Class Preconditions
boolean
expression which is expected to be true
(or in the case of
checkNotNull
, an object reference which is expected to be non-null). When false
(or
null
) is passed instead, the Preconditions
method throws an unchecked exception,
which helps the calling method communicate to its caller that that caller has made
a mistake. Example: <p> /** * Returns the positive square root of the given value. * * @throws IllegalArgumentException if the value is negative *
/ public static double sqrt(double value) { Preconditions.checkArgument(value >= 0.0, "negative value: %s", value); // calculate the square root } <p> void exampleBadCaller() { double d = sqrt(-1.0); }
In this example, checkArgument
throws an IllegalArgumentException
to indicate
that exampleBadCaller
made an error in its call to sqrt
.
Warning about performance
The goal of this class is to improve readability of code, but in some circumstances this may come at a significant performance cost. Remember that parameter values for message construction must all be computed eagerly, and autoboxing and varargs array creation may happen as well, even when the precondition check then succeeds (as it should almost always do in production). In some circumstances these wasted CPU cycles and allocations can add up to a real problem. Performance-sensitive precondition checks can always be converted to the customary form:
if (value < 0.0) {
throw new IllegalArgumentException("negative value: " + value);
}
Other types of preconditions
Not every type of precondition failure is supported by these methods. Continue to throw
standard JDK exceptions such as NoSuchElementException
or UnsupportedOperationException
in the situations they are intended for.
Non-preconditions
It is of course possible to use the methods of this class to check for invalid conditions which are not the caller's fault. Doing so is not recommended because it is misleading to future readers of the code and of stack traces. See Conditional failures explained in the Guava User Guide for more advice.
java.util.Objects.requireNonNull()
Projects which use com.google.common
should generally avoid the use of Objects.requireNonNull(Object)
. Instead, use whichever of checkNotNull(Object)
is appropriate to the situation.
(The same goes for the message-accepting overloads.)
Only %s
is supported
In Preconditions
error message template strings, only the "%s"
specifier is
supported, not the full range of Formatter
specifiers. However, note that if
the number of arguments does not match the number of occurrences of "%s"
in the format
string, Preconditions
will still behave as expected, and will still include all argument
values in the error message; the message will simply not be formatted exactly as intended.
More information
See the Guava User Guide on
using
Preconditions
.
Imported from com.google.guava:17.0 Preconditions
- Author:
- Kevin Bourrillion
-
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> 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
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.
-
Method Details
-
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
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, 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)
-
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
-
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
-
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
-
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
-