Top Description Constructors Methods
com.google.common.base

public final Class Preconditions

extends Object
Class Inheritance
Annotations
@GwtCompatible
@ElementTypesAreNonnullByDefault
Static Imports
com.google.common.base.Strings.lenientFormat
Static convenience methods that help a method or constructor check whether it was invoked correctly (that is, whether its preconditions were met).

If the precondition is not met, the Preconditions method throws an unchecked exception of a specified type, which helps the method in which the exception was thrown communicate that its caller has made a mistake. This allows constructs such as 

public static double sqrt(double value) {
  if (value < 0) {
    throw new IllegalArgumentException("input is negative: " + value);
  }
  // calculate square root
}

to be replaced with the more compact 

public static double sqrt(double value) {
  checkArgument(value >= 0, "input is negative: %s", value);
  // calculate square root
}

so that a hypothetical bad caller of this method, such as: 

void exampleBadCaller() {
  double d = sqrt(-1.0);
}

would be flagged as having called sqrt() with an illegal argument.

Performance

Avoid passing message arguments that are expensive to compute; your code will always compute them, even though they usually won't be needed. If you have such arguments, use the conventional if/throw idiom instead.

Depending on your message arguments, memory may be allocated for boxing and varargs array creation. However, the methods of this class have a large number of overloads that prevent such allocations in many common cases.

The message string is not formatted unless the exception will be thrown, so the cost of the string formatting itself should not be a concern.

As with any performance concerns, you should consider profiling your code (in a production environment if possible) before spending a lot of effort on tweaking a particular element.

Other types of preconditions

Not every type of precondition failure is supported by these methods. Continue to throw standard JDK exceptions such as java.util.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. Notably, Verify offers assertions similar to those in this class for non-precondition checks.

java.util.Objects.requireNonNull()

Projects which use com.google.common should generally avoid the use of java.util.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.)

Only %s is supported

Preconditions uses Strings#lenientFormat to format error message template strings. This only supports the "%s" specifier, not the full range of java.util.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.

Author
Kevin Bourrillion
Since
2.0

Constructor Summary

AccessConstructor and Description
private
Preconditions()

Method Summary

Modifier and TypeMethod and Description
private static String
badElementIndex(int index, int size, String desc)

private static String
badPositionIndex(int index, int size, String desc)

private static String
badPositionIndexes(int start, int end, int size)

public static void
checkArgument(boolean
a boolean expression
expression)

Ensures the truth of an expression involving one or more parameters to the calling method.

public static void
checkArgument(boolean
a boolean expression
expression, Object
the exception message to use if the check fails; will be converted to a string using String#valueOf(Object)
errorMessage)

Ensures the truth of an expression involving one or more parameters to the calling method.

public static void
checkArgument(boolean
a boolean expression
expression, String
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.
errorMessageTemplate, @Nullable Object...
the arguments to be substituted into the message template. Arguments are converted to strings using String#valueOf(Object).
errorMessageArgs)

Ensures the truth of an expression involving one or more parameters to the calling method.

public static void
checkArgument(boolean expression, String errorMessageTemplate, char p1)

Ensures the truth of an expression involving one or more parameters to the calling method.

public static void
checkArgument(boolean expression, String errorMessageTemplate, int p1)

Ensures the truth of an expression involving one or more parameters to the calling method.

public static void
checkArgument(boolean expression, String errorMessageTemplate, long p1)

Ensures the truth of an expression involving one or more parameters to the calling method.

public static void
checkArgument(boolean expression, String errorMessageTemplate, Object p1)

Ensures the truth of an expression involving one or more parameters to the calling method.

public static void
checkArgument(boolean expression, String errorMessageTemplate, char p1, char p2)

Ensures the truth of an expression involving one or more parameters to the calling method.

public static void
checkArgument(boolean expression, String errorMessageTemplate, char p1, int p2)

Ensures the truth of an expression involving one or more parameters to the calling method.

public static void
checkArgument(boolean expression, String errorMessageTemplate, char p1, long p2)

Ensures the truth of an expression involving one or more parameters to the calling method.

public static void
checkArgument(boolean expression, String errorMessageTemplate, char p1, Object p2)

Ensures the truth of an expression involving one or more parameters to the calling method.

public static void
checkArgument(boolean expression, String errorMessageTemplate, int p1, char p2)

Ensures the truth of an expression involving one or more parameters to the calling method.

public static void
checkArgument(boolean expression, String errorMessageTemplate, int p1, int p2)

Ensures the truth of an expression involving one or more parameters to the calling method.

public static void
checkArgument(boolean expression, String errorMessageTemplate, int p1, long p2)

Ensures the truth of an expression involving one or more parameters to the calling method.

public static void
checkArgument(boolean expression, String errorMessageTemplate, int p1, Object p2)

Ensures the truth of an expression involving one or more parameters to the calling method.

public static void
checkArgument(boolean expression, String errorMessageTemplate, long p1, char p2)

