demo.java

nanjing university cs 的java课件。 对新手很有用。付课件中源码。

import java.io.*;

public class Demo{
	public double[] roots(double a, double b, double c) throws NoRootsException{
		double[] roots = new double[2];
		if(a < 0){
			throw new NoRootsException("a<0");
		}
		double delta = (b*b)-(4*a*c);
		if(delta < 0){
			throw new NoRootsException("delta<0");
		}
		//System.out.println("delta: " + delta);
		delta = Math.sqrt(delta);
		//System.out.println("sqrt(delta): " + delta);
		roots[0] = (-b + delta)/(2*a);
		roots[1] = (-b - delta)/(2*a);
		return roots;
	}

	public static void main(String[] args){
		Demo demo = new Demo();
		KeyBoardReader kbr = new KeyBoardReader();
		System.out.println("please input a:");
		double a = kbr.readDouble();
		System.out.println("please input b:");
		double b = kbr.readDouble();
		System.out.println("please input c:");
		double c = kbr.readDouble();
		try{
			double[] results = demo.roots(a,b,c);
			System.out.println("results:");
			System.out.println("results[0]:" + results[0]);
			System.out.println("results[1]:" + results[1]);
		}
		catch(NoRootsException e){
			System.out.println("Exception: " + e);
		}
		
	}
}

class NoRootsException extends Exception{
	NoRootsException(String msg){
		super(msg);
	}
}


class KeyBoardReader{
	
	private BufferedReader br;
	
	public KeyBoardReader(){
		br = new BufferedReader(new InputStreamReader(System.in));
	}
	
	public BufferedReader getReader(){
		return this.br;
	}
	
	public void setReader(BufferedReader br){
		this.br = br;
	}
	
	public double readDouble(){
		double value = 0.0;
		try{
			String s = br.readLine();
			System.out.println("s: " + s);
			value = Double.parseDouble(s);
		}
		catch(Exception e){
			System.out.println("Exception: " + e.getMessage());
		}
		return value;
	}
}