Class Preconditions
if (count invalid input: '<'= 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
invalid reference
Nullable
This class may be used with the Google Web Toolkit (GWT).
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Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionstatic 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 <T extends Iterable<?>>
TcheckContentsNotNull
(T iterable) Ensures that anIterable
object passed as a parameter to the calling method is not null and contains no null elements.static <T extends Iterable<?>>
TcheckContentsNotNull
(T iterable, Object errorMessage) Ensures that anIterable
object passed as a parameter to the calling method is not null and contains no null elements.static <T extends Iterable<?>>
TcheckContentsNotNull
(T iterable, String errorMessageTemplate, Object... errorMessageArgs) Ensures that anIterable
object passed as a parameter to the calling method is not null and contains no null elements.static void
checkElementIndex
(int index, int size) Ensures thatindex
specifies a valid element in an array, list or string of sizesize
.static void
checkElementIndex
(int index, int size, String desc) Ensures thatindex
specifies a valid element in an array, list or string of sizesize
.static <T> T
checkNotNull
(T reference) Ensures that an object reference passed as a parameter to the calling method is not null.static <T> T
checkNotNull
(T reference, Object errorMessage) Ensures that an object reference passed as a parameter to the calling method is not null.static <T> T
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
checkPositionIndex
(int index, int size) Ensures thatindex
specifies a valid position in an array, list or string of sizesize
.static void
checkPositionIndex
(int index, int size, String desc) Ensures thatindex
specifies a valid position in an array, list or string of sizesize
.static void
checkPositionIndexes
(int start, int end, int size) Ensures thatstart
andend
specify a valid positions in an array, list or string of sizesize
, and are in order.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.private static boolean
containsOrIsNull
(Iterable<?> iterable) (package private) static String
Substitutes each%s
intemplate
with an argument.
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Constructor Details
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Preconditions
private Preconditions()
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Method Details
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checkArgument
public static void checkArgument(boolean expression) Ensures the truth of an expression involving one or more parameters to the calling method.- Parameters:
expression
- a boolean expression- Throws:
IllegalArgumentException
- ifexpression
is false
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checkArgument
Ensures the truth of an expression involving one or more parameters to the calling method.- Parameters:
expression
- a boolean expressionerrorMessage
- the exception message to use if the check fails; will be converted to a string usingString.valueOf(Object)
- Throws:
IllegalArgumentException
- ifexpression
is false
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checkArgument
public static void checkArgument(boolean expression, String errorMessageTemplate, Object... errorMessageArgs) Ensures the truth of an expression involving one or more parameters to the calling method.- Parameters:
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
getserrorMessageArgs[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 usingString.valueOf(Object)
.- Throws:
IllegalArgumentException
- ifexpression
is falseNullPointerException
- if the check fails and eithererrorMessageTemplate
orerrorMessageArgs
is null (don't let this happen)
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checkState
public 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.- Parameters:
expression
- a boolean expression- Throws:
IllegalStateException
- ifexpression
is false
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checkState
Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method.- Parameters:
expression
- a boolean expressionerrorMessage
- the exception message to use if the check fails; will be converted to a string usingString.valueOf(Object)
- Throws:
IllegalStateException
- ifexpression
is false
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checkState
public 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.- Parameters:
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
getserrorMessageArgs[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 usingString.valueOf(Object)
.- Throws:
IllegalStateException
- ifexpression
is falseNullPointerException
- if the check fails and eithererrorMessageTemplate
orerrorMessageArgs
is null (don't let this happen)
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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
- ifreference
is null
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checkNotNull
Ensures that an object reference passed as a parameter to the calling method is not null.- Parameters:
reference
- an object referenceerrorMessage
- the exception message to use if the check fails; will be converted to a string usingString.valueOf(Object)
- Returns:
- the non-null reference that was validated
- Throws:
NullPointerException
- ifreference
is null
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checkNotNull
