访问者模式

src/main/java/top/fjy8018/designpattern/pattern/behavior/visitor/CodingCourse.java

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+package top.fjy8018.designpattern.pattern.behavior.visitor;
+
+import lombok.Data;
+import lombok.EqualsAndHashCode;
+
+/**
+ * 实战课，包含价格
+ *
+ * @author F嘉阳
+ * @date 2020/7/22 10:20
+ */
+@Data
+@EqualsAndHashCode(callSuper = true)
+public class CodingCourse extends Course {
+    private int price;
+
+    @Override
+    public void accept(IVisitor visitor) {
+        visitor.visit(this);
+    }
+}

src/main/java/top/fjy8018/designpattern/pattern/behavior/visitor/Course.java

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+package top.fjy8018.designpattern.pattern.behavior.visitor;
+
+import lombok.Data;
+
+/**
+ * @author F嘉阳
+ * @date 2020/7/22 10:20
+ */
+@Data
+public abstract class Course {
+    private String name;
+
+    public abstract void accept(IVisitor visitor);
+
+}

src/main/java/top/fjy8018/designpattern/pattern/behavior/visitor/FreeCourse.java

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+package top.fjy8018.designpattern.pattern.behavior.visitor;
+
+/**
+ * 免费课
+ *
+ * @author F嘉阳
+ * @date 2020/7/22 10:20
+ */
+public class FreeCourse extends Course {
+
+    /**
+     * 接受策略
+     *
+     * @param visitor
+     */
+    @Override
+    public void accept(IVisitor visitor) {
+        visitor.visit(this);
+    }
+}

src/main/java/top/fjy8018/designpattern/pattern/behavior/visitor/IVisitor.java

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+package top.fjy8018.designpattern.pattern.behavior.visitor;
+
+/**
+ * 封装操作数据结构的方法
+ *
+ * @author F嘉阳
+ * @date 2020/7/22 10:20
+ */
+public interface IVisitor {
+
+    void visit(FreeCourse freeCourse);
+
+    void visit(CodingCourse codingCourse);
+}

src/main/java/top/fjy8018/designpattern/pattern/behavior/visitor/Visitor.java

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+package top.fjy8018.designpattern.pattern.behavior.visitor;
+
+/**
+ * 访问者
+ * 核心：对不同类型产生不同的操作行为
+ * <p>
+ * jdk源码 {@link java.nio.file.FileVisitor} 实现对文件的访问
+ * spring源码 {@link org.springframework.beans.factory.config.BeanDefinitionVisitor} 遍历Bean具体属性并填充
+ *
+ * @author F嘉阳
+ * @date 2020/7/22 10:20
+ */
+public class Visitor implements IVisitor {
+
+    /**
+     * 访问免费课程，打印所有免费课程名称
+     *
+     * @param freeCourse
+     */
+    @Override
+    public void visit(FreeCourse freeCourse) {
+        System.out.println("免费课程:" + freeCourse.getName());
+    }
+
+    /**
+     * 访问实战课程，打印所有实战课程名称及价格
+     *
+     * @param codingCourse
+     */
+    @Override
+    public void visit(CodingCourse codingCourse) {
+        System.out.println("实战课程:" + codingCourse.getName() + " 价格:" + codingCourse.getPrice() + "元");
+    }
+
+}

src/test/java/top/fjy8018/designpattern/pattern/behavior/visitor/VisitorTest.java

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+package top.fjy8018.designpattern.pattern.behavior.visitor;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * @author F嘉阳
+ * @date 2020/7/22 16:19
+ */
+class VisitorTest {
+
+    @Test
+    void visit() {
+        List<Course> courseList = new ArrayList<>();
+
+        FreeCourse freeCourse = new FreeCourse();
+        freeCourse.setName("SpringMVC数据绑定");
+
+        CodingCourse codingCourse = new CodingCourse();
+        codingCourse.setName("Java设计模式精讲");
+        codingCourse.setPrice(299);
+        // 数组组装
+        courseList.add(freeCourse);
+        courseList.add(codingCourse);
+
+        for (Course course : courseList) {
+            course.accept(new Visitor());
+        }
+    }
+}