Java实现一个类容器

 

新建2个类

public class Test1 {
}

public class Test2 {
    public void render() {
        System.out.println("Test2");
    }
}

public class ClassContainer {

    private final HashMap<Class<?>, Object> classes = new HashMap<>();

    public ClassContainer() {
        List<Class<?>> scanClasses = new ArrayList<>(List.of(Test1.class));//被扫描到的类 上个文章介绍了如何遍历类路径所有类
        scanClasses.forEach(it -> {
            try {
                classes.put(it, it.getConstructor().newInstance());//创建对象 直接newInstance的方法被弃用 所以需要获取无参构造方法再创建对象
            } catch (InstantiationException | IllegalAccessException | NoSuchMethodException | InvocationTargetException e) {
                e.printStackTrace();
            }
        });
    }

    public <T> T create(Class<T> klass, Object instance) {
        classes.put(klass, instance);
        return (T) classes.get(klass);
    }

    public <T> T create(Class<T> klass) {
        if (classes.get(klass) == null) {//如果这类没对象的话就创建
            try {
                classes.put(klass, klass.getConstructor().newInstance());
            } catch (InstantiationException | IllegalAccessException | InvocationTargetException | NoSuchMethodException e) {
                e.printStackTrace();
            }
        }
        return (T) classes.get(klass);//返回对象
    }

    public HashMap<Class<?>, Object> getClasses() {
        return classes;
    }
}

测试一下

public class Main {

    private static final ClassContainer classContainer = new ClassContainer();

    public static void main(String[] args) {
        System.out.println(classContainer.create(Test2.class));//第一次创建
        System.out.println(classContainer.create(Test2.class));//第二次创建和第一次创建对象相同
        System.out.println(classContainer.create(Test2.class, new Test2()));//容器内的类被重新创建
        for (Map.Entry<Class<?>, Object> classObjectEntry : classContainer.getClasses().entrySet()) {
            System.out.println(classObjectEntry.getKey());//遍历容器内的类
        }
    }
}