警告：[使用通用数组时未选中]未选中的强制类型转换

Question

I am creating my own set class . But At the beginning , I take a warning. I use in this link How to create a generic array? . But I have already take warning.

This is my warning message:

MySet.java:11: warning: [unchecked] unchecked cast
        data = (T[]) new Object[10];
                     ^
  required: T[]
  found:    Object[]
  where T is a type-variable:
    T extends Object declared in class MySet
1 warning

This is my beginner code:

Main.java

public class Main{

    public static void main(String[] args){

        MySet<Integer> a = new MySet<Integer>();

        System.out.printf("empty or not = %d\n",a.empty());

    }

}

MySetInterface.java

public interface MySetInterface<T> {
    public int empty();
}

MySet.java

public class MySet<T> implements MySetInterface<T>{

private T[] data;
private int used;
private int capacity;

public MySet(){

    used = 0;
    capacity = 1024;
    data = (T[]) new Object[10];
}

public int empty(){

    if(used == 0){
        return 1;
    }
    else{
        return 0;
    }

}

If I use

@SuppressWarnings("unchecked")
        data = (T[]) new Object[10];

I take this error message now:

MySet.java:12: error: <identifier> expected
        data = (T[]) new Object[10];
            ^
1 error

Answer 1

If you read the answer to the question that you provided it gives a very thorough explanation as to why the warning is shown and it also provided a valid workaround.

The above code have the same implications as explained above. If you notice, the compiler would be giving you an Unchecked Cast Warning there, as you are typecasting to an array of unknown component type. That means, the cast may fail at runtime. For eg, if you have that code in the above method:

Suggested typesafe code.

public <E> E[] getArray(Class<E> clazz, int size) {
    @SuppressWarnings("unchecked")
    E[] arr = (E[]) Array.newInstance(clazz, size);

    return arr;
}

Explanation is provided in the answer