506 lines
20 KiB
Java
506 lines
20 KiB
Java
/*
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* Copyright (C) 2007 The Guava Authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
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* in compliance with the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software distributed under the License
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* is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
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* or implied. See the License for the specific language governing permissions and limitations under
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* the License.
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*/
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package com.google.common.base;
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import javax.annotation.Nullable;
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import com.google.common.annotations.GwtCompatible;
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/**
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* Static convenience methods that help a method or constructor check whether it
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* was invoked correctly (whether its <i>preconditions</i> have been met). These
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* methods generally accept a {@code boolean} expression which is expected to be
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* {@code true} (or in the case of {@code
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* checkNotNull}, an object reference which is expected to be non-null). When
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* {@code false} (or {@code null}) is passed instead, the {@code Preconditions}
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* method throws an unchecked exception, which helps the calling method
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* communicate to <i>its</i> caller that <i>that</i> caller has made a mistake.
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* Example:
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*
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* <pre>
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* {@code
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*
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* /**
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* * Returns the positive square root of the given value.
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* *
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* * @throws IllegalArgumentException if the value is negative
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* *}{@code /
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* public static double sqrt(double value) {
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* Preconditions.checkArgument(value >= 0.0, "negative value: %s", value);
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* // calculate the square root
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* }
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*
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* void exampleBadCaller() {
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* double d = sqrt(-1.0);
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* }}
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* </pre>
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*
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* In this example, {@code checkArgument} throws an
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* {@code IllegalArgumentException} to indicate that {@code exampleBadCaller}
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* made an error in <i>its</i> call to {@code sqrt}.
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*
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* <h3>Warning about performance</h3>
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*
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* <p>
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* The goal of this class is to improve readability of code, but in some
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* circumstances this may come at a significant performance cost. Remember that
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* parameter values for message construction must all be computed eagerly, and
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* autoboxing and varargs array creation may happen as well, even when the
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* precondition check then succeeds (as it should almost always do in
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* production). In some circumstances these wasted CPU cycles and allocations
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* can add up to a real problem. Performance-sensitive precondition checks can
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* always be converted to the customary form:
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*
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* <pre>
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* {@code
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*
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* if (value < 0.0) {
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* throw new IllegalArgumentException("negative value: " + value);
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* }}
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* </pre>
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*
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* <h3>Other types of preconditions</h3>
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*
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* <p>
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* Not every type of precondition failure is supported by these methods.
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* Continue to throw standard JDK exceptions such as
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* {@link java.util.NoSuchElementException} or
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* {@link UnsupportedOperationException} in the situations they are intended
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* for.
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*
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* <h3>Non-preconditions</h3>
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*
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* <p>
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* It is of course possible to use the methods of this class to check for
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* invalid conditions which are <i>not the caller's fault</i>. Doing so is
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* <b>not recommended</b> because it is misleading to future readers of the code
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* and of stack traces. See <a href=
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* "http://code.google.com/p/guava-libraries/wiki/ConditionalFailuresExplained">Conditional
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* failures explained</a> in the Guava User Guide for more advice.
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*
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* <h3>{@code java.util.Objects.requireNonNull()}</h3>
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*
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* <p>
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* Projects which use {@code com.google.common} should generally avoid the use
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* of {@link java.util.Objects#requireNonNull(Object)}. Instead, use whichever
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* of {@link #checkNotNull(Object)} or {@link Verify#verifyNotNull(Object)} is
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* appropriate to the situation. (The same goes for the message-accepting
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* overloads.)
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*
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* <h3>Only {@code %s} is supported</h3>
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*
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* <p>
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* In {@code Preconditions} error message template strings, only the
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* {@code "%s"} specifier is supported, not the full range of
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* {@link java.util.Formatter} specifiers. However, note that if the number of
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* arguments does not match the number of occurrences of {@code "%s"} in the
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* format string, {@code Preconditions} will still behave as expected, and will
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* still include all argument values in the error message; the message will
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* simply not be formatted exactly as intended.
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*
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* <h3>More information</h3>
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*
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* <p>
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* See the Guava User Guide on <a href=
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* "http://code.google.com/p/guava-libraries/wiki/PreconditionsExplained">using
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* {@code
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* Preconditions}</a>.
