com.google.gdata.util.common.base
Class Preconditions

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

public final class Preconditions
extends Object

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.

This class may be used with the Google Web Toolkit (GWT).

Method Summary

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) 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, 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 void	checkElementIndex(int index, int size) Ensures that index specifies a valid element in an array, list or string of size size.
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 <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	checkPositionIndex(int index, int size) Ensures that index specifies a valid position in an array, list or string of size size.
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	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) 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, 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.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

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 - if expression is false

checkArgument

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 String.valueOf(Object)

Throws:

IllegalArgumentException - if expression 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 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 String.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)

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 - if expression is false

checkState

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 String.valueOf(Object)

Throws:

IllegalStateException - if expression is false

checkState

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 String.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)

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 - if reference is null

checkNotNull

public static <T> 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 String.valueOf(Object)

Returns:

the non-null reference that was validated

Throws:

NullPointerException - if reference 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 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 String.valueOf(Object).

Returns:

the non-null reference that was validated

Throws:

NullPointerException - if reference is null

checkContentsNotNull

public 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.

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

checkContentsNotNull

public 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.

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 String.valueOf(Object)

Returns:

the non-null iterable reference just validated

Throws:

NullPointerException - if iterable is null or contains at least one null element

checkContentsNotNull

public 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.

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 String.valueOf(Object).

Returns:

the non-null iterable reference just validated

Throws:

NullPointerException - if iterable is null or contains at least one null element

checkElementIndex

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

checkElementIndex

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

checkPositionIndex

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

checkPositionIndex

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

checkPositionIndexes

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