com.google.common.base
Class Preconditions

java.lang.Object
  extended by com.google.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.

Warning: only the "%s" specifier is recognized as a placeholder in these messages, not the full range of String.format(String, Object[]) specifiers.

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.

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

checkElementIndex

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

checkElementIndex

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

checkPositionIndex

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

checkPositionIndex

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

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