手把手教你用Java代码画二叉树

r囧r小猫 2022-12-27 12:59 246阅读 0赞

最近在研究二叉树，所以需要经常画二叉树来弥补我的匮乏的想象力，但是画一颗二叉树也不是那么容易的事，不仅画的慢，还画的丑，昨天晚上睡觉的时候还在思考，能不能用代码来画二叉树呢？我确信这种方案是可行的，本文就来分享我的成果，其实用代码画二叉树挺有趣的。

另外，由于代码不是一成不变的，我会时不时改一些bug、或者做一些优化，因此我将代码上传到gitee仓库上面了，读者可以自行下载。附地址：[https://gitee.com/bobo\_tea/datastructure/tree/master/src/main/datastructure/com/bobo/group/tree/draw][https_gitee.com_bobo_tea_datastructure_tree_master_src_main_datastructure_com_bobo_group_tree_draw]

先来看一下效果,如图1所示。

![图片][3cbdd606a95e6138c149f9020c51ed13.png]

图1

结点类DrawNode如下所示。

public static class DrawNode{
        protected int val;
       protected DrawNode left;
       protected DrawNode right;
       public DrawNode() {}
       public DrawNode(int val) {
           this.val = val;
       }
       public DrawNode(int val, DrawNode left, DrawNode right) {
           this.val = val;
           this.left = left;
           this.right = right;
       }
    }

如果你的结点类可能叫Node或者TreeNode，你可以继承DrawNode类，从而不用修改代码就能画出你想要的树来。

我用硬编码构建了一棵树，就是图1中的树，如下所示。

public DrawNode build(){
            DrawNode e = new DrawNode(73);
            DrawNode h = new DrawNode(51);
            DrawNode i = new DrawNode(93);
            DrawNode j = new DrawNode(37);
            DrawNode k = new DrawNode(120);
            DrawNode l = new DrawNode(9);
            DrawNode f = new DrawNode(99,i,k);
            DrawNode c = new DrawNode(88,e,f);
            DrawNode g = new DrawNode(35,l,j);
            DrawNode d = new DrawNode(47,g,h);
            DrawNode b = new DrawNode(58,d,null);
            DrawNode a = new DrawNode(62,b,c);
            return a;
        }

画二叉树的三个核心方法：

*  firstTraverseAndDraw：一边中序遍历，一边画图。而画图是调用了drawOval方法和drawLine方法。
 *  drawOval：画圆圈、画圆圈里面的值。
 *  drawLine：画两个圆圈之间的连线。

画二叉树的入口方法：

*  drawEntrance(DrawNode drawNode)

main方法调用入口方法，进行画图。

public static void main(String[] args) throws IOException {
            Drawing d = new Drawing();
            //先构建一颗二叉树
            DrawNode root = d.build();
            //调用入口方法画图
            d.drawEntrance(root);
        }

图片保存位置用常量PATH表示。

private static final String PATH = "F:/tree.png";

完整代码如下所示。

import javax.imageio.ImageIO;
    import java.awt.*;
    import java.awt.image.BufferedImage;
    import java.io.FileOutputStream;
    import java.io.IOException;
    
    public class Drawing {
        // 以下是常量
        private static final String PATH = "F:/tree.png";
        // 画板长度
        private static final int WIDTH = 800;
        // 画板宽度
        private static final int HEIGHT = 500;
        // 圆形半径
        private static final int OVAL_RADIUS = 15;
        // 字体大小
        private static final int FONT_SIZE = 15;
        // 根据字体位数，选择字体偏移量
        private static final int offset_1 = 12;
        private static final int offset_2 = 9;
        private static final int offset_3 = 4;
        //画连线时的偏移量
        private static final int LINE_OFFSET = 3;
        //字体格式
        private static final String FONT_STYLE = "宋体";
        //图片格式
        private static final String IMAGE_STYLE = "PNG";
        //写数字时用到的偏移量
        private static final int FONT_OFFSET = 1;
        //父圆形与子圆形之间的偏移量
        private static final int OVAL_OFFSET = 10;
        //root结点的y坐标
        private static final int ROOT_Y = 50;
        //图形缓存区
        private BufferedImage bi;
        //画图笔
        private Graphics2D g2;
    
        //以下是变量
        // 当前圆位置和值
        private int my_x;
        private int my_y;
        private int val;
    
        // 当前字体位置
        private int my_font_x;
        private int my_font_y;
    
    
        private void initSettings(){
            //得到图片缓冲区
            bi = new BufferedImage(WIDTH,HEIGHT,BufferedImage.TYPE_INT_RGB);
            //得到绘制环境(这张图片的笔)
            g2 = (Graphics2D) bi.getGraphics();
            g2.fillRect(0,0,WIDTH,HEIGHT);
            g2.setBackground(Color.WHITE);
            g2.setColor(Color.BLACK);
            g2.setFont(new Font(FONT_STYLE,Font.PLAIN,FONT_SIZE));
        }
        private void closeSettings() throws IOException {
            ImageIO.write(bi,IMAGE_STYLE,new FileOutputStream(PATH));
        }
    
        public static class DrawNode{
            protected int val;
            protected DrawNode left;
            protected DrawNode right;
            public DrawNode() {}
            public DrawNode(int val) {
                this.val = val;
            }
            public DrawNode(int val, DrawNode left, DrawNode right) {
                this.val = val;
                this.left = left;
                this.right = right;
            }
        }
    
