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 (that is, whether its preconditions were met).

If the precondition is not met, the Preconditions method throws an unchecked exception of a specified type, which helps the method in which the exception was thrown communicate that its caller has made a mistake. This allows constructs such as 


 public static double sqrt(double value) {
   if (value < 0) {
     throw new IllegalArgumentException("input is negative: " + value);
   }
   // calculate square root
 }

to be replaced with the more compact 


 public static double sqrt(double value) {
   checkArgument(value >= 0, "input is negative: %s", value);
   // calculate square root
 }

so that a hypothetical bad caller of this method, such as: 


 void exampleBadCaller() {
   double d = sqrt(-1.0);
 }

would be flagged as having called sqrt() with an illegal argument.

Performance

Avoid passing message arguments that are expensive to compute; your code will always compute them, even though they usually won't be needed. If you have such arguments, use the conventional if/throw idiom instead.

Depending on your message arguments, memory may be allocated for boxing and varargs array creation. However, the methods of this class have a large number of overloads that prevent such allocations in many common cases.

The message string is not formatted unless the exception will be thrown, so the cost of the string formatting itself should not be a concern.

As with any performance concerns, you should consider profiling your code (in a production environment if possible) before spending a lot of effort on tweaking a particular element.

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. Notably, Verify offers assertions similar to those in this class for non-precondition checks.

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

Preconditions uses Strings.lenientFormat(java.lang.String, java.lang.Object...) to format error message template strings. This only supports the "%s" specifier, not the full range of Formatter specifiers. However, note that if the number of arguments does not match the number of occurrences of "%s" in the format string, Preconditions will still behave as expected, and will still include all argument values in the error message; the message will simply not be formatted exactly as intended.

More information

See the Guava User Guide on using Preconditions.

