Question

我一直在研究这个问题，它涉及在java中实现马尔可夫链算法。当我为变量r赋值向量元素的值时，它给出了一个错误。（第54行）。错误显示“需要数组但找到了java.unit.Vector。”代码粘贴在下面。

import java.io.*;
import java.util.*;

class Chain {
    static final int NPREF = 2;    // size of prefix
    static final String NONWORD = "\n";
                    // "word" that can't appear
    Hashtable statetab = new Hashtable(); 
                    // key = Prefix, value = suffix Vector
    Prefix prefix = new Prefix(NPREF, NONWORD);
                    // initial prefix
    //Random rand = new Random();

// Chain build: build State table from input stream
void build(BufferedReader in) throws IOException
{
    StreamTokenizer st = new StreamTokenizer(in);

    st.resetSyntax();                     // remove default rules
    st.wordChars(0, Character.MAX_VALUE); // turn on all chars
    st.whitespaceChars(0, ' ');           // except up to blank
    while (st.nextToken() != st.TT_EOF)
        add(st.sval);
    add(NONWORD);
}

// Chain add: add word to suffix list, update prefix
void add(String word)
{
    Vector suf = (Vector) statetab.get(prefix);
    if (suf == null) {
        suf = new Vector();
        statetab.put(new Prefix(prefix), suf);
    }
    suf.addElement(word);
    prefix.pref.removeElementAt(0);
    prefix.pref.addElement(word);
}

// Chain generate: generate output words
void generate(int nwords, PrintWriter out, Vector <Integer> random_num)
{
    prefix = new Prefix(NPREF, NONWORD);
    for (int i = 0; i < nwords; i++) {
        Vector s = (Vector) statetab.get(prefix);
        if (s == null) {
            System.err.println("Markov: internal error: no state");
            System.exit(1);
        }

        final int r = (random_num.get(i) % s.size());
        String suf = (String) s.elementAt(r);
        if (suf.equals(NONWORD))
            break;
        out.println(suf);
        prefix.pref.removeElementAt(0);
        prefix.pref.addElement(suf);
    }
}
}

class Prefix {
    public Vector pref;    // NPREF adjacent words from input
static final int MULTIPLIER = 31;    // for hashCode()

// Prefix constructor: duplicate existing prefix
Prefix(Prefix p)
{
    pref = (Vector) p.pref.clone();
}

// Prefix constructor: n copies of str
Prefix(int n, String str)
{
    pref = new Vector();
    for (int i = 0; i < n; i++)
        pref.addElement(str);
}

// Prefix hashCode: generate hash from all prefix words
public int hashCode()
{
    int h = 0;

    for (int i = 0; i < pref.size(); i++)
        h = MULTIPLIER * h + pref.elementAt(i).hashCode();
    return h;
}

// Prefix equals: compare two prefixes for equal words
public boolean equals(Object o)
{
    Prefix p = (Prefix) o;

    for (int i = 0; i < pref.size(); i++)
        if (!pref.elementAt(i).equals(p.pref.elementAt(i)))
            return false;
    return true;
}

}

class Markov {
    static final int MAXGEN = 10000; // maximum words generated
        static Vector <Integer> random_num = new Vector <Integer>();

        static BufferedReader random_reader;
    public static void main(String[] args) throws IOException
    {            

                                 BufferedReader in = new BufferedReader (new FileReader ("../alice30.txt"));
                                 PrintWriter out = new PrintWriter (new FileWriter ("../output/markov_java_out.txt"));             
                                 BufferedReader random_reader = new BufferedReader (new FileReader ("../random_num.txt"));
                                 String s;
                                 s= random_reader.readLine();
                                 while(s != null)
                                 {
                                         int element = Integer.parseInt(s.trim());
                                         random_num.addElement(new Integer(element));
                                         s = random_reader.readLine();
                                 }

        Chain chain = new Chain();
        int nwords = MAXGEN;

        chain.build(in);

                in.close();
        chain.generate(nwords,out, random_num);
                out.close();
    }
}

Answer 1

您的意思是random_num.elementAt(i)吗？

Answer 2

试试这个：

import java.io.*;
import java.util.Hashtable;
import java.util.Vector;

class Chain
{
    static final int NPREF = 2; // size of prefix
    static final String NONWORD = "\n";
    // "word" that can't appear
    Hashtable statetab = new Hashtable();
    // key = Prefix, value = suffix Vector
    Prefix prefix = new Prefix(NPREF, NONWORD);
    // initial prefix
    //Random rand = new Random();