public static <T> T checkNotNull(T reference, String errorMessageTemplate, Object... errorMessageArgs) Ensures that an object reference passed as a parameter to the calling method is not null.- Parameters:
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
getserrorMessageArgs[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 usingString.valueOf(Object)
.- Returns:
- the non-null reference that was validated
- Throws:
NullPointerException
- ifreference
is null
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checkContentsNotNull
Ensures that anIterable
object passed as a parameter to the calling method is not null and contains no null elements.- Parameters:
iterable
- the iterable to check the contents of- Returns:
- the non-null
iterable
reference just validated - Throws:
NullPointerException
- ifiterable
is null or contains at least one null element
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checkContentsNotNull
Ensures that anIterable
object passed as a parameter to the calling method is not null and contains no null elements.- Parameters:
iterable
- the iterable to check the contents oferrorMessage
- the exception message to use if the check fails; will be converted to a string usingString.valueOf(Object)
- Returns:
- the non-null
iterable
reference just validated - Throws:
NullPointerException
- ifiterable
is null or contains at least one null element
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checkContentsNotNull
public static <T extends Iterable<?>> T checkContentsNotNull(T iterable, String errorMessageTemplate, Object... errorMessageArgs) Ensures that anIterable
object passed as a parameter to the calling method is not null and contains no null elements.- Parameters:
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
getserrorMessageArgs[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 usingString.valueOf(Object)
.- Returns:
- the non-null
iterable
reference just validated - Throws:
NullPointerException
- ifiterable
is null or contains at least one null element
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containsOrIsNull
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checkElementIndex
public static void checkElementIndex(int index, int size) Ensures thatindex
specifies a valid element in an array, list or string of sizesize
. An element index may range from zero, inclusive, tosize
, exclusive.- Parameters:
index
- a user-supplied index identifying an element of an array, list or stringsize
- the size of that array, list or string- Throws:
IndexOutOfBoundsException
- ifindex
is negative or is not less thansize
IllegalArgumentException
- ifsize
is negative
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checkElementIndex
Ensures thatindex
specifies a valid element in an array, list or string of sizesize
. An element index may range from zero, inclusive, tosize
, exclusive.- Parameters:
index
- a user-supplied index identifying an element of an array, list or stringsize
- the size of that array, list or stringdesc
- the text to use to describe this index in an error message- Throws:
IndexOutOfBoundsException
- ifindex
is negative or is not less thansize
IllegalArgumentException
- ifsize
is negative
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checkPositionIndex
public static void checkPositionIndex(int index, int size) Ensures thatindex
specifies a valid position in an array, list or string of sizesize
. A position index may range from zero tosize
, inclusive.- Parameters:
index
- a user-supplied index identifying a position in an array, list or stringsize
- the size of that array, list or string- Throws:
IndexOutOfBoundsException
- ifindex
is negative or is greater thansize
IllegalArgumentException
- ifsize
is negative
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checkPositionIndex
Ensures thatindex
specifies a valid position in an array, list or string of sizesize
. A position index may range from zero tosize
, inclusive.- Parameters:
index
- a user-supplied index identifying a position in an array, list or stringsize
- the size of that array, list or stringdesc
- the text to use to describe this index in an error message- Throws:
IndexOutOfBoundsException
- ifindex
is negative or is greater thansize
IllegalArgumentException
- ifsize
is negative
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checkPositionIndexes
public static void checkPositionIndexes(int start, int end, int size) Ensures thatstart
andend
specify a valid positions in an array, list or string of sizesize
, and are in order. A position index may range from zero tosize
, inclusive.- Parameters:
start
- a user-supplied index identifying a starting position in an array, list or stringend
- a user-supplied index identifying a ending position in an array, list or stringsize
- the size of that array, list or string- Throws:
IndexOutOfBoundsException
- if either index is negative or is greater thansize
, or ifend
is less thanstart
IllegalArgumentException
- ifsize
is negative
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format
Substitutes each%s
intemplate
with an argument. These are matched by position - the first%s
getsargs[0]
, etc. If there are more arguments than placeholders, the unmatched arguments will be appended to the end of the formatted message in square braces.- Parameters:
template
- a non-null string containing 0 or more%s
placeholders.args
- the arguments to be substituted into the message template. Arguments are converted to strings usingString.valueOf(Object)
. Arguments can be null.
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