设计模式composite计算器

package composite;
public class Expression implements Element{
	private Element e1,e2;
	private char op;
	
	public Expression(Element e1,Element e2,char op){
		this.e1=e1;
		this.e2=e2;
		this.op=op;
	}
	
	public double getValue(){
		switch(op){
		case '+' :return e1.getValue()+e2.getValue();
		case '-' :return e1.getValue()-e2.getValue();
		case '*' :return e1.getValue()*e2.getValue();
		case '/' :return e1.getValue()/e2.getValue();
		default: throw new RuntimeException("无效的运算符！");
		}
	}
	public static void main(String[] args) {
		Number n1 = new Number(1);
		Number n2 = new Number(2);
		Expression e1 = new Expression(n1, n2, '*');
		System.out.println(e1.getValue());
	}
}

package composite;public class Number implements Element{private double num;public Number(double num){this.num=num;}public double getValue(){return num;}}

package composite;interface Element { double getValue();}