迪米特原则

src/main/java/top/fjy8018/designpattern/principle/demeter/Boss.java

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+package top.fjy8018.designpattern.principle.demeter;
+
+import lombok.extern.slf4j.Slf4j;
+
+import java.util.List;
+
+/**
+ * 迪米特法则（Law of Demeter）又叫作最少知识原则（Least Knowledge Principle 简写LKP），
+ * 就是说一个对象应当对其他对象有尽可能少的了解
+ * 和朋友交流，不和陌生人说话
+ * 朋友指的是出现在类成员变量、方法参数、返回值的对象
+ *
+ * @author F嘉阳
+ * @date 2018-09-22 17:02
+ */
+@Slf4j
+public class Boss {
+
+    /**
+     * 此处朋友为{@link TeamLeader},{@link DCourse}不是类成员变量、方法参数、返回值的对象，所以不应该在类内引用
+     * 即当前类知道的应该尽可能少
+     *
+     * @param teamLeader
+     */
+    public void commandCheckNumber(TeamLeader teamLeader) {
+        List courses = teamLeader.checkNumberOfCourses();
+        log.info("课程的数量是：{}", courses.size());
+    }
+}

src/main/java/top/fjy8018/designpattern/principle/demeter/DCourse.java

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+package top.fjy8018.designpattern.principle.demeter;
+
+/**
+ * @author F嘉阳
+ * @date 2018-09-22 17:04
+ */
+public class DCourse {
+}

src/main/java/top/fjy8018/designpattern/principle/demeter/TeamLeader.java

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+package top.fjy8018.designpattern.principle.demeter;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * @author F嘉阳
+ * @date 2018-09-22 17:04
+ */
+public class TeamLeader {
+
+    /**
+     * {@link DCourse}作为方法返回值，属于“朋友”
+     *
+     * @return
+     */
+    public List<DCourse> checkNumberOfCourses() {
+        List<DCourse> courseList = new ArrayList<DCourse>();
+        for (int i = 0; i < 20; i++) {
+            courseList.add(new DCourse());
+        }
+        return courseList;
+    }
+}

src/test/java/top/fjy8018/designpattern/principle/demeter/BossTest.java

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+package top.fjy8018.designpattern.principle.demeter;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class BossTest {
+
+    @Test
+    void commandCheckNumber() {
+        Boss boss = new Boss();
+        boss.commandCheckNumber(new TeamLeader());
+    }
+}