为什么 parameter.getType().isInstance(HttpServletRequest.class) return 是假的，但是使用“==”是真的

Question

Parameter[] ps = method.getParameters();

Map<String,Integer> map = new HashMap<String,Integer>();

for(int ij = 0;ij<ps.length;ij++){

    Parameter p = ps[ij];

    RequestParam rp = p.getAnnotation(RequestParam.class);

    if(rp != null){

        //do something

    }else {
        System.out.println(p.getType());
        System.out.println(p.getType().isInstance(HttpServletRequest.class));
        System.out.println(p.getType() == HttpServletRequest.class);
    }
}

输出是：

interface javax.servlet.http.HttpServletRequest
false
true

为什么用"isInstance"是假，用“==”是真？因为"instance of"无法判断implements关系？

Answer 1

该类型不是 HttpServletRequest class 的实例，它是 java.lang.Class 的实例，其中包含有关 HttpServletRequest class 的信息.

Answer 2

isInstance 等于 instanceOf

This method is the dynamic equivalent of the Java language instanceof operator.

方法 return 错误，因为您正在将 class（return 由 p.getType() 编辑）与另一个 class HttpServletRequest.class 相反，此方法需要一个实例，例如：

Dog bobby = new BobbyDog(); // class BobbyDog extends Dog
System.out.println(Dog.class.isInstance(bobby)); // correct use (return true)
System.out.println(Dog.class.isInstance(BobbyDog.class)); // incorrect use (return false)

等于运算符return为真，因为两个class相等

p.getType() == HttpServletRequest.class // true
HttpServletRequest.class == HttpServletRequest.class // true

如果你想判断实现关系你必须使用方法

isAssignableFrom(Class<?> cls)

Determines if the class or interface represented by this Class object is either the same as, or is a superclass or superinterface of, the class or interface represented by the specified Class parameter. It returns true if so; otherwise it returns false. If this Class object represents a primitive type, this method returns true if the specified Class parameter is exactly this Class object; otherwise it returns false.

为什么 parameter.getType().isInstance(HttpServletRequest.class) return 是假的，但是使用“==”是真的

why parameter.getType().isInstance(HttpServletRequest.class) return is false,but use "==" is true

java

instanceof