Guava Preconditions tool parameter pre-check, guavapreconditions

Guava Preconditions tool parameter pre-check, guavapreconditions

Preconditions is a tool class provided by guava for code verification. It provides many important static verification methods.

It is used to simplify code verification or preprocessing in our work or development. It verifies the rationality before the logic starts to avoid data errors caused by too deep parameter input.

In addition, we can accurately display the problem where the verification criteria are not met.

Guava overload many methods on Preconditions to form the Preconditions tool class. It takes 5 minutes to see it.

1. checkArgument

CheckArgument (boolean expression, @ Nullable String errorMessageTemplate, @ Nullable Object... errorMessageArgs): Check whether the expression is true. If the expression is not true, an error message is displayed. Placeholders are allowed in the error message. // Check whether the expression is correct and use the placeholder to output the error message Preconditions. checkArgument (3> 4, "% s is wrong", "3> 4 ");

2. checkState

CheckState (boolean expression): checks whether the expression is true. It is generally used to verify whether the return value is true. CheckState (boolean expression, @ Nullable Object errorMessage): When the expression is false, the specified error message is displayed. CheckState (boolean expression, @ Nullable String errorMessageTemplate, @ Nullable Object... errorMessageArgs): a validation expression allows placeholders to be used in error messages. // Check whether the expression is correct and use the placeholder to output the error message. Use the method as the expression Preconditions. checkState (testState (), "% s is wrong", "testState ()");

3. checkNotNull

CheckNotNull (T reference): checks whether the object is null. CheckNotNull (T reference, @ Nullable Object errorMessage): if the Object is empty, the specified error message is displayed. CheckNotNull (T reference, @ Nullable String errorMessageTemplate, @ Nullable Object... errorMessageArgs): placeholders can be used in error messages. // Check whether the object is null and use the placeholder to output the error message Preconditions. checkNotNull (testObject (), "% s is null", "testObject ()");

4. checkElementIndex

CheckElementIndex (int index, int size, @ Nullable String desc): Check whether the index value of an element is valid. If the index is greater than or equal to 0 and smaller than the size, the error description is displayed when the element is invalid. CheckElementIndex (int index, int size): the error description is "index ". // Check whether the element index is valid. Use checkPositionIndex to verify Preconditions. checkElementIndex (17, list. size ());

5. checkPositionIndex

CheckPositionIndex (int index, int size, @ Nullable String desc): Check whether the index value of an element is valid. If the index is greater than or equal to 0 and smaller than or equal to size, the error description is displayed when the element is invalid. CheckPositionIndex (int index, int size): the error description is "index ". // Check whether the element index is valid. The checkPositionIndex check does not generate an exception Preconditions. checkPositionIndex (17, list. size () at the critical value ());

6. checkPositionIndexes

CheckPositionIndexes (int start, int end, int size): Check whether the length of the list smaller than or equal to start is size. // Check whether the index interval Preconditions. checkPositionIndexes (3, 11, list. size () is valid ());