com.google.common.base

Class Preconditions

java.lang.Object

com.google.common.base.Preconditions

@GwtCompatible
public final class Preconditions
extends Object

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 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 Objects.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 Formatter specifiers.

More information

See the Guava User Guide on using Preconditions.

Since:

2.0 (imported from Google Collections Library)

Author:

Kevin Bourrillion

Method Summary

Methods

Modifier and Type	Method and Description
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,
                 @Nullable
                 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,
                 @Nullable
                 String errorMessageTemplate,
                 @Nullable
                 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,
              @Nullable
              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,
              @Nullable
              String errorMessageTemplate,
              @Nullable
              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,
                 @Nullable
                 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,
                 @Nullable
                 String errorMessageTemplate,
                 @Nullable
                 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,
                    @Nullable
                    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,
                     @Nullable
                     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