支配树的理解和实战

「爱情、让人受尽委屈。」 2022-09-09 04:47 60阅读 0赞

# 一 支配树（Dominator Tree） #

支配树的概念来自图论。

![watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBAY2hlbmdxaXVtaW5n_size_20_color_FFFFFF_t_70_g_se_x_16][]

![watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBAY2hlbmdxaXVtaW5n_size_20_color_FFFFFF_t_70_g_se_x_16 1][]

从下层到上层分析，可以从对象的引用图推导出对应的支配树。

![watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBAY2hlbmdxaXVtaW5n_size_19_color_FFFFFF_t_70_g_se_x_16][]

在 MAT 中，单击工具栏上的对象支配树按钮，可以打开对象支配树视图。

# 二 实战 #

## 1 代码 ##

package chapter03;
    
    import java.util.ArrayList;
    import java.util.List;
    
    /**
    * 有一个学生浏览网页的记录程序，它记录每个学生访问过的网站地址。
    * 它由三个部分组成：Student、WebPage和StudentTrace三个类
    * <p>
    * -XX:+HeapDumpBeforeFullGC -XX:HeapDumpPath=D:\mat_log\student.hprof
    */
    public class StudentTrace {
        static List<WebPage> webpages = new ArrayList<>();
    
        public static void createWebPages() {
            for (int i = 0; i < 100; i++) {
                WebPage wp = new WebPage();
                wp.setUrl("http://www." + Integer.toString(i) + ".com");
                wp.setContent(Integer.toString(i));
                webpages.add(wp);
            }
        }
    
        public static void main(String[] args) {
            createWebPages(); // 创建了 100 个网页
            // 创建 3 个学生对象
            Student st3 = new Student(3, "Tom"); // 访问 34 个网页
            Student st5 = new Student(5, "Jerry"); // 访问 21 个网页
            Student st7 = new Student(7, "Lily"); // 访问 15 个网页
    
            for (int i = 0; i < webpages.size(); i++) {
                if (i % st3.getId() == 0)
                    st3.visit(webpages.get(i));
                if (i % st5.getId() == 0)
                    st5.visit(webpages.get(i));
                if (i % st7.getId() == 0)
                    st7.visit(webpages.get(i));
            }
            webpages.clear();
            System.gc();
        }
    }
    
    /**
    * @className: Student
    * @description: 学生类
    * 浅堆大小为24，计算方法：
    * id：4个字节
    * name：4个字节
    * history：4个字节
    * 对象头：8个字节
    * 8字节对齐：4个字节
    * @date: 2021/8/29
    */
    class Student {
        private int id;
        private String name;
        private List history = new ArrayList();
    
        public Student(int id, String name) {
            super();
            this.id = id;
            this.name = name;
        }
    
        public int getId() {
            return id;
        }
    
        public void setId(int id) {
            this.id = id;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public List getHistory() {
            return history;
        }
    
        public void setHistory(List history) {
            this.history = history;
        }
    
        public void visit(WebPage wp) {
            if (wp != null) {
                history.add(wp);
            }
        }
    }
    
    class WebPage {
        private String url;
        private String content;
    
        public String getUrl() {
            return url;
        }
    
        public void setUrl(String url) {
            this.url = url;
        }
    
        public String getContent() {
            return content;
        }
    
        public void setContent(String content) {
            this.content = content;
        }
    }

## 2 支配树位置 ##

![watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBAY2hlbmdxaXVtaW5n_size_15_color_FFFFFF_t_70_g_se_x_16][]

## 3 打开后的样子 ##

![watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBAY2hlbmdxaXVtaW5n_size_20_color_FFFFFF_t_70_g_se_x_16 2][]

## 4 正则过滤功能 ##

![watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBAY2hlbmdxaXVtaW5n_size_20_color_FFFFFF_t_70_g_se_x_16 3][]

## 5 支配树分析 ##

![watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBAY2hlbmdxaXVtaW5n_size_20_color_FFFFFF_t_70_g_se_x_16 4][]

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