com.google.common.base
Class Preconditions

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

public final class Preconditions
extends java.lang.Object

Contains 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, perhaps using AssertionError instead.

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.

Author:

Kevin Bourrillion

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, java.lang.Object errorMessage) Ensures the truth of an expression involving one or more parameters to the calling method.
static void	checkArgument(boolean expression, java.lang.String errorMessageFormat, java.lang.Object... errorMessageArgs) Ensures the truth of an expression involving one or more parameters to the calling method.
static <T extends java.lang.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 java.lang.Iterable<?>> T	checkContentsNotNull(T iterable, java.lang.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 java.lang.Iterable<?>> T	checkContentsNotNull(T iterable, java.lang.String errorMessageFormat, java.lang.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> T	checkNotNull(T reference) Ensures that an object reference passed as a parameter to the calling method is not null, throwing a NullPointerException if it is.
static <T> T	checkNotNull(T reference, java.lang.Object errorMessage) Ensures that an object reference passed as a parameter to the calling method is not null, throwing a NullPointerException if it is.
static <T> T	checkNotNull(T reference, java.lang.String errorMessageFormat, java.lang.Object... errorMessageArgs) Ensures that an object reference passed as a parameter to the calling method is not null, throwing a NullPointerException if it is.
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, java.lang.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, java.lang.String errorMessageFormat, java.lang.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:

java.lang.IllegalArgumentException - if expression is false

checkArgument

public static void checkArgument(boolean expression,
                                 java.lang.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) only if needed

Throws:

java.lang.IllegalArgumentException - if expression is false

checkArgument

public static void checkArgument(boolean expression,
                                 java.lang.String errorMessageFormat,
                                 java.lang.Object... errorMessageArgs)

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

Parameters:

expression - a boolean expression

errorMessageFormat - the format string for the desired error message

errorMessageArgs - the arguments referenced by the format specifiers in errorMessageFormat.

Throws:

java.lang.IllegalArgumentException - if expression is false

java.lang.NullPointerException - if the check fails and either errorMessageFormat 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:

java.lang.IllegalStateException - if expression is false

checkState

public static void checkState(boolean expression,
                              java.lang.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) only if needed

Throws:

java.lang.IllegalStateException - if expression is false

checkState

public static void checkState(boolean expression,
                              java.lang.String errorMessageFormat,
                              java.lang.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

errorMessageFormat - the format string for the desired error message

errorMessageArgs - the arguments referenced by the format specifiers in errorMessageFormat.

Throws:

java.lang.IllegalStateException - if expression is false

java.lang.NullPointerException - if the check fails and either errorMessageFormat 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, throwing a NullPointerException if it is.

Parameters:

reference - an object reference

Returns:

the non-null reference that was validated

Throws:

java.lang.NullPointerException - if reference is null

checkNotNull

public static <T> T checkNotNull(T reference,
                                 java.lang.Object errorMessage)

Ensures that an object reference passed as a parameter to the calling method is not null, throwing a NullPointerException if it is.

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) only if needed

Returns:

the non-null reference that was validated

Throws:

java.lang.NullPointerException - if reference is null

checkNotNull

public static <T> T checkNotNull(T reference,
                                 java.lang.String errorMessageFormat,
                                 java.lang.Object... errorMessageArgs)

Ensures that an object reference passed as a parameter to the calling method is not null, throwing a NullPointerException if it is.

Parameters:

reference - an object reference

errorMessageFormat - the format string for the desired error message

errorMessageArgs - the arguments referenced by the format specifiers in errorMessageFormat.

Returns:

the non-null reference that was validated

Throws:

java.lang.NullPointerException - if reference is null

checkContentsNotNull

public static <T extends java.lang.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 - any Iterable object

Returns:

the non-null iterable reference just validated

Throws:

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

checkContentsNotNull

public static <T extends java.lang.Iterable<?>> T checkContentsNotNull(T iterable,
                                                                       java.lang.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 - any Iterable object

errorMessage - the exception message to use if the check fails; will be converted to a string using String.valueOf(Object) only if needed

Returns:

the non-null iterable reference just validated

Throws:

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

checkContentsNotNull

public static <T extends java.lang.Iterable<?>> T checkContentsNotNull(T iterable,
                                                                       java.lang.String errorMessageFormat,
                                                                       java.lang.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 - any Iterable object

errorMessageFormat - the format string for the desired error message

errorMessageArgs - the arguments referenced by the format specifiers in errorMessageFormat.

Returns:

the non-null iterable reference just validated

Throws:

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