com.google.common.base.Preconditions Maven / Gradle / Ivy
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/*
* Copyright (C) 2007 Google Inc.
*
* 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 java.util.Collection;
import java.util.NoSuchElementException;
/**
* Simple static methods to be called at the start of your own methods to verify
* correct arguments and state. This allows constructs such as
*
* if (count <= 0) {
* throw new IllegalArgumentException("must be positive: " + count);
* }
*
* to be replaced with the more compact
*
* checkArgument(count > 0, "must be positive: %s", count);
*
* Note that the sense of the expression is inverted; with {@code Preconditions}
* you declare what you expect to be true, just as you do with an
*
* {@code assert} or a JUnit {@code assertTrue()} call.
*
* Take care not to confuse precondition checking with other similar types
* of checks! Precondition exceptions -- including those provided here, but also
* {@link IndexOutOfBoundsException}, {@link NoSuchElementException}, {@link
* UnsupportedOperationException} and others -- are used to signal that the
* calling method has made an error. This tells the caller that it should
* not have invoked the method when it did, with the arguments it did, or
* perhaps ever. Postcondition or other invariant failures should not
* throw these types of exceptions.
*
*
Note: The methods of the {@code Preconditions} class are highly
* unusual in one way: they are supposed to throw exceptions, and promise
* in their specifications to do so even when given perfectly valid input. That
* is, {@code null} is a valid parameter to the method {@link
* #checkNotNull(Object)} -- and technically this parameter could be even marked
* as {@link Nullable} -- yet the method will still throw an exception anyway,
* because that's what its contract says to do.
*
* @author Kevin Bourrillion
*/
public final class Preconditions {
private Preconditions() {}
/**
* Ensures the truth of an expression involving one or more parameters to the
* calling method.
*
* @param expression a boolean expression
* @throws IllegalArgumentException if {@code expression} is false
*/
public static void checkArgument(boolean expression) {
if (!expression) {
throw new IllegalArgumentException();
}
}
/**
* Ensures the truth of an expression involving one or more parameters to the
* calling method.
*
* @param expression a boolean expression
* @param errorMessage the exception message to use if the check fails; will
* be converted to a string using {@link String#valueOf(Object)}
* @throws IllegalArgumentException if {@code expression} is false
*/
public static void checkArgument(boolean expression, Object errorMessage) {
if (!expression) {
throw new IllegalArgumentException(String.valueOf(errorMessage));
}
}
/**
* Ensures the truth of an expression involving one or more parameters to the
* calling method.
*
* @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 IllegalArgumentException if {@code expression} is false
* @throws NullPointerException if the check fails and either {@code
* errorMessageTemplate} or {@code errorMessageArgs} is null (don't let
* this happen)
*/
public static void checkArgument(boolean expression,
String errorMessageTemplate, Object... errorMessageArgs) {
if (!expression) {
throw new IllegalArgumentException(
format(errorMessageTemplate, errorMessageArgs));
}
}
/**
* Ensures the truth of an expression involving the state of the calling
* instance, but not involving any parameters to the calling method.
*
* @param expression a boolean expression
* @throws IllegalStateException if {@code expression} is false
*/
public static void checkState(boolean expression) {
if (!expression) {
throw new IllegalStateException();
}
}
/**
* Ensures the truth of an expression involving the state of the calling
* instance, but not involving any parameters to the calling method.
*
* @param expression a boolean expression
* @param errorMessage the exception message to use if the check fails; will
* be converted to a string using {@link String#valueOf(Object)}
* @throws IllegalStateException if {@code expression} is false
*/
public static void checkState(boolean expression, Object errorMessage) {
if (!expression) {
throw new IllegalStateException(String.valueOf(errorMessage));
}
}
/**
* Ensures the truth of an expression involving the state of the calling
* instance, but not involving any parameters to the calling method.
*
* @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 IllegalStateException if {@code expression} is false
* @throws NullPointerException if the check fails and either {@code
* errorMessageTemplate} or {@code errorMessageArgs} is null (don't let
* this happen)
*/
public static void checkState(boolean expression,
String errorMessageTemplate, Object... errorMessageArgs) {
if (!expression) {
throw new IllegalStateException(
format(errorMessageTemplate, errorMessageArgs));
}
}
/**
* Ensures that an object reference passed as a parameter to the calling
* method is not null.
