Retrieve key by value in Hashtable

Question

Hello everyone,
I am wondering what is the most effective approach of retrieving key by value in a Java build-in Hashtable. Can anyone provide sample source codes?
Thanks in advance,
George

Answer 1

there is something I want to ask about hashtable also , please see this source code
import java.io.*;
import javagently.*;
public class Students
    static final int nMarks = 6;
    String name = "";
    int marks[] = new int[nMarks];
    int finalMark = 0;
    int weights[] = { 5 , 10, 5, 15, 15, 50 };
    void setMarks(BufferedReader in) throws IOException
        for(int i = 0 ; i < nMarks ; i++)
            marks[i] = Text.readInt(in);
    void setName(BufferedReader in) throws IOException
        name = Text.readString(in) + " " + Text.readString(in);
    void calculateFinal()
        for(int i = 0 ; i < nMarks ; i ++)
            finalMark += marks[i] + weights;
finalMark = finalMark / 100;
import java.io.*;
import java.util.*;
import javagently.*;
public class Marker
    public static void main(String args[]) throws IOException
        BufferedReader in = Text.open(System.in);
        BufferedReader fin = Text.open("C:\\brandnew\\marks.txt");
        Hashtable table = new Hashtable(10);
        for(int i = 0; i < 4 ; i++)
            Students student = new Students();
            student.setName(fin);
            student.setMarks(fin);
            student.calculateFinal();
            table.put(student.name, new Integer(student.finalMark));
        System.out.println("In the table are ");
        for(Enumeration e = table.keys(); e.hasMoreElements();)
            String name = (String)e.nextElement();
            System.out.println(name);
        while(true)
            try
                System.out.print("Whose mark do you want to know? ");
                String s = Text.readString(in) + " " + Text.readString(in);
                if(table.containsKey(s))
                    Integer result = (Integer) table.get(s);
                    System.out.println(result.intValue());
                else
                    System.out.println("Sorry try again!!!");
            catch(EOFException e)
                break;
}Worry not for javagently, it is an extra package to simplify input and output... The problem I want to ask here is , I got error when trying to execute the code
java.io.EOFException
at javagently.Text.refresh(Text.java:116)
at javagently.Text.readString(Text.java:109)
at Students.setName(Students.java:23)
at Marker.main(Marker.java:18)
Exception in thread "main"
I checked the source code and there is nothing wrong...