Example on how to do dynamic variable binding in Java

Dynamic.java

package dynamic;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.HashMap;

/**
 * Console example application. 
 * 
 * For a proof of concept for dynamic assignment.
 */
public class Dynamic {

    /**
     * The "dynamic" variable map. We add variables in it. They key is the
     * variable name and the value is the variable content.
     */
    HashMap<String, String> vars = new HashMap<String, String>();

    /**
     * Main routine to start the dynamic example console app
     */
    public static void main(String[] args) throws IOException {
        // Creates object of this class and runs it
        new Dynamic().run();
    }

    /**
     * The app main method
     * 
     * @throws IOException 
     *              because of the readers may throw an exception sometimes
     */
    private void run() throws IOException {
        // Make buffered reader, (easy to handle strings with newlines)
        BufferedReader in = new BufferedReader(new InputStreamReader(System.in));

        // Helpful message
        System.out.println("To quit type \"quit\" or \"exit\".");
        System.out.println("To assign type \"variable name = value\"");
        System.out.println("To view the assignment type in the variable name");

        // Starting input, empty string
        String input = "";

        // While the app is not quitting, handle the line and then get next line
        while (!input.equals("quit") && !input.equals("exit")) {
            handleLine(input);
            System.out.print("> ");
            input = in.readLine();
        }
    }

    /**
     * Method that handles the line
     * 
     * @param input 
     *   the input from console to handle
     */
    private void handleLine(final String input) {
        // Guard statement if the string is empty or null just jump out
        if (input == null || input.length() == 0) {
            return;
        }
        // If input has an assignment, assign it to the vars map
        if (input.contains("=")) {
            // Cheap way to handle the assignment by splitting the string
            // and trimming the splits
            String[] split = input.split("=");
            String key = split[0].trim(); // Right of = is variable name
            String value = split[1].trim(); // Left of = is the value
            this.vars.put(key, value);
            
            // output what has been stored
            System.out.println("Stored " + value + " in " + key);    
        } 
        // If input is a string, assume it's a "variable name" key so output 
        // the variable
        else {
            String key = input.trim();
            System.out.println(key + ": " + vars.get(key));
        }
    }
}