Preconditions

Class Overview

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);
 }
 }

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 java.util.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 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 java.util.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.

Summary

[Expand] Inherited Methods
From class java.lang.Object Object clone() boolean equals(Object arg0) void finalize() final Class<?> getClass() int hashCode() final void notify() final void notifyAll() String toString() final void wait(long arg0, int arg1) final void wait(long arg0) final void wait()