public class Preconditions extends Object
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: /** * 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 } 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
.
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);
}
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.
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)
or Verify#verifyNotNull(Object) is appropriate to the situation.
(The same goes for the message-accepting overloads.)
%s
is supportedIn Preconditions
error message template strings, only the "%s"
specifier is
supported, not the full range of Formatter
specifiers.
See the Guava User Guide on
using Preconditions
.
Modifier and Type | Method and Description |
---|---|
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 String |
checkNotNullNorEmpty(String reference,
Object errorMessage)
Ensures that a string reference passed as a parameter to the calling method is not null.
|
static <T extends Collection<?>> |
checkNotNullNorEmpty(T reference,
Object errorMessage)
Ensures that a collection reference passed as a parameter to the calling method is not null.
|
static void |
checkState(boolean expression,
String errorMessageTemplate,
Object... errorMessageArgs)
Ensures the truth of an expression involving the state of the calling instance, but not.
|
public 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 falseNullPointerException
- if the check fails and either errorMessageTemplate
or
errorMessageArgs
is null (don't let this happen)public 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 falseNullPointerException
- 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 referenceNullPointerException
- 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 String checkNotNullNorEmpty(String reference, Object errorMessage)
reference
- a string referenceerrorMessage
- the exception message to use if the check fails; will be converted to a
string using String.valueOf(Object)
NullPointerException
- if reference
is nullIllegalArgumentException
- if reference
is emptypublic static <T extends Collection<?>> T checkNotNullNorEmpty(T reference, Object errorMessage)
reference
- a collection referenceerrorMessage
- the exception message to use if the check fails; will be converted to a
string using String.valueOf(Object)
NullPointerException
- if reference
is nullIllegalArgumentException
- if reference
is emptyCopyright © 2020 JBoss by Red Hat. All rights reserved.