合成复用原则

src/main/java/top/fjy8018/designpattern/principle/compositionaggregation/after/ADBConnection.java

@@ -0,0 +1,11 @@
+package top.fjy8018.designpattern.principle.compositionaggregation.after;
+
+/**
+ * 合成复用原则：要尽量使用组合，尽量不要使用继承
+ *
+ * @author F嘉阳
+ * @date 2018-09-23 15:50
+ */
+public abstract class ADBConnection {
+    public abstract String getConnection();
+}

src/main/java/top/fjy8018/designpattern/principle/compositionaggregation/after/AProductDao.java

@@ -0,0 +1,26 @@
+package top.fjy8018.designpattern.principle.compositionaggregation.after;
+
+import lombok.extern.slf4j.Slf4j;
+
+/**
+ * @author F嘉阳
+ * @date 2018-09-23 15:51
+ */
+@Slf4j
+public class AProductDao {
+
+    private final ADBConnection connection;
+
+    /**
+     * 通过构造器注入，解除继承关系，同时符合里氏替换原则和开闭原则
+     *
+     * @param connection
+     */
+    public AProductDao(ADBConnection connection) {
+        this.connection = connection;
+    }
+
+    public void addProduct() {
+        log.info("使用{}", connection.getConnection());
+    }
+}

src/main/java/top/fjy8018/designpattern/principle/compositionaggregation/after/MysqlConnection.java

@@ -0,0 +1,12 @@
+package top.fjy8018.designpattern.principle.compositionaggregation.after;
+
+/**
+ * @author F嘉阳
+ * @date 2018-09-23 15:56
+ */
+public class MysqlConnection extends ADBConnection {
+    @Override
+    public String getConnection() {
+        return "MySQL数据库连接";
+    }
+}

src/main/java/top/fjy8018/designpattern/principle/compositionaggregation/after/OracleConnection.java

@@ -0,0 +1,12 @@
+package top.fjy8018.designpattern.principle.compositionaggregation.after;
+
+/**
+ * @author F嘉阳
+ * @date 2018-09-23 15:57
+ */
+public class OracleConnection extends ADBConnection {
+    @Override
+    public String getConnection() {
+        return "Oracle数据库连接";
+    }
+}

src/main/java/top/fjy8018/designpattern/principle/compositionaggregation/before/DBConnection.java

@@ -0,0 +1,13 @@
+package top.fjy8018.designpattern.principle.compositionaggregation.before;
+
+/**
+ * 合成复用原则：要尽量使用组合，尽量不要使用继承
+ *
+ * @author F嘉阳
+ * @date 2018-09-23 15:50
+ */
+public class DBConnection {
+    public String getConnection() {
+        return "MySQL数据库连接";
+    }
+}

src/main/java/top/fjy8018/designpattern/principle/compositionaggregation/before/ProductDao.java

@@ -0,0 +1,17 @@
+package top.fjy8018.designpattern.principle.compositionaggregation.before;
+
+import lombok.extern.slf4j.Slf4j;
+
+/**
+ * 直接使用继承，属于聚合关系，业务变更困难
+ *
+ * @author F嘉阳
+ * @date 2018-09-23 15:51
+ */
+@Slf4j
+public class ProductDao extends DBConnection {
+
+    public void addProduct() {
+        log.info("使用{}", super.getConnection());
+    }
+}

src/main/java/top/fjy8018/designpattern/principle/liskovsubstitution/method/input/after/Child.java

@@ -6,7 +6,7 @@ import java.util.HashMap;
 import java.util.Map;
 
 /**
- * 李氏转换原则要求方法入参必须比父类范围更宽，返回值必须比父类更窄
+ * 里氏替换原则要求方法入参必须比父类范围更宽，返回值必须比父类更窄
  *
  * @author F嘉阳
  * @date 2018-09-23 11:30

src/test/java/top/fjy8018/designpattern/principle/compositionaggregation/before/ProductDaoTest.java

@@ -0,0 +1,26 @@
+package top.fjy8018.designpattern.principle.compositionaggregation.before;
+
+import org.junit.jupiter.api.Test;
+import top.fjy8018.designpattern.principle.compositionaggregation.after.AProductDao;
+import top.fjy8018.designpattern.principle.compositionaggregation.after.MysqlConnection;
+import top.fjy8018.designpattern.principle.compositionaggregation.after.OracleConnection;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class ProductDaoTest {
+
+    @Test
+    void before() {
+        ProductDao productDao = new ProductDao();
+        productDao.addProduct();
+    }
+
+    @Test
+    void after() {
+        // 变更交由业务层决定
+        AProductDao productDao1 = new AProductDao(new MysqlConnection());
+        productDao1.addProduct();
+        AProductDao productDao2 = new AProductDao(new OracleConnection());
+        productDao2.addProduct();
+    }
+}