    // Chain build: build State table from input stream
    void build(BufferedReader in) throws IOException
    {
        StreamTokenizer st = new StreamTokenizer(in);

        st.resetSyntax();                     // remove default rules
        st.wordChars(0, Character.MAX_VALUE); // turn on all chars
        st.whitespaceChars(0, ' ');           // except up to blank
        while (st.nextToken() != st.TT_EOF)
        {
            add(st.sval);
        }
        add(NONWORD);
    }

    // Chain add: add word to suffix list, update prefix
    void add(String word)
    {
        Vector suf = (Vector) statetab.get(prefix);
        if (suf == null)
        {
            suf = new Vector();
            statetab.put(new Prefix(prefix), suf);
        }
        suf.addElement(word);
        prefix.pref.removeElementAt(0);
        prefix.pref.addElement(word);
    }

    // Chain generate: generate output words
    void generate(int nwords, PrintWriter out, Vector random_num)
    {
        prefix = new Prefix(NPREF, NONWORD);
        for (int i = 0; i < nwords; i++)
        {
            Vector s = (Vector) statetab.get(prefix);
            if (s == null)
            {
                System.err.println("Markov: internal error: no state");
                System.exit(1);
            }
            int r = ((Integer)random_num.get(i) % s.size());
            String suf = (String) s.elementAt(r);
            if (suf.equals(NONWORD))
            {
                break;
            }
            out.println(suf);
            prefix.pref.removeElementAt(0);
            prefix.pref.addElement(suf);
        }
    }
}

class Prefix
{
    public Vector pref; // NPREF adjacent words from input
    static final int MULTIPLIER = 31; // for hashCode()

    // Prefix constructor: duplicate existing prefix
    Prefix(Prefix p)
    {
        pref = (Vector) p.pref.clone();
    }

    // Prefix constructor: n copies of str
    Prefix(int n, String str)
    {
        pref = new Vector();
        for (int i = 0; i < n; i++)
        {
            pref.addElement(str);
        }
    }

    // Prefix hashCode: generate hash from all prefix words
    public int hashCode()
    {
        int h = 0;

        for (int i = 0; i < pref.size(); i++)
        {
            h = MULTIPLIER * h + pref.elementAt(i).hashCode();
        }
        return h;
    }

    // Prefix equals: compare two prefixes for equal words
    public boolean equals(Object o)
    {
        Prefix p = (Prefix) o;

        for (int i = 0; i < pref.size(); i++)
        {
            if (!pref.elementAt(i).equals(p.pref.elementAt(i)))
            {
                return false;
            }
        }
        return true;
    }

}

class Markov
{
    static final int MAXGEN = 10000; // maximum words generated
    static Vector random_num = new Vector();
    static BufferedReader random_reader;

    public static void main(String[] args) throws IOException
    {

        BufferedReader in = new BufferedReader(new FileReader("../alice30.txt"));
        PrintWriter out = new PrintWriter(new FileWriter("../output/markov_java_out.txt"));
        BufferedReader random_reader = new BufferedReader(new FileReader("../random_num.txt"));
        String s;
        s = random_reader.readLine();
        while (s != null)
        {
            int element = Integer.parseInt(s.trim());
            random_num.addElement(new Integer(element));
            s = random_reader.readLine();
        }

        Chain chain = new Chain();
        int nwords = MAXGEN;

        chain.build(in);

        in.close();
        chain.generate(nwords, out, random_num);
        out.close();
    }
}

我建议您尝试ArrayList<Integer>而不是Vector。

我无法运行您的代码，因为我没有像“alice30.txt”这样的文件，但是这个代码段运行正常如下：

import java.util.Arrays;
import java.util.List;
import java.util.Vector;

public class Junk
{

    public static void main(String[] args)
    {
        Vector random_num = new Vector()
        {{
            add(4);
            add(3);
            add(1);
        }};
        int i = 1;
        List<Integer> s = Arrays.asList(new Integer []{1, 2, 3, 4, 5});
        // The next line looks just like the one I gave you
        int r = ((Integer)random_num.get(i) % s.size());
        System.out.println(r);
    }
}

Answer 3

您粘贴的代码将无法编译，因为您在Vector上使用了数组语法。在马尔科夫声明Vector这样：

static Vector<Integer> random_num = new Vector<Integer>();

