expression.java

symbman（大学作业）

public abstract class Expression implements Cloneable {
	
	public abstract Expression eval();
	
	public abstract String toString();
	
	public abstract Object clone();
	
	//public abstract boolean equals(Expression e);
	
	public abstract Expression derive(Symbol s);
	
	public abstract Expression simplify();
	
	public Expression recursiveEval() {
		Expression temp=this;
		
		while(!temp.eval().equals(temp))
			temp = temp.eval();
		
		return temp;
	}
	
	public abstract boolean equals(Expression e);

}