????????????

public class Test{
	public static void main(String[] args){
			
		if(args.length<3){
			System.out.println("Usage: java Test \"n1\"\"op\"\"n2\"");
			System.exit(-1);
		}
		
		try{
			double d1 = Double.parseDouble(args[0]);
			}catch (NumberFormatException n){
				System.out.println("error");
				}
		try{
			double d2 = Double.parseDouble(args[2]);
			}catch (NumberFormatException n){
				System.out.println("error");
				}
		double d = 0;
		if(args[1].equals("+")) d = d1+d2;
		else if(args[1].equals("-")) d = d1-d2;
		else if(args[1].equals("x")) d = d1*d2;
		else if(args[1].equals("/")) d = d1/d2;
		else{
			System.out.println("Error operator!");
			System.exit(-1);
		}
		System.out.println(d);
	}
}

 提示找不到d1,d2对象