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java.lang.Objectcom.google.common.base.Preconditions
public final class Preconditions
Contains simple static methods to be called at the start of your own methods to verify correct arguments and state. This allows constructs such as
if (count <= 0) { throw new IllegalArgumentException("must be positive: " + count); }to be replaced with the more compact
checkArgument(count > 0, "must be positive: %s", count);Note that the sense of the expression is inverted; with
Preconditions
you declare what you expect to be true, just as you do with an
assert
or a JUnit assertTrue()
call.
Take care not to confuse precondition checking with other similar types
of checks! Precondition exceptions -- including those provided here, but also
IndexOutOfBoundsException
, NoSuchElementException
, UnsupportedOperationException
and others -- are used to signal that the
calling method has made an error. This tells the caller that it should
not have invoked the method when it did, with the arguments it did, or
perhaps ever. Postcondition or other invariant failures should not
throw these types of exceptions, perhaps using AssertionError
instead.
Note: The methods of the Preconditions
class are highly
unusual in one way: they are supposed to throw exceptions, and promise
in their specifications to do so even when given perfectly valid input. That
is, null
is a valid parameter to the method checkNotNull(Object)
-- and technically this parameter could be even marked
as Nullable
! -- yet the method will still throw an exception anyway,
because that's what its contract says to do.
Method Summary | ||
---|---|---|
static void |
checkArgument(boolean expression)
Ensures the truth of an expression involving one or more parameters to the calling method. |
|
static void |
checkArgument(boolean expression,
Object errorMessage)
Ensures the truth of an expression involving one or more parameters to the calling method. |
|
static void |
checkArgument(boolean expression,
String errorMessageFormat,
Object... errorMessageArgs)
Ensures the truth of an expression involving one or more parameters to the calling method. |
|
static
|
checkContentsNotNull(T iterable)
Ensures that an Iterable object passed as a parameter to the
calling method is not null and contains no null elements. |
|
static
|
checkContentsNotNull(T iterable,
Object errorMessage)
Ensures that an Iterable object passed as a parameter to the
calling method is not null and contains no null elements. |
|
static
|
checkContentsNotNull(T iterable,
String errorMessageFormat,
Object... errorMessageArgs)
Ensures that an Iterable object passed as a parameter to the
calling method is not null and contains no null elements. |
|
static
|
checkNotNull(T reference)
Ensures that an object reference passed as a parameter to the calling method is not null, throwing a NullPointerException if it is. |
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static
|
checkNotNull(T reference,
Object errorMessage)
Ensures that an object reference passed as a parameter to the calling method is not null, throwing a NullPointerException if it is. |
|
static
|
checkNotNull(T reference,
String errorMessageFormat,
Object... errorMessageArgs)
Ensures that an object reference passed as a parameter to the calling method is not null, throwing a NullPointerException if it is. |
|
static void |
checkState(boolean expression)
Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method. |
|
static void |
checkState(boolean expression,
Object errorMessage)
Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method. |
|
static void |
checkState(boolean expression,
String errorMessageFormat,
Object... errorMessageArgs)
Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method. |
Methods inherited from class java.lang.Object |
---|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Method Detail |
---|
public static void checkArgument(boolean expression)
expression
- a boolean expression
IllegalArgumentException
- if expression
is falsepublic static void checkArgument(boolean expression, Object errorMessage)
expression
- a boolean expressionerrorMessage
- the exception message to use if the check fails; will
be converted to a string using String.valueOf(Object)
only if
needed
IllegalArgumentException
- if expression
is falsepublic static void checkArgument(boolean expression, String errorMessageFormat, Object... errorMessageArgs)
expression
- a boolean expressionerrorMessageFormat
- the format string
for
the desired error messageerrorMessageArgs
- the arguments referenced by the format specifiers
in errorMessageFormat
.
IllegalArgumentException
- if expression
is false
NullPointerException
- if the check fails and either errorMessageFormat
or errorMessageArgs
is null (don't let this
happen)public static void checkState(boolean expression)
expression
- a boolean expression
IllegalStateException
- if expression
is falsepublic static void checkState(boolean expression, Object errorMessage)
expression
- a boolean expressionerrorMessage
- the exception message to use if the check fails; will
be converted to a string using String.valueOf(Object)
only if
needed
IllegalStateException
- if expression
is falsepublic static void checkState(boolean expression, String errorMessageFormat, Object... errorMessageArgs)
expression
- a boolean expressionerrorMessageFormat
- the format string
for
the desired error messageerrorMessageArgs
- the arguments referenced by the format specifiers
in errorMessageFormat
.
IllegalStateException
- if expression
is false
NullPointerException
- if the check fails and either errorMessageFormat
or errorMessageArgs
is null (don't let this
happen)public static <T> T checkNotNull(T reference)
NullPointerException
if it is.
reference
- an object reference
NullPointerException
- if reference
is nullpublic static <T> T checkNotNull(T reference, Object errorMessage)
NullPointerException
if it is.
reference
- an object referenceerrorMessage
- the exception message to use if the check fails; will
be converted to a string using String.valueOf(Object)
only if
needed
NullPointerException
- if reference
is nullpublic static <T> T checkNotNull(T reference, String errorMessageFormat, Object... errorMessageArgs)
NullPointerException
if it is.
reference
- an object referenceerrorMessageFormat
- the format string
for
the desired error messageerrorMessageArgs
- the arguments referenced by the format specifiers
in errorMessageFormat
.
NullPointerException
- if reference
is nullpublic static <T extends Iterable<?>> T checkContentsNotNull(T iterable)
Iterable
object passed as a parameter to the
calling method is not null and contains no null elements.
iterable
- any Iterable
object
iterable
reference just validated
NullPointerException
- if iterable
is null or contains at
least one null elementpublic static <T extends Iterable<?>> T checkContentsNotNull(T iterable, Object errorMessage)
Iterable
object passed as a parameter to the
calling method is not null and contains no null elements.
iterable
- any Iterable
objecterrorMessage
- the exception message to use if the check fails; will
be converted to a string using String.valueOf(Object)
only if
needed
iterable
reference just validated
NullPointerException
- if iterable
is null or contains at
least one null elementpublic static <T extends Iterable<?>> T checkContentsNotNull(T iterable, String errorMessageFormat, Object... errorMessageArgs)
Iterable
object passed as a parameter to the
calling method is not null and contains no null elements.
iterable
- any Iterable
objecterrorMessageFormat
- the format string
for
the desired error messageerrorMessageArgs
- the arguments referenced by the format specifiers
in errorMessageFormat
.
iterable
reference just validated
NullPointerException
- if iterable
is null or contains at
least one null element
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