public final class

Preconditions

extends Object
java.lang.Object
   ↳ com.google.gdata.util.common.base.Preconditions

Class Overview

Simple static methods to be called at the start of your own methods to verify correct arguments and state. This allows constructs such as 

     if (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 an assert or a JUnit assertTrue() call.

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.

Note: The methods of the Preconditions class are highly unusual in one way: they are supposed to throw exceptions, and promise in their specifications to do so even when given perfectly valid input. That is, null is a valid parameter to the method checkNotNull(Object) -- and technically this parameter could be even marked as Nullable -- yet the method will still throw an exception anyway, because that's what its contract says to do.

Summary

Public Methods
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 <T extends Iterable<?>> T checkContentsNotNull(T iterable, String errorMessageTemplate, Object... errorMessageArgs)
Ensures that an Iterable object passed as a parameter to the calling method is not null and contains no null elements.
static <T extends Iterable<?>> T checkContentsNotNull(T iterable, Object errorMessage)
Ensures that an Iterable object passed as a parameter to the calling method is not null and contains no null elements.
static <T extends Iterable<?>> T checkContentsNotNull(T iterable)
Ensures that an Iterable object passed as a parameter to the calling method is not null and contains no null elements.
static void checkElementIndex(int index, int size, String desc)
Ensures that index specifies a valid element in an array, list or string of size size.
static void 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)
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 checkPositionIndex(int index, int size, String desc)
Ensures that index specifies a valid position in an array, list or string of size size.
static void 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, 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, 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)
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)

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 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, 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 T checkContentsNotNull (T iterable, String errorMessageTemplate, Object... errorMessageArgs)

Ensures that an Iterable object passed as a parameter to the calling method is not null and contains no null elements.

Parameters
iterable The iterable to check the contents of
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 iterable reference just validated
Throws
NullPointerException if iterable is null or contains at least one null element

public static T checkContentsNotNull (T iterable, Object errorMessage)

Ensures that an Iterable object passed as a parameter to the calling method is not null and contains no null elements.

Parameters
iterable The iterable to check the contents of
errorMessage The exception message to use if the check fails; will be converted to a string using valueOf(Object)
Returns
  • the non-null iterable reference just validated
Throws
NullPointerException if iterable is null or contains at least one null element

public static T checkContentsNotNull (T iterable)

Ensures that an Iterable object passed as a parameter to the calling method is not null and contains no null elements.

Parameters
iterable The iterable to check the contents of
Returns
  • the non-null iterable reference just validated
Throws
NullPointerException if iterable is null or contains at least one null element

public static void 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
Throws
IndexOutOfBoundsException if index is negative or is not less than size
IllegalArgumentException if size is negative

public static void 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
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)

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 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 void 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
Throws
IndexOutOfBoundsException if index is negative or is greater than size
IllegalArgumentException if size is negative

public static void 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
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, 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, 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)

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