Since:
2.0
Author:
Kevin Bourrillion

  • Method Summary

    Modifier and Type
    Method
    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, @Nullable Object errorMessage)
    Ensures the truth of an expression involving one or more parameters to the calling method.
    static void
    checkArgument(boolean expression, @Nullable String errorMessageTemplate, @Nullable Object p1, @Nullable Object p2)
    Ensures the truth of an expression involving one or more parameters to the calling method.
    static void
    checkArgument(boolean expression, String errorMessageTemplate, char p1)
    Ensures the truth of an expression involving one or more parameters to the calling method.
    static void
    checkArgument(boolean expression, String errorMessageTemplate, char p1, char p2)
    Ensures the truth of an expression involving one or more parameters to the calling method.
    static void
    checkArgument(boolean expression, String errorMessageTemplate, char p1, int p2)
    Ensures the truth of an expression involving one or more parameters to the calling method.
    static void
    checkArgument(boolean expression, String errorMessageTemplate, char p1, long p2)
    Ensures the truth of an expression involving one or more parameters to the calling method.
    static void
    checkArgument(boolean expression, String errorMessageTemplate, char p1, @Nullable Object p2)
    Ensures the truth of an expression involving one or more parameters to the calling method.
    static void
    checkArgument(boolean expression, String errorMessageTemplate, int p1)
    Ensures the truth of an expression involving one or more parameters to the calling method.
    static void
    checkArgument(boolean expression, String errorMessageTemplate, int p1, char p2)
    Ensures the truth of an expression involving one or more parameters to the calling method.
    static void
    checkArgument(boolean expression, String errorMessageTemplate, int p1, int p2)
    Ensures the truth of an expression involving one or more parameters to the calling method.
    static void
    checkArgument(boolean expression, String errorMessageTemplate, int p1, long p2)
    Ensures the truth of an expression involving one or more parameters to the calling method.
    static void
    checkArgument(boolean expression, String errorMessageTemplate, int p1, @Nullable Object p2)
    Ensures the truth of an expression involving one or more parameters to the calling method.
    static void
    checkArgument(boolean expression, String errorMessageTemplate, long p1)
    Ensures the truth of an expression involving one or more parameters to the calling method.
    static void
    checkArgument(boolean expression, String errorMessageTemplate, long p1, char p2)
    Ensures the truth of an expression involving one or more parameters to the calling method.
    static void
    checkArgument(boolean expression, String errorMessageTemplate, long p1, int p2)
    Ensures the truth of an expression involving one or more parameters to the calling method.
    static void
    checkArgument(boolean expression, String errorMessageTemplate, long p1, long p2)
    Ensures the truth of an expression involving one or more parameters to the calling method.
    static void
    checkArgument(boolean expression, String errorMessageTemplate, long p1, @Nullable Object p2)
    Ensures the truth of an expression involving one or more parameters to the calling method.
    static void
    checkArgument(boolean expression, String errorMessageTemplate, @Nullable Object p1)
    Ensures the truth of an expression involving one or more parameters to the calling method.
    static void
    checkArgument(boolean expression, String errorMessageTemplate, @Nullable Object @Nullable ... errorMessageArgs)
    Ensures the truth of an expression involving one or more parameters to the calling method.
    static void
    checkArgument(boolean expression, String errorMessageTemplate, @Nullable Object p1, char p2)
    Ensures the truth of an expression involving one or more parameters to the calling method.
    static void
    checkArgument(boolean expression, String errorMessageTemplate, @Nullable Object p1, int p2)
    Ensures the truth of an expression involving one or more parameters to the calling method.
    static void
    checkArgument(boolean expression, String errorMessageTemplate, @Nullable Object p1, long p2)
    Ensures the truth of an expression involving one or more parameters to the calling method.
    static void
    checkArgument(boolean expression, String errorMessageTemplate, @Nullable Object p1, @Nullable Object p2, @Nullable Object p3)
    Ensures the truth of an expression involving one or more parameters to the calling method.
    static void
    checkArgument(boolean expression, String errorMessageTemplate, @Nullable Object p1, @Nullable Object p2, @Nullable Object p3, @Nullable Object p4)
    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(@Nullable T reference)
    Ensures that an object reference passed as a parameter to the calling method is not null.
    static <T> T
    checkNotNull(@Nullable T reference, @Nullable Object errorMessage)
    Ensures that an object reference passed as a parameter to the calling method is not null.
    static <T> T
    checkNotNull(@Nullable T reference, String errorMessageTemplate, char p1)
    Ensures that an object reference passed as a parameter to the calling method is not null.
    static <T> T
    checkNotNull(@Nullable T reference, String errorMessageTemplate, char p1, char p2)
    Ensures that an object reference passed as a parameter to the calling method is not null.
    static <T> T
    checkNotNull(@Nullable T reference, String errorMessageTemplate, char p1, int p2)
    Ensures that an object reference passed as a parameter to the calling method is not null.
    static <T> T
    checkNotNull(@Nullable T reference, String errorMessageTemplate, char p1, long p2)
    Ensures that an object reference passed as a parameter to the calling method is not null.
    static <T> T
    checkNotNull(@Nullable T reference, String errorMessageTemplate, char p1, @Nullable Object p2)
    Ensures that an object reference passed as a parameter to the calling method is not null.
    static <T> T
    checkNotNull(@Nullable T reference, String errorMessageTemplate, int p1)
    Ensures that an object reference passed as a parameter to the calling method is not null.
    static <T> T
    checkNotNull(@Nullable T reference, String errorMessageTemplate, int p1, char p2)
    Ensures that an object reference passed as a parameter to the calling method is not null.
    static <T> T
    checkNotNull(@Nullable T reference, String errorMessageTemplate, int p1, int p2)
    Ensures that an object reference passed as a parameter to the calling method is not null.
    static <T> T
    checkNotNull(@Nullable T reference, String errorMessageTemplate, int p1, long p2)
    Ensures that an object reference passed as a parameter to the calling method is not null.
    static <T> T
    checkNotNull(@Nullable T reference, String errorMessageTemplate, int p1, @Nullable Object p2)
    Ensures that an object reference passed as a parameter to the calling method is not null.
    static <T> T
    checkNotNull(@Nullable T reference, String errorMessageTemplate, long p1)
    Ensures that an object reference passed as a parameter to the calling method is not null.
    static <T> T
    checkNotNull(@Nullable T reference, String errorMessageTemplate, long p1, char p2)
    Ensures that an object reference passed as a parameter to the calling method is not null.
    static <T> T
    checkNotNull(@Nullable T reference, String errorMessageTemplate, long p1, int p2)
    Ensures that an object reference passed as a parameter to the calling method is not null.
    static <T> T
    checkNotNull(@Nullable T reference, String errorMessageTemplate, long p1, long p2)
    Ensures that an object reference passed as a parameter to the calling method is not null.
    static <T> T
    checkNotNull(@Nullable T reference, String errorMessageTemplate, long p1, @Nullable Object p2)
    Ensures that an object reference passed as a parameter to the calling method is not null.
    static <T> T
    checkNotNull(@Nullable T reference, String errorMessageTemplate, @Nullable Object p1)
    Ensures that an object reference passed as a parameter to the calling method is not null.
    static <T> T
    checkNotNull(@Nullable T reference, String errorMessageTemplate, @Nullable Object @Nullable ... errorMessageArgs)
    Ensures that an object reference passed as a parameter to the calling method is not null.
    static <T> T
    checkNotNull(@Nullable T reference, String errorMessageTemplate, @Nullable Object p1, char p2)
    Ensures that an object reference passed as a parameter to the calling method is not null.
    static <T> T
    checkNotNull(@Nullable T reference, String errorMessageTemplate, @Nullable Object p1, int p2)
    Ensures that an object reference passed as a parameter to the calling method is not null.
    static <T> T
    checkNotNull(@Nullable T reference, String errorMessageTemplate, @Nullable Object p1, long p2)
    Ensures that an object reference passed as a parameter to the calling method is not null.
    static <T> T
    checkNotNull(@Nullable T reference, String errorMessageTemplate, @Nullable Object p1, @Nullable Object p2)
    Ensures that an object reference passed as a parameter to the calling method is not null.
    static <T> T
    checkNotNull(@Nullable T reference, String errorMessageTemplate, @Nullable Object p1, @Nullable Object p2, @Nullable Object p3)
    Ensures that an object reference passed as a parameter to the calling method is not null.
    static <T> T
    checkNotNull(@Nullable T reference, String errorMessageTemplate, @Nullable Object p1, @Nullable Object p2, @Nullable Object p3, @Nullable Object p4)
    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 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, @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.
    static void
    checkState(boolean expression, @Nullable String errorMessageTemplate, @Nullable Object @Nullable ... 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, String errorMessageTemplate, char p1)
    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, char p1, char p2)
    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, char p1, int p2)
    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, char p1, long p2)
    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, char p1, @Nullable Object p2)
    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, int p1)
    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, int p1, char p2)
    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, int p1, int p2)
    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, int p1, long p2)
    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, int p1, @Nullable Object p2)
    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, long p1)
    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, long p1, char p2)
    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, long p1, int p2)
    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, long p1, long p2)
    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, long p1, @Nullable Object p2)
    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, @Nullable Object p1)
    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, @Nullable Object p1, char p2)
    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, @Nullable Object p1, int p2)
    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, @Nullable Object p1, long p2)
    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, @Nullable Object p1, @Nullable Object p2)
    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, @Nullable Object p1, @Nullable Object p2, @Nullable Object p3)
    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, @Nullable Object p1, @Nullable Object p2, @Nullable Object p3, @Nullable Object p4)
    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