com.google.common.base

Class Verify

java.lang.Object

com.google.common.base.Verify

@Beta
@GwtCompatible
public final class Verify
extends Object

Static convenience methods that serve the same purpose as Java language assertions, except that they are always enabled. These methods should be used instead of Java assertions whenever there is a chance the check may fail "in real life". Example:

   Bill bill = remoteService.getLastUnpaidBill();

   // In case bug 12345 happens again we'd rather just die
   Verify.verify(bill.status() == Status.UNPAID,
       "Unexpected bill status: %s", bill.status());

Comparison to alternatives

Note: In some cases the differences explained below can be subtle. When it's unclear which approach to use, don't worry too much about it; just pick something that seems reasonable and it will be fine.

• If checking whether the caller has violated your method or constructor's contract (such as by passing an invalid argument), use the utilities of the Preconditions class instead.
• If checking an impossible condition (which cannot happen unless your own class or its trusted dependencies is badly broken), this is what ordinary Java assertions are for. Note that assertions are not enabled by default; they are essentially considered "compiled comments."
• An explicit if/throw (as illustrated above) is always acceptable; we still recommend using our VerifyException exception type. Throwing a plain RuntimeException is frowned upon.
• Use of Objects.requireNonNull(Object) is generally discouraged, since verifyNotNull(Object) and Preconditions.checkNotNull(Object) perform the same function with more clarity.

Warning about performance

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 verification succeeds and the message ends up unneeded. Performance-sensitive verification checks should continue to use usual form:

   Bill bill = remoteService.getLastUnpaidBill();
   if (bill.status() != Status.UNPAID) {
     throw new VerifyException("Unexpected bill status: " + bill.status());
   }

Only %s is supported

As with Preconditions error message template strings, only the "%s" specifier is supported, 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, Verify 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 Conditional failures explained in the Guava User Guide for advice on when this class should be used.

Since:

17.0

Method Summary

Methods

Modifier and Type	Method and Description
static void	verify(boolean expression) Ensures that expression is true, throwing a VerifyException with no message otherwise.
static void	verify(boolean expression, String errorMessageTemplate, Object... errorMessageArgs) Ensures that expression is true, throwing a VerifyException with a custom message otherwise.
static <T> T	verifyNotNull(T reference) Ensures that reference is non-null, throwing a VerifyException with a default message otherwise.
static <T> T	verifyNotNull(T reference, String errorMessageTemplate, Object... errorMessageArgs) Ensures that reference is non-null, throwing a VerifyException with a custom message otherwise.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

verify

public static void verify(boolean expression)

Ensures that expression is true, throwing a VerifyException with no message otherwise.

verify

public static void verify(boolean expression,
          @Nullable
          String errorMessageTemplate,
          @Nullable
          Object... errorMessageArgs)

Ensures that expression is true, throwing a VerifyException with a custom message otherwise.

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:

VerifyException - if expression is false

verifyNotNull

public static <T> T verifyNotNull(@Nullable
                  T reference)

Ensures that reference is non-null, throwing a VerifyException with a default message otherwise.

Returns:

reference, guaranteed to be non-null, for convenience

verifyNotNull

public static <T> T verifyNotNull(@Nullable
                  T reference,
                  @Nullable
                  String errorMessageTemplate,
                  @Nullable
                  Object... errorMessageArgs)

Ensures that reference is non-null, throwing a VerifyException with a custom message otherwise.

Parameters:

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:

reference, guaranteed to be non-null, for convenience