Package io.flutter.util

## Class Preconditions

- java.lang.Object
- - io.flutter.util.Preconditions

-     public final class Preconditions
      extends Object

  Static convenience methods that help a method or constructor check whether it was invoked correctly (that is, whether its preconditions were met).

- - ### Method Summary

    All Methods Static Methods Concrete Methods
    Modifier and Type | Method | Description
    --- | --- | ---
    `static <T> T` | `checkNotNull​(T reference)` | Ensures that an object reference passed as a parameter to the calling method is not null.
    `static void` | `checkState​(boolean expression)` | Ensures the truth of an expression involving the state of the calling instance.
    `static void` | `checkState​(boolean expression, Object errorMessage)` | Ensures the truth of an expression involving the state of the calling instance.

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Method Detail

    - #### checkNotNull

          public static <T> T checkNotNull​(T reference)

      Ensures that an object reference passed as a parameter to the calling method is not null.
      Parameters:
        `reference` - an object reference
      Returns:
        the non-null reference that was validated
      Throws:
        `NullPointerException` - if `reference` is null

    - #### checkState

          public static void checkState​(boolean expression)

      Ensures the truth of an expression involving the state of the calling instance.
      Parameters:
        `expression` - a boolean expression that must be checked to be true
      Throws:
        `IllegalStateException` - if `expression` is false

    - #### checkState

          public static void checkState​(boolean expression,
                                        @Nullable
                                        Object errorMessage)

      Ensures the truth of an expression involving the state of the calling instance.
      Parameters:
        `expression` - a boolean expression that must be checked to be true
        `errorMessage` - the exception message to use if the check fails; will be converted to a string using `String.valueOf(Object)`
      Throws:
        `IllegalStateException` - if `expression` is false