To draw basic graphics in Java, you can use the Graphics class in the Java class library, which is located in the java.awt package. In our own java program file, to use the Graphics class, we need to use the import java.awt.Graphics statement to import the Graphics class.

The Graphics class provides basic geometric drawing methods, mainly including: drawing line segments, drawing rectangles, drawing circles, drawing colored graphics, drawing ellipses, drawing arcs, drawing polygons, etc. This project only uses the function of drawing straight lines. For other graphic drawings, please click to view the Java API.

The drawLine() method of Graphics class: drawLine(int x1,int y1,int x2,int y2)

The function of this method Yes: Draws a line between the points (x1,y1) and (x2,y2) using the current color in this graphics context's coordinate system.

There are several concepts that need to be understood here:

1) Graphics context: In layman’s terms, it is the drawing environment. Each window component (such as the main window, button, etc.) has its own graphics context object. We use this object to draw pictures on the component. This object is the Graphics object.

2) How to obtain the graphics context: On which component we want to draw, just call the getGraphics() method of that component to obtain the graphics context object of the component, and then use this object to draw.

3), Java coordinate system:

The coordinate origin of Java (0, 0) is located in the upper left corner of the screen. The coordinate measurement is in pixels, and the horizontal right is the positive direction of the X-axis. Direction, vertically downward is the positive direction of the Y-axis. The value of each coordinate point represents the position of a pixel on the screen. The values ??of all coordinate points are integers, as shown in the following figure:

4). Current color: refers to the current color of the graphics context. Each graphics context has its own current color. The color can be obtained through the getColor() method of the Graphics object, and the color can be set by the setColor() method.

The example is as follows:

Step 1: Add member variables to the DrawSee class to describe the characteristics of the game area.

For the DrawSee class, the main function of this class is to interact with the user, that is, display the game area, display numbers, respond to the user's mouse click, display the results of the user's mouse click, etc. We now consider the problem of drawing a game area with 10 rows and 10 columns. First add the following four member variables to the DrawSee class:

import java.awt.Color;
import java.awt.Container;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
public class DrawSee extends JFrame {
    private static final int sx = 50;//游戲區(qū)域10*10方塊的起始橫坐標(biāo)
    private static final int sy = 50;//游戲區(qū)域10*10方塊的起始縱坐標(biāo)
    private static final int w = 40;//每個(gè)小方格的邊長
    private static final int rw = 400;//游戲區(qū)域10*10方塊的邊長
    ...
}

Step 2: Add a method to draw the game area (that is, draw a red grid with 10 rows and 10 columns)

public void paintComponents(Graphics g) {
        try {
            // 設(shè)置線條顏色為紅色
            g.setColor(Color.RED);
            // 繪制外層矩形框
            g.drawRect(sx, sy, rw, rw);            
            /* 繪制水平10個(gè)，垂直10個(gè)方格。
             * 即水平方向9條線，垂直方向9條線，
             * 外圍四周4條線已經(jīng)畫過了，不需要再畫。
             * 同時(shí)內(nèi)部64個(gè)方格填寫數(shù)字。
             */
            for(int i = 1; i < 10; i ++) {
                // 繪制第i條豎直線
                g.drawLine(sx + (i * w), sy, sx + (i * w), sy + rw);
                // 繪制第i條水平線
                g.drawLine(sx, sy + (i * w), sx + rw, sy + (i * w));                
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

Summary:

import java.awt.Color;
import java.awt.Container;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
/**
 * 
 * 程序入口
 *
 */
public class TestDrawLine {   
    public static void main(String[] args) {   
        new DrawSee();
    }   
}   
class DrawSee extends JFrame {
    private static final int sx = 50;//小方格寬度
    private static final int sy = 50;//小方格高度
    private static final int w = 40;
    private static final int rw = 400;
    private Graphics jg;
    private Color rectColor = new Color(0xf5f5f5);
    /**
     * DrawSee構(gòu)造方法
     */
    public DrawSee() {
        Container p = getContentPane();
        setBounds(100, 100, 500, 500);
        setVisible(true);
        p.setBackground(rectColor);
        setLayout(null);   
        setResizable(false);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);        
        try {    
            Thread.sleep(500);
        } catch (Exception e) {
            e.printStackTrace();
        }        
        // 獲取專門用于在窗口界面上繪圖的對象
        jg =  this.getGraphics();
        // 繪制游戲區(qū)域
        paintComponents(jg);         
    }
    public void paintComponents(Graphics g) {
        try {
            // 設(shè)置線條顏色為紅色
            g.setColor(Color.RED);
            // 繪制外層矩形框
            g.drawRect(sx, sy, rw, rw);
            
            /* 繪制水平10個(gè)，垂直10個(gè)方格。
             * 即水平方向9條線，垂直方向9條線，
             * 外圍四周4條線已經(jīng)畫過了，不需要再畫。
             * 同時(shí)內(nèi)部64個(gè)方格填寫數(shù)字。
             */
            for(int i = 1; i < 10; i ++) {
                // 繪制第i條豎直線
                g.drawLine(sx + (i * w), sy, sx + (i * w), sy + rw);
                
                // 繪制第i條水平線
                g.drawLine(sx, sy + (i * w), sx + rw, sy + (i * w));
                
                // 填寫第i行從第1個(gè)方格到第8個(gè)方格里面的數(shù)字（方格序號從0開始）
                for(int j = 0; j < 10; j ++) {
                    //drawString(g, j, i);                    
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

The result is as shown:

Recommended tutorial: Getting started with java development

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