降雨繪圖（JAVA實作）

新開了一門外教課程，Object-oriented Programming(JAVA), 記錄一些學習經驗，以及部分和c++的區別感悟，本文為降雨繪圖作業demo, 大概要求是從一個.text檔案中找到用戶從console中輸入的城市，并將該城市的12個月的降雨量資料繪制，要求是不可以使用array等容器提前存盤資料，必須輸在用戶輸入后，在.text檔案中找到目標城市并繪圖，text檔案格式如下：
…
Beijing 20.8 52.4 67.3 22.3 55.0 76.3 20.8 52.4 67.3 22.3 55.0 76.3
…

• 從main開始編程，分析需求，模塊化每個部分，然后填充、調整、debug等等，
• 代碼的可讀性很重要（與c++記憶體管理課程中老師開頭講的一樣）
• throws FileNotFoundException / try catch機制很好用，幫助分析報錯的問題，
• Scanner掃進來的資料，需要用.next()/.nextInt()轉換資料型別，再進行操作，并且.next()每呼叫一次游標都往下個空格orTAB移動，
• java中.equals()
• DrawingPanel左上角是坐標軸原點
  自己的總結與思考，目前水平有限，若有建議歡迎指教！ 代碼如下：

package assignment;
import java.awt.*;
import java.util.*;
import java.io.*;

public class RainfallPlotter {

	private static final int MONTH_WIDTH = 70;
	private static final int NAME_WIDTH = 100;
	private static final int HEIGHT = 550;
	private static final int LINE_OFFSET = 25;
	private static final int WIDTH = 12 * MONTH_WIDTH;	
	private static final Color[] COLORS = { Color.RED, Color.BLUE, Color.GREEN };
	// global para of color index
	public static int I = -1;
	
	private static final String STOP = "stop";

	private static final String[] MONTHS_NAME = { "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec" };
	// relative path
	private static final String DATA_FILE = "./rainfall.txt";
	
	// object panel is used in all process-life, and never changed.
	private static final DrawingPanel panel = new DrawingPanel(WIDTH, HEIGHT);
	// object g is used in three method of my solution.
	private static final Graphics g = panel.getGraphics();
	
	/**
	 * The main program
	 * Plus. If the user input the four city it will be wrong. Maybe use the para I
	 * as the while loop stop condition( || )can solve this question.
	 */
	public static void main(String[] args) throws FileNotFoundException {
		
		menuOpen();
		
		// draw the panel.(No data)
		drawingPanel();      	
		
		// Scanner for console input of user
		Scanner consol_input = new Scanner(System.in); 
		
		do {
			System.out.print("City? ");
			
		} while( readDbFile(consol_input) );
		
		consol_input.close();
		
		menuClose();
		
	}

    
	private static void menuOpen()
	{
		System.out.println("Welcome to the Rainfall Plotter program!");
		System.out.println("You can plot the rainfall for up to 3 cities");
		System.out.println("You can stop plotting by entering 'stop' as the name of the city");
	}
	
	
	private static void menuClose()
	{
		System.out.println("Thank you for using the Rainfall Plotter program!");
	}
	
	
	// 
	private static boolean readDbFile(Scanner consol_input) throws FileNotFoundException
	{
		
		String answer = consol_input.nextLine().trim();
		
		// Scanner for user input
		if (answer.equals(STOP)) { return false; }    // 比 == 好用
		
		// Scanner for load file
		Scanner input_file = new Scanner(new File(DATA_FILE)); 
		
		
		while ( input_file.hasNextLine() ) {
			
			String line = input_file.nextLine();
			
			// Scanner for every row
			Scanner input_line = new Scanner(line);
			
			//注意這里不可以直接用input_line與string比較
			String city = input_line.next(); //每next一次都往下移
			
			// find city
			if (city.equals(answer))    // java 風格 相等             
			{
				// draw point on the panel 
				drawingPoint(input_line, answer);
				// scanner close. Draw over
				input_line.close();
				return true;
			}
			input_line.close();
		}
		
		input_file.close();
		System.out.println("City not found.");
		return true;
	}
	
	// 
	private static void drawingPoint(Scanner city, String answer)
	{
		// draw city name on the panel(avoid overlap too), and set the color.
		// I is index of color.
		++I;
		g.setColor(COLORS[I]);
		g.drawString(answer, NAME_WIDTH * I, LINE_OFFSET-5);
		
		// i and j is index of month
		int i = 0;
		double temp_point_next = 0;
		
		while (  city.hasNext() )
		{
			double temp_point = city.nextDouble();
			drawNum(temp_point, i);
			if (i != 0) { drawColorLine(temp_point, temp_point_next, i, i-1); }
			
			for (int j = i+1; j < i+2; j++)
			{
				temp_point_next = city.nextDouble();
				drawNum(temp_point_next, j);
				drawColorLine(temp_point, temp_point_next, i, j);
			}
			
			i = i + 2;
		}
		
	}
	
	private static void drawColorLine(double temp_point, double temp_point_next, int i, int j)
	{

		int point1 = doubleToIntPoint(temp_point);
		
		int point2 = doubleToIntPoint(temp_point_next);
		
		g.drawLine(MONTH_WIDTH * i - 5, HEIGHT - (LINE_OFFSET + point1), MONTH_WIDTH * j -5, HEIGHT - (LINE_OFFSET + point2)); 
		
	}
	

	private static void drawNum(double temp_point, int i)
	{
		String num = String.valueOf(temp_point);
		int point = doubleToIntPoint(temp_point);
		
		g.drawString(num, MONTH_WIDTH * i, HEIGHT - (LINE_OFFSET + point));
	}
	
	private static int doubleToIntPoint(double target)
	{
		target = (target * 10) / 3;
		int point = (int)target;
		return point;
	}
	
	private static void drawingPanel()
	{
		g.drawLine(0, LINE_OFFSET, WIDTH, LINE_OFFSET);
		g.drawLine(0, HEIGHT-LINE_OFFSET, WIDTH, HEIGHT-LINE_OFFSET);
		
		for (int i = 0; i < MONTHS_NAME.length; i++)
		{
			g.drawString(MONTHS_NAME[i], MONTH_WIDTH * i, HEIGHT);
			
			// "-5" to avoid "line" and "month text" overlap. For beauty
			g.drawLine(MONTH_WIDTH * i - 5, LINE_OFFSET, MONTH_WIDTH * i -5, HEIGHT); 
		}
	}
}