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*
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* @author Kevin Bourrillion
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* @since 2.0 (imported from Google Collections Library)
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*/
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@GwtCompatible
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public final class Preconditions {
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private Preconditions() {
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}
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/**
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* Ensures the truth of an expression involving one or more parameters to the
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* calling method.
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*
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* @param expression a boolean expression
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* @throws IllegalArgumentException if {@code expression} is false
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*/
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public static void checkArgument(boolean expression) {
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if (!expression) {
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throw new IllegalArgumentException();
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}
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}
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/**
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* Ensures the truth of an expression involving one or more parameters to the
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* calling method.
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*
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* @param expression a boolean expression
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* @param errorMessage the exception message to use if the check fails; will be
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* converted to a string using
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* {@link String#valueOf(Object)}
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* @throws IllegalArgumentException if {@code expression} is false
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*/
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public static void checkArgument(boolean expression, @Nullable Object errorMessage) {
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if (!expression) {
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throw new IllegalArgumentException(String.valueOf(errorMessage));
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}
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}
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/**
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* Ensures the truth of an expression involving one or more parameters to the
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* calling method.
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*
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* @param expression a boolean expression
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* @param errorMessageTemplate a template for the exception message should the
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* check fail. The message is formed by replacing
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* each {@code %s} placeholder in the template with
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* an argument. These are matched by position - the
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* first {@code %s} gets {@code
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* errorMessageArgs[0]} , etc. Unmatched arguments will be appended to
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* the formatted message in square braces. Unmatched
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* placeholders will be left as-is.
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* @param errorMessageArgs the arguments to be substituted into the message
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* template. Arguments are converted to strings
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* using {@link String#valueOf(Object)}.
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* @throws IllegalArgumentException if {@code expression} is false
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* @throws NullPointerException if the check fails and either
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* {@code errorMessageTemplate} or
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* {@code errorMessageArgs} is null (don't let
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* this happen)
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*/
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public static void checkArgument(boolean expression, @Nullable String errorMessageTemplate,
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@Nullable Object... errorMessageArgs) {
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if (!expression) {
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throw new IllegalArgumentException(format(errorMessageTemplate, errorMessageArgs));
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}
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}
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/**
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* Ensures the truth of an expression involving the state of the calling
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* instance, but not involving any parameters to the calling method.
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*
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* @param expression a boolean expression
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* @throws IllegalStateException if {@code expression} is false
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*/
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public static void checkState(boolean expression) {
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if (!expression) {
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throw new IllegalStateException();
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}
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}
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/**
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* Ensures the truth of an expression involving the state of the calling
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* instance, but not involving any parameters to the calling method.
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*
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* @param expression a boolean expression
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* @param errorMessage the exception message to use if the check fails; will be
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* converted to a string using
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* {@link String#valueOf(Object)}
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* @throws IllegalStateException if {@code expression} is false
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*/
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public static void checkState(boolean expression, @Nullable Object errorMessage) {
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if (!expression) {
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throw new IllegalStateException(String.valueOf(errorMessage));
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}
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}
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/**
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* Ensures the truth of an expression involving the state of the calling
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* instance, but not involving any parameters to the calling method.
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*
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* @param expression a boolean expression
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* @param errorMessageTemplate a template for the exception message should the
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* check fail. The message is formed by replacing
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* each {@code %s} placeholder in the template with
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* an argument. These are matched by position - the
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* first {@code %s} gets {@code
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* errorMessageArgs[0]} , etc. Unmatched arguments will be appended to
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* the formatted message in square braces. Unmatched
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* placeholders will be left as-is.
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* @param errorMessageArgs the arguments to be substituted into the message
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* template. Arguments are converted to strings
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* using {@link String#valueOf(Object)}.
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* @throws IllegalStateException if {@code expression} is false
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* @throws NullPointerException if the check fails and either
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* {@code errorMessageTemplate} or
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* {@code errorMessageArgs} is null (don't let
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* this happen)
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*/
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public static void checkState(boolean expression, @Nullable String errorMessageTemplate,
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@Nullable Object... errorMessageArgs) {
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if (!expression) {
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throw new IllegalStateException(format(errorMessageTemplate, errorMessageArgs));
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}
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}
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/**
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* Ensures that an object reference passed as a parameter to the calling method
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* is not null.
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*
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* @param reference an object reference
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* @return the non-null reference that was validated
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* @throws NullPointerException if {@code reference} is null
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*/
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public static <T> T checkNotNull(T reference) {
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if (reference == null) {
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throw new NullPointerException();
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}
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return reference;
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}
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/**
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* Ensures that an object reference passed as a parameter to the calling method
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* is not null.
