Java 15密封接口的4个实现约束实战指南

public sealed interface Shape permits Circle, Rectangle, Triangle {
    double area();
}
// 允许的实现类
final class Circle implements Shape {
    private final double radius;
    public Circle(double radius) { this.radius = radius; }
    public double area() { return Math.PI * radius * radius; }
}
non-sealed class Rectangle implements Shape {
    private final double width, height;
    public Rectangle(double w, double h) { width = w; height = h; }
    public double area() { return width * height; }
}

sealed class Result
data class Success(val data: String) : Result()
data class Error(val message: String) : Result()

public sealed class Shape permits Circle, Rectangle, Triangle {
    // 抽象形状类
}

class Vehicle:
    def __init__(self, name):
        self.name = name
    def start(self):
        print(f"{self.name} 启动")
class Car(Vehicle):
    def start(self):
        super().start()
        print(f"{self.name} 加速行驶")

package main
func main() {
    var age int = "twenty" // 类型错误
}

final class Base {
    void execute() { }
}
class Derived extends Base { // 编译错误：无法继承 final 类
}

public sealed abstract class Shape permits Circle, Rectangle, Triangle {}
final class Circle extends Shape {}           // 终结
non-sealed class Rectangle extends Shape {}  // 开放
sealed class Triangle extends Shape permits Isosceles, Equilateral {} // 再次密封

type Counter struct{ value int }
func (c Counter) IncByVal() { c.value++ }        // 不影响原对象
func (c *Counter) IncByPtr() { c.value++ }       // 修改原对象
var c Counter
c.IncByVal() // 值不变
c.IncByPtr() // 值递增

abstract class DataProcessor {
    public final void process() {
        readData();      // 通用逻辑
        parseData();     // 子类可重写
        validate();      // 钩子方法
        save();          // 通用保存
    }
    protected abstract void parseData();
    protected void validate() {} // 默认空实现
}

public sealed interface Vehicle permits Car, Bike { }
public final class Car implements Vehicle { }
public final class Bike implements Vehicle { }

// 包com.example.parent中的类
package com.example.parent;
class Parent { } // 包私有类
// 包com.example.child中的子类
package com.example.child;
import com.example.parent.Parent;
class Child extends Parent { } // 编译错误：cannot inherit from package-private class

sealed class NetworkResult {
    data class Success(val data: String) : NetworkResult()
    data class Error(val message: String) : NetworkResult()
}

UPDATE accounts 
SET balance = 100, version = version + 1 
WHERE id = 1 AND version = 3;

import redis
r = redis.Redis()
def acquire_lock(key, expire_time):
    return r.set(key, "locked", nx=True, ex=expire_time)

// 示例：边缘节点模型版本校验逻辑
func validateModelVersion(nodeID, expectedHash string) bool {
    currentHash := getNodeModelHash(nodeID)
    if currentHash != expectedHash {
        log.Printf("Node %s requires model update", nodeID)
        triggerOTAUpdate(nodeID, expectedHash)
        return false
    }
    return true
}