        /**
         * 画一个圆，包括数字
         */
        private void drawOval(){
            g2.drawOval(my_x,my_y,OVAL_RADIUS*2,OVAL_RADIUS*2);
            my_font_y = my_y+OVAL_RADIUS+FONT_SIZE/2-FONT_OFFSET;
            switch (String.valueOf(val).length()){
                case 1: my_font_x = my_x+offset_1;break;
                case 2: my_font_x = my_x+offset_2;break;
                case 3: my_font_x = my_x+offset_3;break;
                default: System.out.println("值为"+String.valueOf(val).length()+"位数，不支持！");
            }
            g2.drawString(String.valueOf(val),my_font_x,my_font_y);
        }
    
        /**
         * 画连线
         * @param isLeft 父结点与子结点的关系
         * @param parent_x 父结点的x坐标
         * @param parent_y 父结点的y坐标
         */
        private void drawLine(boolean isLeft,int parent_x,int parent_y){
            int parent_point_x;
            int parent_point_y;
            int my_point_x;
            int my_point_y;
            if(isLeft){
                parent_point_x = parent_x+OVAL_RADIUS/2-LINE_OFFSET;
                parent_point_y = parent_y+(3*OVAL_RADIUS)/2+LINE_OFFSET;
                my_point_x = my_x+(3*OVAL_RADIUS)/2+LINE_OFFSET;
                my_point_y = my_y+OVAL_RADIUS/2-LINE_OFFSET;
            }else{
                parent_point_x = parent_x+(3*OVAL_RADIUS)/2+LINE_OFFSET;
                parent_point_y = parent_y+(3*OVAL_RADIUS)/2+LINE_OFFSET;
                my_point_x = my_x+OVAL_RADIUS/2-LINE_OFFSET;
                my_point_y = my_y+OVAL_RADIUS/2-LINE_OFFSET;
            }
            g2.drawLine(parent_point_x,parent_point_y,my_point_x,my_point_y);
        }
    
        /**
         * 一边中序遍历一边画图
         * @param node
         */
        private void firstTraverseAndDraw(DrawNode parentNode,DrawNode node,boolean isLeft,int parent_x,int parent_y){
            if(node == null){
                return;
            }
            //只画当前结点，而不画父结点。但是要根据父结点与当前结点的关系，确定当前结点的位置，并将连线画出来
            val = node.val;
            if(parentNode == null){
                my_x = WIDTH/2 - OVAL_RADIUS;
                my_y = ROOT_Y;
            }else{
                my_y = parent_y+2*OVAL_RADIUS+OVAL_OFFSET;
                if(isLeft){
                    my_x = parent_x-2*OVAL_RADIUS-OVAL_OFFSET;
                }else{
                    my_x = parent_x+2*OVAL_RADIUS+OVAL_OFFSET;
                }
                drawLine(isLeft,parent_x,parent_y);
            }
            drawOval();
    
            // 递归画出左子树和右子树
            parent_x = my_x;
            parent_y = my_y;
            firstTraverseAndDraw(node,node.left,true,parent_x,parent_y);
            firstTraverseAndDraw(node,node.right,false,parent_x,parent_y);
        }
    
        public DrawNode build(){
            DrawNode e = new DrawNode(73);
            DrawNode h = new DrawNode(51);
            DrawNode i = new DrawNode(93);
            DrawNode j = new DrawNode(37);
            DrawNode k = new DrawNode(120);
            DrawNode l = new DrawNode(9);
            DrawNode f = new DrawNode(99,i,k);
            DrawNode c = new DrawNode(88,e,f);
            DrawNode g = new DrawNode(35,l,j);
            DrawNode d = new DrawNode(47,g,h);
            DrawNode b = new DrawNode(58,d,null);
            DrawNode a = new DrawNode(62,b,c);
            return a;
        }
        public void drawEntrance(DrawNode drawNode) throws IOException {
            initSettings();
            firstTraverseAndDraw(null,drawNode,true,0,0);
            closeSettings();
        }
    
        public static void main(String[] args) throws IOException {
            Drawing d = new Drawing();
            //先构建一颗二叉树
            DrawNode root = d.build();
            //调用入口方法画图
            d.drawEntrance(root);
        }
    
    }

最后扫码关注一下笔者的微信公众号再走吧，感谢！

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3hsXzE4MDM_size_16_color_FFFFFF_t_70][]

[https_gitee.com_bobo_tea_datastructure_tree_master_src_main_datastructure_com_bobo_group_tree_draw]: https://gitee.com/bobo_tea/datastructure/tree/master/src/main/datastructure/com/bobo/group/tree/draw
[3cbdd606a95e6138c149f9020c51ed13.png]: /images/20221120/fcdc72a0038d4297b3f3b2e4be936553.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3hsXzE4MDM_size_16_color_FFFFFF_t_70]: /images/20221120/f1f40e45ee7f40f6ba8045f4b8283de9.png