public final class

Preconditions

extends Object
java.lang.Object
   ↳ com.facebook.common.internal.Preconditions

Class Overview

Static convenience methods that help a method or constructor check whether it was invoked correctly (whether its preconditions have been met). These methods generally accept a 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.

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 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.

java.util.Objects.requireNonNull()

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

In Preconditions error message template strings, only the "%s" specifier is supported, 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.

Summary

Public Methods
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 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)
Ensures the truth of an expression involving one or more parameters to the calling method.
static int checkElementIndex(int index, int size, String desc)
Ensures that index specifies a valid element in an array, list or string of size size.
static int checkElementIndex(int index, int size)
Ensures that index specifies a valid element in an array, list or string of size size.
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 <T> T checkNotNull(T reference)
Ensures that an object reference passed as a parameter to the calling method is not null.
static int checkPositionIndex(int index, int size, String desc)
Ensures that index specifies a valid position in an array, list or string of size size.
static int checkPositionIndex(int index, int size)
Ensures that index specifies a valid position in an array, list or string of size size.
static void checkPositionIndexes(int start, int end, int size)
Ensures that start and end specify a valid positions in an array, list or string of size size, and are in order.
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.
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.
[Expand]
Inherited Methods
From class java.lang.Object

Public Methods

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 expression
errorMessageTemplate 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 valueOf(Object).
Throws
IllegalArgumentException if expression is false
NullPointerException if the check fails and either errorMessageTemplate or errorMessageArgs is null (don't let this happen)

public static void checkArgument (boolean expression, Object errorMessage)

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

Parameters
expression a boolean expression
errorMessage the exception message to use if the check fails; will be converted to a string using valueOf(Object)
Throws
IllegalArgumentException if expression is false

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 if expression is false

public static int checkElementIndex (int index, int size, String desc)

Ensures that index specifies a valid element in an array, list or string of size size. An element index may range from zero, inclusive, to size, exclusive.

Parameters
index a user-supplied index identifying an element of an array, list or string
size the size of that array, list or string
desc the text to use to describe this index in an error message
Returns
  • the value of index
Throws
IndexOutOfBoundsException if index is negative or is not less than size
IllegalArgumentException if size is negative

public static int checkElementIndex (int index, int size)

Ensures that index specifies a valid element in an array, list or string of size size. An element index may range from zero, inclusive, to size, exclusive.

Parameters
index a user-supplied index identifying an element of an array, list or string
size the size of that array, list or string
Returns
  • the value of index
Throws
IndexOutOfBoundsException if index is negative or is not less than size
IllegalArgumentException if size is negative

public static T checkNotNull (T reference, Object errorMessage)

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

Parameters
reference an object reference
errorMessage the exception message to use if the check fails; will be converted to a string using valueOf(Object)
Returns
  • the non-null reference that was validated
Throws
NullPointerException if reference is null

public static 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 reference
errorMessageTemplate 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 valueOf(Object).
Returns
  • the non-null reference that was validated
Throws
NullPointerException if reference is null

public static 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 if reference is null

public static int checkPositionIndex (int index, int size, String desc)

Ensures that index specifies a valid position in an array, list or string of size size. A position index may range from zero to size, inclusive.

Parameters
index a user-supplied index identifying a position in an array, list or string
size the size of that array, list or string
desc the text to use to describe this index in an error message
Returns
  • the value of index
Throws
IndexOutOfBoundsException if index is negative or is greater than size
IllegalArgumentException if size is negative

public static int checkPositionIndex (int index, int size)

Ensures that index specifies a valid position in an array, list or string of size size. A position index may range from zero to size, inclusive.

Parameters
index a user-supplied index identifying a position in an array, list or string
size the size of that array, list or string
Returns
  • the value of index
Throws
IndexOutOfBoundsException if index is negative or is greater than size
IllegalArgumentException if size is negative

public static void checkPositionIndexes (int start, int end, int size)

Ensures that start and end specify a valid positions in an array, list or string of size size, and are in order. A position index may range from zero to size, inclusive.

Parameters
start a user-supplied index identifying a starting position in an array, list or string
end a user-supplied index identifying a ending position in an array, list or string
size the size of that array, list or string
Throws
IndexOutOfBoundsException if either index is negative or is greater than size, or if end is less than start
IllegalArgumentException if size is negative

public 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.

Parameters
expression a boolean expression
errorMessage the exception message to use if the check fails; will be converted to a string using valueOf(Object)
Throws
IllegalStateException if expression is false

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 expression
errorMessageTemplate 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 valueOf(Object).
Throws
IllegalStateException if expression is false
NullPointerException if the check fails and either errorMessageTemplate or errorMessageArgs is null (don't let this happen)

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 if expression is false