Exp.java

package simulator;

import java.util.ArrayList;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;

public class Exp {

	private String exp;// stores expression (f(x)) which is in terms of y = f(x)
						// and objective fun (f(x,y)) in terms of z = f(x,y)

	// if expression is y=f(x), isfx flag is set true
	// if expression is x=f(y), isfx flag is set false
	private Boolean isfx = true;

	// if expression is objective fun, then isObj flag is set true
	// otherwise false
	private Boolean isObjFun = false;

	private String operator;

	// get expression
	public String getExp() {
		return exp;
	}

	// initialize exp and isfx
	public void setExp(String exp, Boolean isfx, Boolean isObjFun, String operator) {
		this.exp = exp;
		this.isfx = isfx;
		this.isObjFun = isObjFun;
		if (isObjFun)
			this.operator = "";
		else
			this.operator = operator;
	}

	@Override
	public String toString() {
		return this.exp;
	}

	/*
	 * Expression is a String. To evaluate such an expression we use javascript
	 * engine from ScriptEngine Library
	 */
	private ScriptEngineManager mgr = new ScriptEngineManager();
	private ScriptEngine engine = mgr.getEngineByName("JavaScript");

	// addValue() gives value to a variable in the expression
	// key = variable in expression
	// value = its value
	public void addValue(String key, Object value) {
		engine.put(key, value);
	}

	public Boolean getisfxFlag() {
		return this.isfx;
	}

	public Boolean followsOperator(double val1, String op, double val2) {
		Boolean ret = false;
		switch (op) {
		case "<":
			if (val1 < val2)
				ret = true;
			break;
		case "<=":
			if (val1 <= val2)
				ret = true;
			break;
		case ">":
			if (val1 > val2)
				ret = true;
			break;
		case ">=":
			if (val1 >= val2)
				ret = true;
			break;
		case "==":
			if (val1 == val2)
				ret = true;
			break;
		case "!=":
			if (val1 != val2)
				ret = true;
			break;
		case "=":
			if (val1 == val2)
				ret = true;
			break;
		default:
			ret = false;
		}
		return ret;
	}

	public Boolean getisObjFunFlag() {
		return this.isObjFun;
	}

	public Boolean satisfy(double x, double y) {
		if (isfx) {
			this.addValue("x", x);

			if (followsOperator(y, operator, this.solve()))
				return true;
			else
				return false;
		} else {
			this.addValue("y", y);
			// System.out.println(this.exp+":"+x+","+y+"="+this.solve());
			if (followsOperator(x, operator, this.solve()))
				return true;
			else
				return false;
		}

	}

	public ArrayList<SimplePoint> getCoordsSet(double limitX, double limitY, double step) {
		if (!isObjFun) {
			ArrayList<SimplePoint> coordsSet = new ArrayList<SimplePoint>();
			for (double i = 0; i < limitX; i += step) {
				if (isfx) {
					this.addValue("x", i);
					SimplePoint sp = new SimplePoint();
					sp.x = i;
					sp.y = this.solve();
					if (sp.y <= limitY)
						coordsSet.add(sp);
				} else {
					this.addValue("y", i);
					SimplePoint sp = new SimplePoint();
					sp.x = this.solve();
					sp.y = i;
					if (sp.x <= limitX)
						coordsSet.add(sp);
				}
			}
			return coordsSet;
		} else
			return null;
	}

	public double solve(double x, double y) {
		if (isObjFun) {
			this.addValue("x", x);
			this.addValue("y", y);
			return this.solve();
		} else
			return 0;
	}

	// return double value of expression after substituting all key with value
	// obtained from addValue() method
	public double solve() {
		try {

			Object res = engine.eval(exp);
			if (res instanceof Integer) {
				return (double) ((Integer) res).intValue();
			} else
				return (double) res;
		} catch (ScriptException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
			return 0;
		}
	}

}