symbol.java

symbman（大学作业）

public class Symbol extends Expression {
	private String name;
	
	public Symbol(String name) {
		this.name = new String(name);
	}
	
	public Object clone() {
		return new Symbol(name);
	}
	
	public String getName() {return name; }
	
	public Expression eval() {
		Expression e = Memory.read(this);
		return (e==null)?this:e;
	}
	
	public boolean equals(Expression ex) {
		if(!(ex instanceof Symbol)) return false;
		Symbol s = (Symbol)ex;
		return(this.name.equals(s.name));
	}
		
	public String toString() {
		return "(" + name + ")";
	}
	
	public Expression derive(Symbol s) {
		return this.equals(s)?new NumericValue(1.):new NumericValue(0.);
	}
	
	public Expression simplify() {
		return this.eval();
	}

}