public final class MyClass {
    private MyClass() {} // 私有构造
    
    // final静态工厂方法
    public static final MyClass createInstance() {
        return new MyClass();
    }
}

public class Parent {
    // 非final工厂方法，允许子类覆盖
    public static Parent create() {
        return new Parent();
    }
}

public class Child extends Parent {
    // 覆盖父类的工厂方法
    public static Parent create() {
        return new Child();
    }
}

public class CachedObject {
    private static final CachedObject INSTANCE = new CachedObject();
    
    private CachedObject() {}
    
    // final确保所有调用都使用相同的缓存实例
    public static final CachedObject getInstance() {
        return INSTANCE;
    }
}

public abstract class Shape {
    // 非final，允许不同形状有不同的创建逻辑
    public static Shape createShape(String type) {
        switch(type) {
            case "circle": return new Circle();
            case "square": return new Square();
            default: throw new IllegalArgumentException();
        }
    }
}