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package org.checkerframework.checker.nullness;
import org.checkerframework.checker.nullness.qual.EnsuresNonNull;
import org.checkerframework.checker.nullness.qual.NonNull;
import org.checkerframework.checker.nullness.qual.Nullable;
/**
* Utility class for the Nullness Checker.
*
* To avoid the need to write the NullnessUtil class name, do:
*
*
import static org.checkerframework.checker.nullness.NullnessUtil.castNonNull;
*
* or
*
* import static org.checkerframework.checker.nullness.NullnessUtil.*;
*
* Runtime Dependency
*
*
Please note that using this class introduces a runtime dependency. This means that you need to
* distribute (or link to) the Checker Framework, along with your binaries.
*
*
To eliminate this dependency, you can simply copy this class into your own project.
*/
@SuppressWarnings({
"nullness", // Nullness utilities are trusted regarding nullness.
"cast" // Casts look redundant if Nullness Checker is not run.
})
public final class NullnessUtil {
private NullnessUtil() {
throw new AssertionError("shouldn't be instantiated");
}
/**
* A method that suppresses warnings from the Nullness Checker.
*
*
The method takes a possibly-null reference, unsafely casts it to have the @NonNull type
* qualifier, and returns it. The Nullness Checker considers both the return value, and also the
* argument, to be non-null after the method call. Therefore, the {@code castNonNull} method can
* be used either as a cast expression or as a statement. The Nullness Checker issues no
* warnings in any of the following code:
*
*
* // one way to use as a cast:
* {@literal @}NonNull String s = castNonNull(possiblyNull1);
*
* // another way to use as a cast:
* castNonNull(possiblyNull2).toString();
*
* // one way to use as a statement:
* castNonNull(possiblyNull3);
* possiblyNull3.toString();`
* }
*
* The {@code castNonNull} method is intended to be used in situations where the programmer
* definitively knows that a given reference is not null, but the type system is unable to make
* this deduction. It is not intended for defensive programming, in which a programmer cannot
* prove that the value is not null but wishes to have an earlier indication if it is. See the
* Checker Framework Manual for further discussion.
*
* The method throws {@link AssertionError} if Java assertions are enabled and the argument
* is {@code null}. If the exception is ever thrown, then that indicates that the programmer
* misused the method by using it in a circumstance where its argument can be null.
*
* @param ref a reference of @Nullable type
* @return the argument, casted to have the type qualifier @NonNull
*/
public static @EnsuresNonNull("#1") @NonNull T castNonNull(
@Nullable T ref) {
assert ref != null : "Misuse of castNonNull: called with a null argument";
return (@NonNull T) ref;
}
/**
* Like castNonNull, but whereas that method only checks and casts the reference itself, this
* traverses all levels of the argument array. The array is recursively checked to ensure that
* all elements at every array level are non-null.
*
* @see #castNonNull(Object)
*/
public static @EnsuresNonNull("#1")
@NonNull T @NonNull [] castNonNullDeep(T @Nullable [] arr) {
return (@NonNull T[]) castNonNullArray(arr);
}
/**
* Like castNonNull, but whereas that method only checks and casts the reference itself, this
* traverses all levels of the argument array. The array is recursively checked to ensure that
* all elements at every array level are non-null.
*
* @see #castNonNull(Object)
*/
public static @EnsuresNonNull("#1")
@NonNull T @NonNull [][] castNonNullDeep(T @Nullable [] @Nullable [] arr) {
return (@NonNull T[][]) castNonNullArray(arr);
}
/**
* Like castNonNull, but whereas that method only checks and casts the reference itself, this
* traverses all levels of the argument array. The array is recursively checked to ensure that
* all elements at every array level are non-null.
*
* @see #castNonNull(Object)
*/
public static @EnsuresNonNull("#1")
@NonNull T @NonNull [][][] castNonNullDeep(T @Nullable [] @Nullable [] @Nullable [] arr) {
return (@NonNull T[][][]) castNonNullArray(arr);
}
/**
* Like castNonNull, but whereas that method only checks and casts the reference itself, this
* traverses all levels of the argument array. The array is recursively checked to ensure that
* all elements at every array level are non-null.
*
* @see #castNonNull(Object)
*/
public static @EnsuresNonNull("#1")
@NonNull T @NonNull [][][][] castNonNullDeep(
T @Nullable [] @Nullable [] @Nullable [] @Nullable [] arr) {
return (@NonNull T[][][][]) castNonNullArray(arr);
}
/**
* Like castNonNull, but whereas that method only checks and casts the reference itself, this
* traverses all levels of the argument array. The array is recursively checked to ensure that
* all elements at every array level are non-null.
*
* @see #castNonNull(Object)
*/
public static @EnsuresNonNull("#1")
@NonNull T @NonNull [][][][][] castNonNullDeep(
T @Nullable [] @Nullable [] @Nullable [] @Nullable [] @Nullable [] arr) {
return (@NonNull T[][][][][]) castNonNullArray(arr);
}
private static @NonNull T @NonNull [] castNonNullArray(
T @Nullable [] arr) {
assert arr != null : "Misuse of castNonNullArray: called with a null array argument";
for (int i = 0; i < arr.length; ++i) {
assert arr[i] != null : "Misuse of castNonNull: called with a null array element";
checkIfArray(arr[i]);
}
return (@NonNull T[]) arr;
}
private static void checkIfArray(@NonNull Object ref) {
assert ref != null : "Misuse of checkIfArray: called with a null argument";
Class comp = ref.getClass().getComponentType();
if (comp != null) {
// comp is non-null for arrays, otherwise null.
if (comp.isPrimitive()) {
// Nothing to do for arrays of primitive type: primitives are
// never null.
} else {
castNonNullArray((Object[]) ref);
}
}
}
}