Ensures the truth of an expression involving one or more parameters to the calling method.

public static void
checkArgument(boolean expression, String errorMessageTemplate, long p1, int p2)

Ensures the truth of an expression involving one or more parameters to the calling method.

public static void
checkArgument(boolean expression, String errorMessageTemplate, long p1, long p2)

Ensures the truth of an expression involving one or more parameters to the calling method.

public static void
checkArgument(boolean expression, String errorMessageTemplate, long p1, Object p2)

Ensures the truth of an expression involving one or more parameters to the calling method.

public static void
checkArgument(boolean expression, String errorMessageTemplate, Object p1, char p2)

Ensures the truth of an expression involving one or more parameters to the calling method.

public static void
checkArgument(boolean expression, String errorMessageTemplate, Object p1, int p2)

Ensures the truth of an expression involving one or more parameters to the calling method.

public static void
checkArgument(boolean expression, String errorMessageTemplate, Object p1, long p2)

Ensures the truth of an expression involving one or more parameters to the calling method.

public static void
checkArgument(boolean expression, String errorMessageTemplate, Object p1, Object p2)

Ensures the truth of an expression involving one or more parameters to the calling method.

public static void
checkArgument(boolean expression, String errorMessageTemplate, Object p1, Object p2, Object p3)

Ensures the truth of an expression involving one or more parameters to the calling method.

public static void
checkArgument(boolean expression, String errorMessageTemplate, Object p1, Object p2, Object p3, Object p4)

Ensures the truth of an expression involving one or more parameters to the calling method.

public static int

Returns:

the value of index
checkElementIndex(int
a user-supplied index identifying an element of an array, list or string
index, int
the size of that array, list or string
size)

Ensures that index specifies a valid element in an array, list or string of size size.

public static int

Returns:

the value of index
checkElementIndex(int
a user-supplied index identifying an element of an array, list or string
index, int
the size of that array, list or string
size, String
the text to use to describe this index in an error message
desc)

Ensures that index specifies a valid element in an array, list or string of size size.

public static <T> T

Returns:

the non-null reference that was validated
checkNotNull(T
an object reference
reference)

Ensures that an object reference passed as a parameter to the calling method is not null.

public static <T> T

Returns:

the non-null reference that was validated
checkNotNull(T
an object reference
reference, Object
the exception message to use if the check fails; will be converted to a string using String#valueOf(Object)
errorMessage)

Ensures that an object reference passed as a parameter to the calling method is not null.

public static <T> T

Returns:

the non-null reference that was validated
checkNotNull(T
an object reference
reference, String
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.
errorMessageTemplate, @Nullable Object...
the arguments to be substituted into the message template. Arguments are converted to strings using String#valueOf(Object).
errorMessageArgs)

Ensures that an object reference passed as a parameter to the calling method is not null.

public static <T> T
checkNotNull(T reference, String errorMessageTemplate, char p1)

Ensures that an object reference passed as a parameter to the calling method is not null.

public static <T> T
checkNotNull(T reference, String errorMessageTemplate, int p1)

Ensures that an object reference passed as a parameter to the calling method is not null.

public static <T> T
checkNotNull(T reference, String errorMessageTemplate, long p1)

Ensures that an object reference passed as a parameter to the calling method is not null.

public static <T> T
checkNotNull(T reference, String errorMessageTemplate, Object p1)

Ensures that an object reference passed as a parameter to the calling method is not null.

public static <T> T
checkNotNull(T reference, String errorMessageTemplate, char p1, char p2)

Ensures that an object reference passed as a parameter to the calling method is not null.

public static <T> T
checkNotNull(T reference, String errorMessageTemplate, char p1, int p2)

Ensures that an object reference passed as a parameter to the calling method is not null.

public static <T> T
checkNotNull(T reference, String errorMessageTemplate, char p1, long p2)

Ensures that an object reference passed as a parameter to the calling method is not null.

public static <T> T
checkNotNull(T reference, String errorMessageTemplate, char p1, Object p2)

Ensures that an object reference passed as a parameter to the calling method is not null.

public static <T> T
checkNotNull(T reference, String errorMessageTemplate, int p1, char p2)

Ensures that an object reference passed as a parameter to the calling method is not null.

public static <T> T
checkNotNull(T reference, String errorMessageTemplate, int p1, int p2)

Ensures that an object reference passed as a parameter to the calling method is not null.

public static <T> T
checkNotNull(T reference, String errorMessageTemplate, int p1, long p2)

Ensures that an object reference passed as a parameter to the calling method is not null.

public static <T> T
checkNotNull(T reference, String errorMessageTemplate, int p1, Object p2)

Ensures that an object reference passed as a parameter to the calling method is not null.

public static <T> T
checkNotNull(T reference, String errorMessageTemplate, long p1, char p2)

Ensures that an object reference passed as a parameter to the calling method is not null.

public static <T> T
checkNotNull(T reference, String errorMessageTemplate, long p1, int p2)

