times.java

symbman（大学作业）

import java.util.Vector;


public class Times extends Expression {

private Expression[] factors;
	
	public Times(Expression[] f) {
		factors = new Expression[f.length];
		for(int i=0;i<f.length;i++)
			factors[i] = (Expression)f[i].clone();
	}
	
	public Expression[] getFactors() { return factors; }
	
	public Object clone() {
		return new Times(factors);
	}

	public Expression eval() {
		Expression[] result = new Expression[factors.length];
		for(int i=0;i<factors.length;i++)
			result[i] = factors[i].eval();
		return new Times(result);
	}

	public String toString() {
		StringBuffer result = new StringBuffer("(");
		result.append(factors[0].toString());
		for(int i=1;i<factors.length;i++) {
			result.append("*");
			result.append(factors[i].toString());
		}
		result.append(")");
			
		return result.toString();
	}
	
	public Expression derive(Symbol s) {
		
		Expression[] result = new Expression[factors.length];
		for(int i=0;i<factors.length;i++) {
			Expression[] partProd = new Expression[factors.length];
			for(int j=0;j<factors.length;j++) {
				partProd[j] = (i==j)?factors[j].derive(s):factors[j];
			}
			result[i] = new Times(partProd);
		}
		return new Plus(result);
	}
	
	public boolean equals(Expression ex) {
		if(!(ex instanceof Times)) return false;
		Times t = (Times)ex;
		Expression efac[] = t.getFactors();
		if(efac.length == factors.length) {
			boolean ret = true;
			for(int i=0;i<factors.length;i++)
				if(!(efac[i].equals(factors[i]))) {
					ret = false;
					//break;
				}
			return ret;
		}
		else return false;
	}
	
	public Expression simplify() {
		Vector v = new Vector();
		for(int i=0;i<factors.length;i++) {
			if((factors[i].simplify()).equals(new NumericValue(0.0)))
				return new NumericValue(0.0);
			if(!((factors[i].simplify()).equals(new NumericValue(1.0))))
				v.add(factors[i].simplify());
		}
			
		Expression simplFactors[] = new Expression[v.size()];
		for(int i=0;i<v.size();i++)
			simplFactors[i] = (Expression) v.get(i);
		
		return new Times(simplFactors);
			
	}

}