代码覆盖率：类覆盖，方法覆盖，行覆盖，指令覆盖……（简而言之，就是判断有没有被执行）
覆盖率 = 已经执行的代码 / 总代码
（1）创建maven项目，配置pom.xml如下
pom.xml
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>cn.demo</groupId>
<artifactId>answers</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging>
<name>answers</name>
<url>http://maven.apache.org</url>
<build>
<finalName>answers</finalName>
<plugins>
<plugin>
<inherited>true</inherited>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.1</version>
<configuration>
<source>${compiler.source}</source>
<target>${compiler.target}</target>
<encoding>${project.build.sourceEncoding}</encoding>
</configuration>
</plugin>
<!--检测代码覆盖率的插件-->
<plugin>
<groupId>org.jacoco</groupId>
<artifactId>jacoco-maven-plugin</artifactId>
<version>0.7.8</version>
<executions>
<execution>
<goals>
<goal>prepare-agent</goal>
</goals>
</execution>
<execution>
<id>report</id>
<phase>prepare-packag