设计 Shape、Square、Circle3个类，计算周长和面积，编写 ShapeTest 类创建子类对象和输出其周长、面积。数据转换的事件处理

好的，下面是对应的代码实现：

// Shape类
public abstract class Shape {
    public abstract double getArea();
    public abstract double getPerimeter();
}

// Square类
public class Square extends Shape {
    private double side;
    
    public Square(double side) {
        this.side = side;
    }
    
    @Override
    public double getArea() {
        return side * side;
    }
    
    @Override
    public double getPerimeter() {
        return 4 * side;
    }
}

// Circle类
public class Circle extends Shape {
    private double radius;
    private final double PI = 3.14159265358979323846;
    
    public Circle(double radius) {
        this.radius = radius;
    }
    
    @Override
    public double getArea() {
        return PI * radius * radius;
    }
    
    @Override
    public double getPerimeter() {
        return 2 * PI * radius;
    }
}

// ShapeTest类
public class ShapeTest {
    public static void main(String[] args) {
        Shape square = new Square(5);
        Shape circle = new Circle(3);
        
        System.out.println("Square area: " + square.getArea());
        System.out.println("Square perimeter: " + square.getPerimeter());
        System.out.println("Circle area: " + circle.getArea());
        System.out.println("Circle perimeter: " + circle.getPerimeter());
    }
}

关于数据转换的事件处理，我们可以在父类 Shape 中添加一些方法，例如将 Shape 转换为字符串表示，或者将字符串表示转换为 Shape 对象。在这里，我们可以考虑使用 JSON 格式，例如将 Square 对象转换为以下 JSON 字符串表示：

{
    "type": "square",
    "side": 5
}

这样的话，我们就可以使用一些 JSON 库来实现 Shape 对象和 JSON 字符串之间的转换。具体实现可以参考以下代码：

import com.fasterxml.jackson.annotation.JsonSubTypes;
import com.fasterxml.jackson.annotation.JsonTypeInfo;
import com.fasterxml.jackson.databind.ObjectMapper;

// Shape类
@JsonTypeInfo(
        use = JsonTypeInfo.Id.NAME,
        include = JsonTypeInfo.As.PROPERTY,
        property = "type")
@JsonSubTypes({
        @JsonSubTypes.Type(value = Square.class, name = "square"),
        @JsonSubTypes.Type(value = Circle.class, name = "circle")
})
public abstract class Shape {
    public abstract double getArea();
    public abstract double getPerimeter();
    
    public String toJson() throws Exception {
        ObjectMapper mapper = new ObjectMapper();
        return mapper.writeValueAsString(this);
    }
    
    public static Shape fromJson(String json) throws Exception {
        ObjectMapper mapper = new ObjectMapper();
        return mapper.readValue(json, Shape.class);
    }
}

// Square类
public class Square extends Shape {
    private double side;
    
    public Square(double side) {
        this.side = side;
    }
    
    @Override
    public double getArea() {
        return side * side;
    }
    
    @Override
    public double getPerimeter() {
        return 4 * side;
    }
    
    public double getSide() {
        return side;
    }
    
    public void setSide(double side) {
        this.side = side;
    }
}

// Circle类
public class Circle extends Shape {
    private double radius;
    private final double PI = 3.14159265358979323846;
    
    public Circle(double radius) {
        this.radius = radius;
    }
    
    @Override
    public double getArea() {
        return PI * radius * radius;
    }
    
    @Override
    public double getPerimeter() {
        return 2 * PI * radius;
    }
    
    public double getRadius() {
        return radius;
    }
    
    public void setRadius(double radius) {
        this.radius = radius;
    }
}

// ShapeTest类
public class ShapeTest {
    public static void main(String[] args) throws Exception {
        Shape square = new Square(5);
        Shape circle = new Circle(3);
        
        String squareJson = square.toJson();
        String circleJson = circle.toJson();
        
        Shape square2 = Shape.fromJson(squareJson);
        Shape circle2 = Shape.fromJson(circleJson);
        
        System.out.println(square2.getArea());
        System.out.println(circle2.getPerimeter());
    }
}

这里我们使用了 Jackson 库来实现 Shape 对象和 JSON 字符串之间的转换，同时为了实现多态，我们使用了 Jackson 中的 @JsonTypeInfo 和 @JsonSubTypes 注解。这样就可以实现 Shape 对象的序列化和反序列化，以及多态的处理。