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java.lang.Objectcom.google.common.base.Preconditions
public final class Preconditions
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.
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 errorMessageTemplate,
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 errorMessageTemplate,
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. |
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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. |
|
static
|
checkNotNull(T reference,
String errorMessageTemplate,
Object... errorMessageArgs)
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, 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 errorMessageTemplate,
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)
IllegalArgumentException
- if expression
is falsepublic static void checkArgument(boolean expression, String errorMessageTemplate, Object... errorMessageArgs)
expression
- a boolean expressionerrorMessageTemplate
- a template for the exception message should the
check fail. The message is formed by replacing each %s
placeholder in the template with an argument. These are matched by
position - the first %s
gets errorMessageArgs[0]
, etc.
Unmatched arguments will be appended to the formatted message in square
braces. Unmatched placeholders will be left as-is.errorMessageArgs
- the arguments to be substituted into the message
template. Arguments are converted to strings using
String.valueOf(Object)
.
IllegalArgumentException
- if expression
is false
NullPointerException
- if the check fails and either errorMessageTemplate
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)
IllegalStateException
- if expression
is falsepublic static void checkState(boolean expression, String errorMessageTemplate, Object... errorMessageArgs)
expression
- a boolean expressionerrorMessageTemplate
- a template for the exception message should the
check fail. The message is formed by replacing each %s
placeholder in the template with an argument. These are matched by
position - the first %s
gets errorMessageArgs[0]
, etc.
Unmatched arguments will be appended to the formatted message in square
braces. Unmatched placeholders will be left as-is.errorMessageArgs
- the arguments to be substituted into the message
template. Arguments are converted to strings using
String.valueOf(Object)
.
IllegalStateException
- if expression
is false
NullPointerException
- if the check fails and either errorMessageTemplate
or errorMessageArgs
is null (don't let
this happen)public static <T> T checkNotNull(T reference)
reference
- an object reference
NullPointerException
- if reference
is nullpublic static <T> T checkNotNull(T reference, Object errorMessage)
reference
- an object referenceerrorMessage
- the exception message to use if the check fails; will
be converted to a string using String.valueOf(Object)
NullPointerException
- if reference
is nullpublic static <T> T checkNotNull(T reference, String errorMessageTemplate, Object... errorMessageArgs)
reference
- an object referenceerrorMessageTemplate
- a template for the exception message should the
check fail. The message is formed by replacing each %s
placeholder in the template with an argument. These are matched by
position - the first %s
gets errorMessageArgs[0]
, etc.
Unmatched arguments will be appended to the formatted message in square
braces. Unmatched placeholders will be left as-is.errorMessageArgs
- the arguments to be substituted into the message
template. Arguments are converted to strings using
String.valueOf(Object)
.
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
- the iterable to check the contents of
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
- the iterable to check the contents oferrorMessage
- the exception message to use if the check fails; will
be converted to a string using String.valueOf(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, String errorMessageTemplate, Object... errorMessageArgs)
Iterable
object passed as a parameter to the
calling method is not null and contains no null elements.
iterable
- the iterable to check the contents oferrorMessageTemplate
- a template for the exception message should the
check fail. The message is formed by replacing each %s
placeholder in the template with an argument. These are matched by
position - the first %s
gets errorMessageArgs[0]
, etc.
Unmatched arguments will be appended to the formatted message in square
braces. Unmatched placeholders will be left as-is.errorMessageArgs
- the arguments to be substituted into the message
template. Arguments are converted to strings using
String.valueOf(Object)
.
iterable
reference just validated
NullPointerException
- if iterable
is null or contains at
least one null element
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