How to draw simple graphics in java

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;//游戏区域10*10方块的起始横坐标
    private static final int sy = 50;//游戏区域10*10方块的起始纵坐标
    private static final int w = 40;//每个小方格的边长
    private static final int rw = 400;//游戏区域10*10方块的边长
    ...
}

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 {
            // 设置线条颜色为红色
            g.setColor(Color.RED);
            // 绘制外层矩形框
            g.drawRect(sx, sy, rw, rw);            
            /* 绘制水平10个，垂直10个方格。
             * 即水平方向9条线，垂直方向9条线，
             * 外围四周4条线已经画过了，不需要再画。
             * 同时内部64个方格填写数字。
             */
            for(int i = 1; i < 10; i ++) {
                // 绘制第i条竖直线
                g.drawLine(sx + (i * w), sy, sx + (i * w), sy + rw);
                // 绘制第i条水平线
                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;//小方格宽度
    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构造方法
     */
    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();
        }        
        // 获取专门用于在窗口界面上绘图的对象
        jg =  this.getGraphics();
        // 绘制游戏区域
        paintComponents(jg);         
    }
    public void paintComponents(Graphics g) {
        try {
            // 设置线条颜色为红色
            g.setColor(Color.RED);
            // 绘制外层矩形框
            g.drawRect(sx, sy, rw, rw);
            
            /* 绘制水平10个，垂直10个方格。
             * 即水平方向9条线，垂直方向9条线，
             * 外围四周4条线已经画过了，不需要再画。
             * 同时内部64个方格填写数字。
             */
            for(int i = 1; i < 10; i ++) {
                // 绘制第i条竖直线
                g.drawLine(sx + (i * w), sy, sx + (i * w), sy + rw);
                
                // 绘制第i条水平线
                g.drawLine(sx, sy + (i * w), sx + rw, sy + (i * w));
                
                // 填写第i行从第1个方格到第8个方格里面的数字（方格序号从0开始）
                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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