/* Lab 5: Math Expression Factory 7/21/05 */

abstract class Expression {
	abstract int evaluate();
	abstract int positiveEvaluate();
}

class Number extends Expression {
	int value;

	Number(int value) {
		this.value = value;
	}

	// new Number(5).evaluate() == 5
	// Evaluate this Number
	int evaluate() {
		// ... this.value ...
		return this.value;
	}

	// new Number(-5).positiveEvaluate() == 5
	// new Number(5).positiveEvaluate() == 5
	// Fully evaluate this Number and make it positive
	int positiveEvaluate() {
		// ... this.value ...
		return new AbsoluteValue(new Number(this.value)).evaluate();
	}
}

class Plus extends Expression {
	Expression left;
	Expression right;

	Plus(Expression left, Expression right) {
		this.left = left;
		this.right = right;
	}

	// new Plus(new Plus(new Number(5), new Number(-2)), new Number(6)).evaluate() == 9
	// Evaluate this Plus expression fully 
	int evaluate() {
		// ... this.left.ExpressionMethod() ... this.right.ExpressionMethod() ...
		return this.left.evaluate() + this.right.evaluate();
	}

	// new Plus(new Plus(new Number(5), new Number(-12)), new Number(6)).positiveEvaluate() == 1 
	// new Plus(new Plus(new Number(5), new Number(-2)), new Number(6)).positiveEvaluate() == 9	
	// To determine the positive fully evaluated value of this Plus expression
	int positiveEvaluate() {
		return new AbsoluteValue(new Number(this.evaluate())).evaluate();
	}
}

class Minus extends Expression {
	Expression left;
	Expression right;

	Minus(Expression left, Expression right) {
		this.left = left;
		this.right = right;
	}

	// new Minus(new Plus(new Number(5), new Number(-2)), new Number(6)).evaluate() == -3
	// Evaluate this Minus expression fully 
	int evaluate() {
		// ... this.left.ExpressionMethod() ... this.right.ExpressionMethod() ...
		return this.left.evaluate() - this.right.evaluate();
	}

	// new Minus(new Plus(new Number(5), new Number(-2)), new Number(6)).positiveEvaluate() == 3	
	// To determine the positive fully evaluated value of this Minus expression
	int positiveEvaluate() {
		return new AbsoluteValue(new Number(this.evaluate())).evaluate();
	}
}

class AbsoluteValue extends Expression {
	Expression value;

	AbsoluteValue(Expression value) {
		this.value = value;
	}

	// new AbsoluteValue(new Minus(new Plus(new Number(5), 
	//			       new Number(-2)), 
	// 		     new Number(6))).evaluate() == 3
	// new AbsoluteValue(new Minus(new Plus(new Number(5), 
	//			       new Number(10)), 
	// 		     new Number(6))).evaluate() == 9
	// Evalute this AbsoluteValue expression fully
	int evaluate() {
		// ... this.value.ExpressionMethod() ...
		if (this.value.evaluate() < 0)
			return - this.value.evaluate(); 
				// unary minus, equivalent in effect to 0 - value.evaluate()
		else 
			return this.value.evaluate();
	}	

	// new AbsoluteValue(new Minus(new Plus(new Number(5), 
	//			       new Number(-2)), 
	// 		     new Number(6))).positiveEvaluate() == 3
	// new AbsoluteValue(new Minus(new Plus(new Number(5), 
	//			       new Number(10)), 
	// 		     new Number(6))).positiveEvaluate() == 9	
	// To determine the positive fully evaluated value of this AbsoluteValue expression	
	int positiveEvaluate() {
		return this.evaluate();
	}
}