假设列表类型为int java

Question

I have a function that returns a list of values. I want to use the values in that list as parameters in another function.

private static List test(){
    List myList;
    mylist.add(1);
    return myList;
};

Now here's the catch. When I say

lst = test();
myFunction(lst.get(1));

lst.get(1) is type object. But myFunction requires an int. I've tried casting it into lots of things. When I say (int) lst.get(1); my compiler returns this error:

C:\Users\...\workspace\...\....txt
Exception in thread "main" java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Integer
    at ///.///.Encode(///.java:73)
    at ///.///.main(///.java:25)

When I just have it with no cast, I get this red underline and error:

The method ENCODEScrambleNum(int, int, int, int, String) in the type kriptik is not applicable for the arguments (Object, Object, Object, Object, String)

Method signature:

ENCODEScrambleNum(int, int, int, int, String)

Calling it:

ENCODEScrambleNum(key.get(0), key.get(1), key.get(2), key.get(3), str);

Is there a way that I can tell the computer before hand that the list type will be an int?

Thanks.

Answer 1

Oh yes, you can do that. Just by declaring the type of the list like this

private static List<Integer> test(){
    //List<Integer> myList; // list is not initialized yet(NPE is waiting for you)
    List<Integer> myList = new ArrayList<Integer>(); // List initialized
    mylist.add(1);
    return myList;
} // Why was a semi-colon here?

When you try to send list.get(1) as an int parameter, it'll be autoboxed. So you need not worry about that.

Answer 2

private static List test(){
    List myList;
    mylist.add(1);    //Here the value 1 is added at zeroth index.
    return myList;
}

Replace your code as

lst = test();
myFunction(lst.get(0));  //Retrieves the value at zeroth index.

instead of,

lst = test();
myFunction(lst.get(1)); //Retrieves the value at first index

because the List index starts from 0 and not from 1 .

Answer 3

I agree with RJ, if you specify the type of list as integer and use get() function, it will always return an integer. I tried below code, hope it helps :

private static List<Integer> test(){

List<Integer> myList = new ArrayList<Integer>(); 
for(int i=0; i<4; i++){ myList.add(i+10);} //included a for loop just to put something in the list
return myList;
}

private static String ENCODEScrambleNum(Integer get, Integer get0, Integer get1, Integer get2, String in_here) {
     return "I am " + in_here + " with list items-" + get + get0 + get1 + get2; //Dummy logic
}