同时将参数更改为方法generate(...)以匹配，最后通过将random_num视为Vector而不是数组来修复此方法：

final int r = (random_num.get(i) % s.size());

作为旁注，我注意到你没有利用Java 5的能力来输入你的收藏。这可以防止显式铸造的需要，并且通常被认为是良好的做法。尝试像这样声明你的Hashtable：

Hashtable<Prefix, Vector<String>> statetab = new Hashtable<Prefix, Vector<String>>();

阅读this以供参考

这里的代码包含除了复制构造函数之外的一切，你需要多考虑一下：

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.io.StreamTokenizer;
import java.util.Hashtable;
import java.util.List;
import java.util.Vector;

class Chain {
    static final int NPREF = 2;
    static final String NONWORD = "\n";
    Hashtable<Prefix, Vector<String>> statetab = new Hashtable<Prefix, Vector<String>>();
    Prefix prefix = new Prefix(NPREF, NONWORD);

    void build(final BufferedReader in)
            throws IOException {
        final StreamTokenizer st = new StreamTokenizer(in);

        st.resetSyntax(); // remove default rules
        st.wordChars(0, Character.MAX_VALUE); // turn on all chars
        st.whitespaceChars(0, ' '); // except up to blank
        while (st.nextToken() != StreamTokenizer.TT_EOF) {
            add(st.sval);
        }
        add(NONWORD);
    }

    // Chain add: add word to suffix list, update prefix
    void add(final String word) {
        Vector<String> suf = this.statetab.get(this.prefix);
        if (suf == null) {
            suf = new Vector<String>();
            this.statetab.put(new Prefix(this.prefix), suf);
        }
        suf.addElement(word);
        this.prefix.pref.removeElementAt(0);
        this.prefix.pref.addElement(word);
    }

    // Chain generate: generate output words
    void generate(final int nwords, final PrintWriter out, final List<Integer> random_num) {
        this.prefix = new Prefix(NPREF, NONWORD);
        for (int i = 0; i < nwords; i++) {
            final Vector<String> s = this.statetab.get(this.prefix);
            if (s == null) {
                System.err.println("Markov: internal error: no state");
                System.exit(1);
            }
            final int r = (random_num.get(i) % s.size());
            final String suf = (String) s.elementAt(r);
            if (suf.equals(NONWORD)) {
                break;
            }
            out.println(suf);
            this.prefix.pref.removeElementAt(0);
            this.prefix.pref.addElement(suf);
        }
    }
}

class Prefix {
    public Vector<String> pref; // NPREF adjacent words from input
    static final int MULTIPLIER = 31; // for hashCode()

    // Prefix constructor: duplicate existing prefix
    Prefix(final Prefix p) {
        //this.pref = p.pref.clone();
    }

    // Prefix constructor: n copies of str
    Prefix(final int n, final String str) {
        this.pref = new Vector<String>();
        for (int i = 0; i < n; i++) {
            this.pref.addElement(str);
        }
    }

    // Prefix hashCode: generate hash from all prefix words
    @Override
    public int hashCode() {
        int h = 0;
        for (int i = 0; i < this.pref.size(); i++) {
            h = MULTIPLIER * h + this.pref.elementAt(i).hashCode();
        }
        return h;
    }

    // Prefix equals: compare two prefixes for equal words
    @Override
    public boolean equals(final Object o) {
        final Prefix p = (Prefix) o;
        for (int i = 0; i < this.pref.size(); i++) {
            if (!this.pref.elementAt(i).equals(p.pref.elementAt(i))) {
                return false;
            }
        }
        return true;
    }

}

public class Markov {
    static final int MAXGEN = 10000; // maximum words generated
    static List<Integer> random_num = new Vector<Integer>();
    static BufferedReader random_reader;

    public static void main(final String[] args)
            throws IOException {

        final BufferedReader in = new BufferedReader(new FileReader("../alice30.txt"));
        final PrintWriter out = new PrintWriter(new FileWriter("../output/markov_java_out.txt"));
        final BufferedReader random_reader = new BufferedReader(new FileReader("../random_num.txt"));
        String s;
        s = random_reader.readLine();
        while (s != null) {
            final int element = Integer.parseInt(s.trim());
            random_num.add(new Integer(element));
            s = random_reader.readLine();
        }
        final Chain chain = new Chain();
        final int nwords = MAXGEN;
        chain.build(in);
        in.close();
        chain.generate(nwords, out, random_num);
        out.close();
    }
}

在java中使用Vectors

3 个答案: