java - 警告 : [unchecked] unchecked cast while using Generic Array

Question

我正在创建我自己的集合类。但一开始，我就受到警告。我在此链接中使用How to create a generic array? 。但我已经收到警告了。

这是我的警告消息:

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

这是我的初学者代码:

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;
    }

}

如果我使用

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

我现在收到此错误消息:

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

Answer 1

如果您阅读了所提供问题的答案，它会非常全面地解释为什么显示警告，并且还提供了有效的解决方法。

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 e.g, if you have that code in the above method:

建议的类型安全代码。

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