Ensures that an object reference passed as a parameter to the calling method is not null.

public static <T> T
checkNotNull(T reference, String errorMessageTemplate, long p1, long p2)

Ensures that an object reference passed as a parameter to the calling method is not null.

public static <T> T
checkNotNull(T reference, String errorMessageTemplate, long p1, Object p2)

Ensures that an object reference passed as a parameter to the calling method is not null.

public static <T> T
checkNotNull(T reference, String errorMessageTemplate, Object p1, char p2)

Ensures that an object reference passed as a parameter to the calling method is not null.

public static <T> T
checkNotNull(T reference, String errorMessageTemplate, Object p1, int p2)

Ensures that an object reference passed as a parameter to the calling method is not null.

public static <T> T
checkNotNull(T reference, String errorMessageTemplate, Object p1, long p2)

Ensures that an object reference passed as a parameter to the calling method is not null.

public static <T> T
checkNotNull(T reference, String errorMessageTemplate, Object p1, Object p2)

Ensures that an object reference passed as a parameter to the calling method is not null.

public static <T> T
checkNotNull(T reference, String errorMessageTemplate, Object p1, Object p2, Object p3)

Ensures that an object reference passed as a parameter to the calling method is not null.

public static <T> T
checkNotNull(T reference, String errorMessageTemplate, Object p1, Object p2, Object p3, Object p4)

Ensures that an object reference passed as a parameter to the calling method is not null.

public static int

Returns:

the value of index
checkPositionIndex(int
a user-supplied index identifying a position in an array, list or string
index, int
the size of that array, list or string
size)

Ensures that index specifies a valid position in an array, list or string of size size.

public static int

Returns:

the value of index
checkPositionIndex(int
a user-supplied index identifying a position in an array, list or string
index, int
the size of that array, list or string
size, String
the text to use to describe this index in an error message
desc)

Ensures that index specifies a valid position in an array, list or string of size size.

public static void
checkPositionIndexes(int
a user-supplied index identifying a starting position in an array, list or string
start, int
a user-supplied index identifying an ending position in an array, list or string
end, int
the size of that array, list or string
size)

Ensures that start and end specify valid positions in an array, list or string of size size, and are in order.

public static void
checkState(boolean
a boolean expression
expression)

Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method.

public static void
checkState(boolean
a boolean expression
expression, Object
the exception message to use if the check fails; will be converted to a string using String#valueOf(Object)
errorMessage)

Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method.

public static void
checkState(boolean
a boolean expression
expression, String
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.
errorMessageTemplate, @Nullable Object...
the arguments to be substituted into the message template. Arguments are converted to strings using String#valueOf(Object).
errorMessageArgs)

Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method.

public static void
checkState(boolean expression, String errorMessageTemplate, char p1)

Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method.

public static void
checkState(boolean expression, String errorMessageTemplate, int p1)

Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method.

public static void
checkState(boolean expression, String errorMessageTemplate, long p1)

Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method.

public static void
checkState(boolean expression, String errorMessageTemplate, Object p1)

Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method.

public static void
checkState(boolean expression, String errorMessageTemplate, char p1, char p2)

Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method.

public static void
checkState(boolean expression, String errorMessageTemplate, char p1, int p2)

Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method.

public static void
checkState(boolean expression, String errorMessageTemplate, char p1, long p2)

Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method.

public static void
checkState(boolean expression, String errorMessageTemplate, char p1, Object p2)

Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method.

public static void
checkState(boolean expression, String errorMessageTemplate, int p1, char p2)

Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method.

public static void
checkState(boolean expression, String errorMessageTemplate, int p1, int p2)

Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method.

public static void
checkState(boolean expression, String errorMessageTemplate, int p1, long p2)

Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method.

public static void
checkState(boolean expression, String errorMessageTemplate, int p1, Object p2)

Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method.

public static void
checkState(boolean expression, String errorMessageTemplate, long p1, char p2)

Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method.

public static void
checkState(boolean expression, String errorMessageTemplate, long p1, int p2)

Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method.

public static void
checkState(boolean expression, String errorMessageTemplate, long p1, long p2)

Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method.

public static void
checkState(boolean expression, String errorMessageTemplate, long p1, Object p2)

Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method.

public static void
checkState(boolean expression, String errorMessageTemplate, Object p1, char p2)

Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method.

public static void
checkState(boolean expression, String errorMessageTemplate, Object p1, int p2)

Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method.

public static void
checkState(boolean expression, String errorMessageTemplate, Object p1, long p2)

Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method.

public static void
checkState(boolean expression, String errorMessageTemplate, Object p1, Object p2)

Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method.

public static void
checkState(boolean expression, String errorMessageTemplate, Object p1, Object p2, Object p3)

Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method.

public static void
checkState(boolean expression, String errorMessageTemplate, Object p1, Object p2, Object p3, Object p4)

Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method.

Inherited from java.lang.Object:
cloneequalsfinalizegetClasshashCodenotifynotifyAlltoStringwaitwaitwait