/*
* Copyright (C) 2013 The Guava Authors
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
* in compliance with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software distributed under the License
* is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
* or implied. See the License for the specific language governing permissions and limitations under
* the License.
*/
package com.google.common.base;
import static com.google.common.base.Preconditions.format;
import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import javax.annotation.Nullable;
/**
* Static convenience methods that serve the same purpose as Java language
* <a href="http://docs.oracle.com/javase/7/docs/technotes/guides/language/assert.html">
* assertions</a>, 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: <pre> {@code
*
* 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());}</pre>
*
* <h3>Comparison to alternatives</h3>
*
* <p><b>Note:</b> In some cases the differences explained below can be subtle. When it's unclear
* which approach to use, <b>don't worry</b> too much about it; just pick something that seems
* reasonable and it will be fine.
*
* <ul>
* <li>If checking whether the <i>caller</i> has violated your method or constructor's contract
* (such as by passing an invalid argument), use the utilities of the {@link Preconditions}
* class instead.
*
* <li>If checking an <i>impossible</i> condition (which <i>cannot</i> happen unless your own class
* or its <i>trusted</i> 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."
*
* <li>An explicit {@code if/throw} (as illustrated below) is always acceptable; we still recommend
* using our {@link VerifyException} exception type. Throwing a plain {@link RuntimeException}
* is frowned upon.
*
* <li>Use of {@link java.util.Objects#requireNonNull(Object)} is generally discouraged, since
* {@link #verifyNotNull(Object)} and {@link Preconditions#checkNotNull(Object)} perform the
* same function with more clarity.
* </ul>
*
* <h3>Warning about performance</h3>
*
* <p>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: <pre> {@code
*
* Bill bill = remoteService.getLastUnpaidBill();
* if (bill.status() != Status.UNPAID) {
* throw new VerifyException("Unexpected bill status: " + bill.status());
* }}</pre>
*
* <h3>Only {@code %s} is supported</h3>
*
* <p>As with {@link Preconditions} error message template strings, only the {@code "%s"} specifier
* is supported, not the full range of {@link java.util.Formatter} specifiers. However, note that
* if the number of arguments does not match the number of occurrences of {@code "%s"} in the
* format string, {@code 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.
*
* <h3>More information</h3>
*
* See
* <a href="http://code.google.com/p/guava-libraries/wiki/ConditionalFailuresExplained">Conditional
* failures explained</a> in the Guava User Guide for advice on when this class should be used.
*
* @since 17.0
*/
@Beta
@GwtCompatible
public final class Verify {
/**
* Ensures that {@code expression} is {@code true}, throwing a {@code VerifyException} with no
* message otherwise.
*/
public static void verify(boolean expression) {
if (!expression) {
throw new VerifyException();
}
}
/**
* Ensures that {@code expression} is {@code true}, throwing a {@code VerifyException} with a
* custom message otherwise.
*
* @param expression a boolean expression
* @param errorMessageTemplate a template for the exception message should the
* check fail. The message is formed by replacing each {@code %s}
* placeholder in the template with an argument. These are matched by
* position - the first {@code %s} gets {@code errorMessageArgs[0]}, etc.
* Unmatched arguments will be appended to the formatted message in square
* braces. Unmatched placeholders will be left as-is.
* @param errorMessageArgs the arguments to be substituted into the message
* template. Arguments are converted to strings using
* {@link String#valueOf(Object)}.
* @throws VerifyException if {@code expression} is {@code false}
*/
public static void verify(
boolean expression,
@Nullable String errorMessageTemplate,
@Nullable Object... errorMessageArgs) {
if (!expression) {
throw new VerifyException(format(errorMessageTemplate, errorMessageArgs));
}
}
/**
* Ensures that {@code reference} is non-null, throwing a {@code VerifyException} with a default
* message otherwise.
*
* @return {@code reference}, guaranteed to be non-null, for convenience
*/
public static <T> T verifyNotNull(@Nullable T reference) {
return verifyNotNull(reference, "expected a non-null reference");
}
/**
* Ensures that {@code reference} is non-null, throwing a {@code VerifyException} with a custom
* message otherwise.
*
* @param errorMessageTemplate a template for the exception message should the
* check fail. The message is formed by replacing each {@code %s}
* placeholder in the template with an argument. These are matched by
* position - the first {@code %s} gets {@code errorMessageArgs[0]}, etc.
* Unmatched arguments will be appended to the formatted message in square
* braces. Unmatched placeholders will be left as-is.
* @param errorMessageArgs the arguments to be substituted into the message
* template. Arguments are converted to strings using
* {@link String#valueOf(Object)}.
* @return {@code reference}, guaranteed to be non-null, for convenience
*/
public static <T> T verifyNotNull(
@Nullable T reference,
@Nullable String errorMessageTemplate,
@Nullable Object... errorMessageArgs) {
verify(reference != null, errorMessageTemplate, errorMessageArgs);
return reference;
}
// TODO(kevinb): consider <T> T verifySingleton(Iterable<T>) to take over for
// Iterables.getOnlyElement()
private Verify() {}
}