Class Preconditions
- java.lang.Object
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- com.google.common.base.Preconditions
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@GwtCompatible public final class Preconditions extends Object
Simple static methods to be called at the start of your own methods to verify correct arguments and state. This allows constructs such asif (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 anassert
or a JUnitassertTrue
call.Warning: only the
"%s"
specifier is recognized as a placeholder in these messages, not the full range ofString.format(String, Object[])
specifiers.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.See the Guava User Guide on using
Preconditions
.- Since:
- 2.0 (imported from Google Collections Library)
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Method Summary
All Methods Static Methods Concrete Methods Modifier and Type Method Description 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 int
checkElementIndex(int index, int size)
Ensures thatindex
specifies a valid element in an array, list or string of sizesize
.static int
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 int
checkPositionIndex(int index, int size)
Ensures thatindex
specifies a valid position in an array, list or string of sizesize
.static int
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.
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Method Detail
-
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
-
checkArgument
public static void checkArgument(boolean expression, @Nullable Object errorMessage)
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
-
checkArgument
public static void checkArgument(boolean expression, @Nullable String errorMessageTemplate, @Nullable 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
public static void checkState(boolean expression, @Nullable Object errorMessage)
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, @Nullable String errorMessageTemplate, @Nullable 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
public static <T> T checkNotNull(T reference, @Nullable Object errorMessage)
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
-
checkNotNull
public static <T> T checkNotNull(T reference, @Nullable String errorMessageTemplate, @Nullable 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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checkElementIndex
public static int 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- Returns:
- the value of
index
- Throws:
IndexOutOfBoundsException
- ifindex
is negative or is not less thansize
IllegalArgumentException
- ifsize
is negative
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checkElementIndex
public static int checkElementIndex(int index, int size, @Nullable String desc)
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- Returns:
- the value of
index
- Throws:
IndexOutOfBoundsException
- ifindex
is negative or is not less thansize
IllegalArgumentException
- ifsize
is negative
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checkPositionIndex
public static int 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- Returns:
- the value of
index
- Throws:
IndexOutOfBoundsException
- ifindex
is negative or is greater thansize
IllegalArgumentException
- ifsize
is negative
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checkPositionIndex
public static int checkPositionIndex(int index, int size, @Nullable String desc)
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- Returns:
- the value of
index
- 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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