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*
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* @param reference an object reference
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* @param errorMessage the exception message to use if the check fails; will be
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* converted to a string using
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* {@link String#valueOf(Object)}
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* @return the non-null reference that was validated
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* @throws NullPointerException if {@code reference} is null
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*/
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public static <T> T checkNotNull(T reference, @Nullable Object errorMessage) {
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if (reference == null) {
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throw new NullPointerException(String.valueOf(errorMessage));
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}
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return reference;
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}
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/**
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* Ensures that an object reference passed as a parameter to the calling method
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* is not null.
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*
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* @param reference an object reference
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* @param errorMessageTemplate a template for the exception message should the
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* check fail. The message is formed by replacing
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* each {@code %s} placeholder in the template with
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* an argument. These are matched by position - the
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* first {@code %s} gets {@code
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* errorMessageArgs[0]} , etc. Unmatched arguments will be appended to
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* the formatted message in square braces. Unmatched
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* placeholders will be left as-is.
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* @param errorMessageArgs the arguments to be substituted into the message
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* template. Arguments are converted to strings
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* using {@link String#valueOf(Object)}.
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* @return the non-null reference that was validated
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* @throws NullPointerException if {@code reference} is null
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*/
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public static <T> T checkNotNull(T reference, @Nullable String errorMessageTemplate,
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@Nullable Object... errorMessageArgs) {
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if (reference == null) {
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// If either of these parameters is null, the right thing happens anyway
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throw new NullPointerException(format(errorMessageTemplate, errorMessageArgs));
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}
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return reference;
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}
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/*
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* All recent hotspots (as of 2009) *really* like to have the natural code
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*
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* if (guardExpression) { throw new BadException(messageExpression); }
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*
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* refactored so that messageExpression is moved to a separate String-returning
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* method.
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*
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* if (guardExpression) { throw new BadException(badMsg(...)); }
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*
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* The alternative natural refactorings into void or Exception-returning methods
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* are much slower. This is a big deal - we're talking factors of 2-8 in
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* microbenchmarks, not just 10-20%. (This is a hotspot optimizer bug, which
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* should be fixed, but that's a separate, big project).
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*
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* The coding pattern above is heavily used in java.util, e.g. in ArrayList.
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* There is a RangeCheckMicroBenchmark in the JDK that was used to test this.
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*
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* But the methods in this class want to throw different exceptions, depending
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* on the args, so it appears that this pattern is not directly applicable. But
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* we can use the ridiculous, devious trick of throwing an exception in the
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* middle of the construction of another exception. Hotspot is fine with that.
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*/
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/**
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* Ensures that {@code index} specifies a valid <i>element</i> in an array, list
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* or string of size {@code size}. An element index may range from zero,
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* inclusive, to {@code size}, exclusive.
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*
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* @param index a user-supplied index identifying an element of an array, list
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* or string
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* @param size the size of that array, list or string
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* @return the value of {@code index}
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* @throws IndexOutOfBoundsException if {@code index} is negative or is not less
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* than {@code size}
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* @throws IllegalArgumentException if {@code size} is negative
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*/
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public static int checkElementIndex(int index, int size) {
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return checkElementIndex(index, size, "index");
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}
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/**
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* Ensures that {@code index} specifies a valid <i>element</i> in an array, list
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* or string of size {@code size}. An element index may range from zero,
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* inclusive, to {@code size}, exclusive.
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*
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* @param index a user-supplied index identifying an element of an array, list
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* or string
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* @param size the size of that array, list or string
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* @param desc the text to use to describe this index in an error message
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* @return the value of {@code index}
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* @throws IndexOutOfBoundsException if {@code index} is negative or is not less
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* than {@code size}
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* @throws IllegalArgumentException if {@code size} is negative
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*/
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public static int checkElementIndex(int index, int size, @Nullable String desc) {
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// Carefully optimized for execution by hotspot (explanatory comment above)
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if (index < 0 || index >= size) {
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throw new IndexOutOfBoundsException(badElementIndex(index, size, desc));
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}
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return index;
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}
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private static String badElementIndex(int index, int size, String desc) {
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if (index < 0) {
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return format("%s (%s) must not be negative", desc, index);
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} else if (size < 0) {
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throw new IllegalArgumentException("negative size: " + size);
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} else { // index >= size
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return format("%s (%s) must be less than size (%s)", desc, index, size);
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}
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}
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/**
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* Ensures that {@code index} specifies a valid <i>position</i> in an array,
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* list or string of size {@code size}. A position index may range from zero to
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* {@code size}, inclusive.
