【Java】 Void 类型

void 也算一个类型，而且是基本数据类型

和其它数据类型一样提供了对应的包装类Void

每个包装类都提供一个TYPE字节实例，返回对应的原型类实例

public static void main(String[] args) {
    Class<?>[] basicTypes = {
        void.class,
        boolean.class,
        char.class,
        byte.class,
        short.class,
        int.class,
        long.class,
        float.class,
        double.class
    };
    Class<?>[] wrapperTypes = {
        Void.class,
        Boolean.class,
        Character.class,
        Byte.class,
        Short.class,
        Integer.class,
        Long.class,
        Float.class,
        Double.class
    };
    Class<?>[] typeInWrapperTypes = {
        Void.TYPE,
        Boolean.TYPE,
        Character.TYPE,
        Byte.TYPE,
        Short.TYPE,
        Integer.TYPE,
        Long.TYPE,
        Float.TYPE,
        Double.TYPE
    };
 
    System.out.println(Arrays.toString(basicTypes));
    System.out.println(Arrays.toString(wrapperTypes));
    System.out.println(Arrays.toString(typeInWrapperTypes));
    System.out.println(Arrays.equals(basicTypes, typeInWrapperTypes));
}

基础类型void 作为方法返回类型时，不能写return，否则编译报错

但是Void类型，必须提供返回值，返回Null值

public void fun1() {
    // return null;
}
public Void fun2() {
   return null;
}

可以通过反射设置Void类型，返回一个真实Void类型实例

public static Void fun() {
    try {
        Class<Void> voidClass = Void.class;
        Constructor<Void> declaredConstructor = voidClass.getDeclaredConstructor();
        declaredConstructor.setAccessible(true);
        Void aVoid = declaredConstructor.newInstance();
        System.out.println(aVoid + " by reflect");
        System.out.println("aVoid == null -> " + (aVoid == null));
        return aVoid;
    } catch (Exception e) {
        e.printStackTrace();
    }
    return null;
}