feat(class26-28): 添加抽象类和枚举相关代码

- 新增抽象类 A 和 Animal，以及它们的子类 B、Cat 和 Dog
- 添加抽象方法和具体方法的实现
- 新增枚举类 Direction 和常量类 Constant
- 编写测试类 AdstractDemo1 和 Test2，演示抽象类和枚举的使用

src/class26/Constant.java

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+package class26;
+
+public class Constant {
+    public static final int UP = 0;
+    public static final int DOWN = 1;
+    public static final int LEFT = 2;
+    public static final int RIGHT = 3;
+}

src/class26/Direction.java

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+package class26;
+
+public enum Direction {
+    UP, DOWN, LEFT, RIGHT;
+}

src/class26/Test2.java

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+package class26;
+
+public class Test2 {
+    public static void main(String[] args) {
+        //枚举应用场景，信息分类和标志
+        //way1
+        move(Constant.UP);//常量，缺点：1.枚举值不能修改 2.枚举值不能重复
+
+        //way2
+        move2(Direction.UP);
+
+
+    }
+    public static void move2(Direction direction){
+        switch (direction){
+            case Direction.UP:
+                System.out.println("向上");
+                break;
+            case Direction.DOWN:
+                System.out.println("向下");
+                break;
+            case Direction.LEFT:
+                System.out.println("向左");
+                break;
+            case Direction.RIGHT:
+                System.out.println("向右");
+                break;
+            default:
+                System.out.println("无效");
+        }
+
+    }
+    public static void move(int direction){
+        switch (direction){
+            case Constant.UP:
+                System.out.println("向上");
+                break;
+            case Constant.DOWN:
+                System.out.println("向下");
+                break;
+            case Constant.LEFT:
+                System.out.println("向左");
+                break;
+            case Constant.RIGHT:
+                System.out.println("向右");
+                break;
+            default:
+                System.out.println("无效");
+        }
+
+    }
+}

src/class27/A.java

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+package class27;
+
+import lombok.Getter;
+import lombok.Setter;
+
+public abstract class A {
+    @Getter
+    @Setter
+    private String name;
+    @Getter
+    @Setter
+    private int age;
+
+    public A() {
+        System.out.println("A无参构造器");
+    }
+
+    public abstract void show();
+    public void show2(){
+        System.out.println("show2");
+    };
+
+}

src/class27/AdstractDemo1.java

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+package class27;
+
+public class AdstractDemo1 {
+    public static void main(String[] args) {
+//        A a = new A();  // 抽象类不能实例化
+
+        B b = new B();
+        b.show();
+        b.show2();
+        b.setName("张三");
+        b.setAge(18);
+        System.out.println(b.getName());
+        System.out.println(b.getAge());
+
+
+
+
+    }
+
+}

src/class27/B.java

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+package class27;
+
+public class B extends A{
+
+
+    @Override
+    public void show() {
+
+    }
+}

src/class28/Animal.java

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+package class28;
+
+public abstract class Animal {
+
+    public abstract void cry();
+
+}

src/class28/Cat.java

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+package class28;
+
+public class Cat extends Animal{
+
+    @Override
+    public void cry() {
+        System.out.println("🐱是喵喵喵地叫~~~");
+    }
+}

src/class28/Dog.java

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+package class28;
+
+public class Dog extends  Animal{
+    public void cry()
+    {
+        System.out.println("🐕是汪汪汪地叫~~~");
+    }
+}

src/class28/Test.java

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+package class28;
+
+public class Test {
+    public static void main(String[] args) {
+        Animal a = new Cat();
+        a.cry();
+    }
+}