不兼容的类型编译错误

Question

link for my code error

Incompatible type found java.util.vector required HighRights. Sorry I am new to Java and I just don't understand how to do this question

Notice: in this exercises we will NOT use Generics

In the following program, the code in the method CountHighs is missing. Write the code for this method, which takes as argument the vector m and returns the number of objects in the vector that are instances of HighRights

The method should also: - check that the elements extracted from the vector are indeed instances of the classes HighRights or LowRights . If an element is not an instance of such classes, then the method should return -1.

• handle the NullPointerException in case the vector is null. Use the following code when catching the occurring exception:

   System.out.println("Error"); System.exit(0); return 0; 

(Hint:

1. use m.size() to get the number of elements in the vector m
2. use the keyword instanceof to check if an object is an instance of a class)

For example,

• if the vector m contains only two HighRights objects and one LowRights objects then CountHighs(m) will return 2
• if the vector m contains only two HighRights objects and one String objects then CountHighs(m) will return -1
• if the vector m contains only five LowRights objects no HighRights objects then CountHighs(m) will return 0

Any help/tips will be appreciated. Thank you very much.

Answer 1

You should post full code (not as image) and the error stack trace, but I think I know the problem. You have a public static int CountHighs(Vector m) method, and inside it you check condition m instanceof HighRights/LowRights - it's never true, a Vector is a Vector, not HighRights. You need to check if objects stored in the vector are HighRights or LowRights. To do this, you should use a loop:

for(Object obj : m){ //it will iterate over the vector `m`, with each iteration `obj` will be the next element
    if(obj instanceof HighRights){
        ++countHighRights;
    }
    else if(obj instanceof LowRights){
        //do nothing - you should only count HighRights
    }
    else{ //obj is neither HighRight nor LowRight
        return -1;
    }
}