Bisection.java

/**
 * Java implementation of the Bisection method for solving equations.
 * 
 * @author samuel
 */
public class Bisection {
	
	private static final float TOLORANCE = (float) 0.001;
	
	/**
	 * Recursively determines the root for a given function
	 * between two intervals
	 * 
	 * <p>
	 * NOTE: This treats the <code>left</code> parameter as a lower bound and <code>right</code>
	 *       parameter as an upper bound; this means <code>left</code> should be smaller than 
	 *       <code>right</code>.
	 * @param left the first interval
	 * @param right the second interval
	 * @return the root for the function
	 */
	public static double bisect(double left, double right) {
		// Check if we have a valid intervals
		if (function(right) * function(left) >= 0) {
			// Interval not compliate to function
			// fail
			throw new IllegalArgumentException("Intervals don't fit in function");
		}
		double mid = (left + right) / 2;
		
		// Soft check if middle point is root
		if (function(mid) == 0.0) {
			return mid;
		}
		// Decide intervals for next iteration
		if (function(right) * function(mid) < 0 && canMoveOn(mid, right)) {
			return bisect(mid, right);
		} else if (canMoveOn(left, mid)) {
			return bisect(left, mid);
		} else {
			return mid;
		}
	}
	
	/**
	 * The function that drives the bisection
	 * 
	 * @param x
	 * @return
	 */
	public static double function(double x) {
		return x*x*x - x*x + 2;
	}
	
	/**
	 * Helper method for {@link #bisect} that determines whether the next iteration is 
	 * appropriate depending on the current intervals
	 * 
	 * @param left lower bound
	 * @param right upper bound
	 * @return <code>true</code> if can move on
	 */
	private static boolean canMoveOn(double left, double right) {
		return (right - left) >= TOLORANCE;
	}
	
	/**
	 * Run program
	 */
	public static void main(String[] args) {
		double root = bisect(-200, 300);
		System.out.printf("Root is: %.4f", root);
	}
}

nice though i have tested it and works better with a tolerance of 0.001

private static final float TOLORANCE = (float) 0.001;

private static final float TOLORANCE = (float) 0.001;

Nice catch Herman, I have updated the gist :)