter(chunk => (chunk.degreeOfMorphemicFreedom == c.degreeOfMorphemicFreedom))
}

再看看Java版（取自solo L的mmseg库）:

public class LSDMFOCWRule implements IRule {/* (non-Javadoc)
 * @see org.solol.mmseg.core.IRule#invoke()
 */
public final IChunk[] invoke(final IChunk[] chunks) {
    LSDMFOCWRuleComparator[] orderedChunks = new LSDMFOCWRuleComparator[chunks.length];

    for (int i = 0; i < chunks.length; i++) {
        orderedChunks[i] = new LSDMFOCWRuleComparator(chunks[i]);
    }

    Arrays.sort(orderedChunks);

    int index = 0;
    double degreeOfMorphemicFreedom = orderedChunks[index].getChunk().getDegreeOfMorphemicFreedom();

    List list = new ArrayList(1);
    list.add(orderedChunks[index].getChunk());

    index++;

    while (index < orderedChunks.length) {

        if (orderedChunks[index].getChunk().getDegreeOfMorphemicFreedom() == degreeOfMorphemicFreedom) {
            list.add(orderedChunks[index].getChunk());
        } else {
            break;
        }
        index++;
    }

    IChunk[] degreeOfMorphemicFreedomChunks = new IChunk[list.size()];
    list.toArray(degreeOfMorphemicFreedomChunks);

    return degreeOfMorphemicFreedomChunks;
}

static class LSDMFOCWRuleComparator implements Comparable {

    private IChunk chunk;

    public LSDMFOCWRuleComparator(IChunk chunk) {
        this.chunk = chunk;
    }

    public IChunk getChunk() {
        return chunk;
    }

    public int compareTo(Object obj) {
        IChunk another = ((LSDMFOCWRuleComparator) obj).getChunk();

        double temp = another.getDegreeOfMorphemicFreedom()
                - chunk.getDegreeOfMorphemicFreedom();

        if (temp > 0D) {
            return 1;
        } else if (temp < 0D) {
            return -1;
        } else {
            return 0;
        }
    }
}