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