*
* @param reference an object reference
* @return the non-null reference that was validated
* @throws NullPointerException if {@code reference} is null
*/
public static T checkNotNull(T reference) {
if (reference == null) {
throw new NullPointerException();
}
return reference;
}
/**
* Ensures that an object reference passed as a parameter to the calling
* method is not null.
*
* @param reference an object reference
* @param errorMessage the exception message to use if the check fails; will
* be converted to a string using {@link String#valueOf(Object)}
* @return the non-null reference that was validated
* @throws NullPointerException if {@code reference} is null
*/
public static T checkNotNull(T reference, Object errorMessage) {
if (reference == null) {
throw new NullPointerException(String.valueOf(errorMessage));
}
return reference;
}
/**
* Ensures that an object reference passed as a parameter to the calling
* method is not null.
*
* @param reference an object reference
* @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 the non-null reference that was validated
* @throws NullPointerException if {@code reference} is null
*/
public static T checkNotNull(T reference, String errorMessageTemplate,
Object... errorMessageArgs) {
if (reference == null) {
// If either of these parameters is null, the right thing happens anyway
throw new NullPointerException(
format(errorMessageTemplate, errorMessageArgs));
}
return reference;
}
/**
* Ensures that an {@code Iterable} object passed as a parameter to the
* calling method is not null and contains no null elements.
*
* @param iterable the iterable to check the contents of
* @return the non-null {@code iterable} reference just validated
* @throws NullPointerException if {@code iterable} is null or contains at
* least one null element
*/
public static > T checkContentsNotNull(T iterable) {
if (containsOrIsNull(iterable)) {
throw new NullPointerException();
}
return iterable;
}
/**
* Ensures that an {@code Iterable} object passed as a parameter to the
* calling method is not null and contains no null elements.
*
* @param iterable the iterable to check the contents of
* @param errorMessage the exception message to use if the check fails; will
* be converted to a string using {@link String#valueOf(Object)}
* @return the non-null {@code iterable} reference just validated
* @throws NullPointerException if {@code iterable} is null or contains at
* least one null element
*/
public static > T checkContentsNotNull(
T iterable, Object errorMessage) {
if (containsOrIsNull(iterable)) {
throw new NullPointerException(String.valueOf(errorMessage));
}
return iterable;
}
/**
* Ensures that an {@code Iterable} object passed as a parameter to the
* calling method is not null and contains no null elements.
*
* @param iterable the iterable to check the contents of
* @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 the non-null {@code iterable} reference just validated
* @throws NullPointerException if {@code iterable} is null or contains at
* least one null element
*/
public static > T checkContentsNotNull(T iterable,
String errorMessageTemplate, Object... errorMessageArgs) {
if (containsOrIsNull(iterable)) {
throw new NullPointerException(
format(errorMessageTemplate, errorMessageArgs));
}
return iterable;
}
private static boolean containsOrIsNull(Iterable iterable) {
if (iterable == null) {
return true;
}
if (iterable instanceof Collection) {
Collection collection = (Collection) iterable;
try {
return collection.contains(null);
} catch (NullPointerException e) {
// A NPE implies that the collection doesn't contain null.
return false;
}
} else {
for (Object element : iterable) {
if (element == null) {
return true;
}
}
return false;
}
}
/**
* Substitutes each {@code %s} in {@code template} with an argument. These
* are matched by position - the first {@code %s} gets {@code args[0]}, etc.
* If there are more arguments than placeholders, the unmatched arguments will
* be appended to the end of the formatted message in square braces.
*
* @param template a non-null string containing 0 or more {@code %s}
* placeholders.
* @param args the arguments to be substituted into the message
* template. Arguments are converted to strings using
* {@link String#valueOf(Object)}. Arguments can be null.
*/
// VisibleForTesting
static String format(String template, Object... args) {
// start substituting the arguments into the '%s' placeholders
StringBuilder builder = new StringBuilder(
template.length() + 16 * args.length);
int templateStart = 0;
int i = 0;
while (i < args.length) {
int placeholderStart = template.indexOf("%s", templateStart);
if (placeholderStart == -1) {
break;
}
builder.append(template.substring(templateStart, placeholderStart));
builder.append(args[i++]);
templateStart = placeholderStart + 2;
}
builder.append(template.substring(templateStart));
// if we run out of placeholders, append the extra args in square braces
if (i < args.length) {
builder.append(" [");
builder.append(args[i++]);
while (i < args.length) {
builder.append(", ");
builder.append(args[i++]);
}
builder.append("]");
}
return builder.toString();
}
}