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*
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* @param index a user-supplied index identifying a position in an array, list
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* or string
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* @param size the size of that array, list or string
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* @return the value of {@code index}
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* @throws IndexOutOfBoundsException if {@code index} is negative or is greater
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* than {@code size}
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* @throws IllegalArgumentException if {@code size} is negative
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*/
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public static int checkPositionIndex(int index, int size) {
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return checkPositionIndex(index, size, "index");
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}
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/**
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* Ensures that {@code index} specifies a valid <i>position</i> in an array,
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* list or string of size {@code size}. A position index may range from zero to
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* {@code size}, inclusive.
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*
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* @param index a user-supplied index identifying a position in an array, list
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* or string
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* @param size the size of that array, list or string
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* @param desc the text to use to describe this index in an error message
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* @return the value of {@code index}
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* @throws IndexOutOfBoundsException if {@code index} is negative or is greater
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* than {@code size}
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* @throws IllegalArgumentException if {@code size} is negative
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*/
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public static int checkPositionIndex(int index, int size, @Nullable String desc) {
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// Carefully optimized for execution by hotspot (explanatory comment above)
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if (index < 0 || index > size) {
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throw new IndexOutOfBoundsException(badPositionIndex(index, size, desc));
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}
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return index;
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}
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private static String badPositionIndex(int index, int size, String desc) {
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if (index < 0) {
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return format("%s (%s) must not be negative", desc, index);
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} else if (size < 0) {
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throw new IllegalArgumentException("negative size: " + size);
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} else { // index > size
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return format("%s (%s) must not be greater than size (%s)", desc, index, size);
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}
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}
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/**
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* Ensures that {@code start} and {@code end} specify a valid <i>positions</i>
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* in an array, list or string of size {@code size}, and are in order. A
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* position index may range from zero to {@code size}, inclusive.
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*
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* @param start a user-supplied index identifying a starting position in an
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* array, list or string
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* @param end a user-supplied index identifying a ending position in an array,
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* list or string
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* @param size the size of that array, list or string
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* @throws IndexOutOfBoundsException if either index is negative or is greater
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* than {@code size}, or if {@code end} is
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* less than {@code start}
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* @throws IllegalArgumentException if {@code size} is negative
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*/
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public static void checkPositionIndexes(int start, int end, int size) {
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// Carefully optimized for execution by hotspot (explanatory comment above)
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if (start < 0 || end < start || end > size) {
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throw new IndexOutOfBoundsException(badPositionIndexes(start, end, size));
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}
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}
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private static String badPositionIndexes(int start, int end, int size) {
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if (start < 0 || start > size) {
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return badPositionIndex(start, size, "start index");
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}
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if (end < 0 || end > size) {
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return badPositionIndex(end, size, "end index");
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}
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// end < start
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return format("end index (%s) must not be less than start index (%s)", end, start);
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}
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/**
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* Substitutes each {@code %s} in {@code template} with an argument. These are
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* matched by position: the first {@code %s} gets {@code args[0]}, etc. If there
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* are more arguments than placeholders, the unmatched arguments will be
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* appended to the end of the formatted message in square braces.
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*
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* @param template a non-null string containing 0 or more {@code %s}
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* placeholders.
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* @param args the arguments to be substituted into the message template.
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* Arguments are converted to strings using
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* {@link String#valueOf(Object)}. Arguments can be null.
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*/
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// Note that this is somewhat-improperly used from Verify.java as well.
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static String format(String template, @Nullable Object... args) {
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template = String.valueOf(template); // null -> "null"
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// start substituting the arguments into the '%s' placeholders
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StringBuilder builder = new StringBuilder(template.length() + 16 * args.length);
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int templateStart = 0;
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int i = 0;
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while (i < args.length) {
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int placeholderStart = template.indexOf("%s", templateStart);
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if (placeholderStart == -1) {
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break;
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}
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builder.append(template.substring(templateStart, placeholderStart));
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builder.append(args[i++]);
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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();
|
|
}
|
|
}
|