不兼容的操作数类型

Question

I have created a class and its child. Now, I need to check if the child is the instance of parent but I get Incompatible operand types.

class Vehicle {

}

class Car extends Vehicle {

}

public class Test {

    public static void main(String[] args) {
        Vehicle v = new Vehicle();
        Car c = new Car();

        if (c instanceof v) {
        }

    }

}

Answer 1

The instanceof keyword needs to be used as

ReferenceTypeExpression instanceof ReferenceType

You are using it as

ReferenceTypeExpression instanceof ReferenceTypeExpression 

You should instead have

if (c instanceof Vehicle) {

The above explains the correct use of the instanceof operator, but take note of JB Nizet's comment .

Answer 2

Use isAssignableFrom() method in Class class.

if (c.getClass().isAssignableFrom(v.getClass())) {
    ...
}

Answer 3

instanceof需要将参考变量a与类b进行比较。