泛型-原始类型警告的正确处理：

Question

When implementing a generic method, I used the following statement:

@SuppressWarning({"unchecked"})
private static <T extends Comparable<T>> T[] merge(T[] arrayA, T[] arrayB) {
  ...
  T[] result;

// This is the line that needs that gives warnings    
  result = (T[]) Array.newInstance(arrayA.getClass().getComponentType(), arrayA.length + arrayB.length);
  ...

Now, many programming sources state that it's good programming practice to avoid using @SuppressWarnings for unchecked raw types. In this case, however, I don't know how to address this warning in the code. Searching the net for best practice to instantiate generic types in Java doesn't give one clear approach. In fact, many of the solutions I found are less than ideal.

In this piece of code, what would be the best approach to remove the raw type warning without adding the @SuppressWarnings to the method? Is what I did the best approach?

Answer 1

In some cases you can't avoid @SuppressWarnings . Even standard JDK classes use @SuppressWarnings("unchecked") when dealing with generic arrays.

Example:

Arrays class:

@SuppressWarnings("unchecked")
public static <T> T[] copyOf(T[] original, int newLength) {
    return (T[]) copyOf(original, newLength, original.getClass());
}

Speaking of Arrays.copyOf , you can use that method combined with System.arraycopy instead of your current logic:

private static <T extends Comparable<T>> T[] merge(T[] arrayA, T[] arrayB) {
    T[] result = Arrays.copyOf (arrayA, arrayA.length+arrayB.length);
    System.arraycopy (arrayB, 0, result, arrayA.length, arrayB.length);
    return result;
}