com.google.common.base.Preconditions Maven / Gradle / Ivy
/*
* Copyright (C) 2007 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 com.google.common.annotations.GwtCompatible;
import javax.annotation.Nullable;
/**
* 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
* {@code boolean} expression which is expected to be {@code true} (or in the case of {@code
* checkNotNull}, an object reference which is expected to be non-null). When {@code false} (or
* {@code null}) is passed instead, the {@code Preconditions} method throws an unchecked exception,
* which helps the calling method communicate to its caller that that caller has made
* a mistake. Example: {@code
*
* /**
* * Returns the positive square root of the given value.
* *
* * @throws IllegalArgumentException if the value is negative
* *}{@code /
* 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);
* }}
*
* In this example, {@code checkArgument} throws an {@code IllegalArgumentException} to indicate
* that {@code exampleBadCaller} made an error in its call to {@code sqrt}.
*
* 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:
*
{@code
*
* 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 {@link java.util.NoSuchElementException} or {@link
* 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.
*
*
{@code java.util.Objects.requireNonNull()}
*
* Projects which use {@code com.google.common} should generally avoid the use of {@link
* java.util.Objects#requireNonNull(Object)}. Instead, use whichever of {@link
* #checkNotNull(Object)} or {@link Verify#verifyNotNull(Object)} is appropriate to the situation.
* (The same goes for the message-accepting overloads.)
*
*
Only {@code %s} is supported
*
* In {@code Preconditions} error message template strings, only the {@code "%s"} specifier is
* supported, not the full range of {@link java.util.Formatter} specifiers.
*
*
More information
*
* See the Guava User Guide on
* using {@code
* Preconditions}.
*
* @author Kevin Bourrillion
* @since 2.0 (imported from Google Collections Library)
*/
@GwtCompatible
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, @Nullable 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,
@Nullable String errorMessageTemplate,
@Nullable 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, @Nullable 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,
@Nullable String errorMessageTemplate,
@Nullable 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, @Nullable 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,
@Nullable String errorMessageTemplate,
@Nullable 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;
}
/*
* All recent hotspots (as of 2009) *really* like to have the natural code
*
* if (guardExpression) {
* throw new BadException(messageExpression);
* }
*
* refactored so that messageExpression is moved to a separate String-returning method.
*
* if (guardExpression) {
* throw new BadException(badMsg(...));
* }
*
* The alternative natural refactorings into void or Exception-returning methods are much slower.
* This is a big deal - we're talking factors of 2-8 in microbenchmarks, not just 10-20%. (This
* is a hotspot optimizer bug, which should be fixed, but that's a separate, big project).
*
* The coding pattern above is heavily used in java.util, e.g. in ArrayList. There is a
* RangeCheckMicroBenchmark in the JDK that was used to test this.
*
* But the methods in this class want to throw different exceptions, depending on the args, so it
* appears that this pattern is not directly applicable. But we can use the ridiculous, devious
* trick of throwing an exception in the middle of the construction of another exception. Hotspot
* is fine with that.
*/
/**
* Ensures that {@code index} specifies a valid element in an array, list or string of size
* {@code size}. An element index may range from zero, inclusive, to {@code size}, exclusive.
*
* @param index a user-supplied index identifying an element of an array, list or string
* @param size the size of that array, list or string
* @return the value of {@code index}
* @throws IndexOutOfBoundsException if {@code index} is negative or is not less than {@code size}
* @throws IllegalArgumentException if {@code size} is negative
*/
public static int checkElementIndex(int index, int size) {
return checkElementIndex(index, size, "index");
}
/**
* Ensures that {@code index} specifies a valid element in an array, list or string of size
* {@code size}. An element index may range from zero, inclusive, to {@code size}, exclusive.
*
* @param index a user-supplied index identifying an element of an array, list or string
* @param size the size of that array, list or string
* @param desc the text to use to describe this index in an error message
* @return the value of {@code index}
* @throws IndexOutOfBoundsException if {@code index} is negative or is not less than {@code size}
* @throws IllegalArgumentException if {@code size} is negative
*/
public static int checkElementIndex(
int index, int size, @Nullable String desc) {
// Carefully optimized for execution by hotspot (explanatory comment above)
if (index < 0 || index >= size) {
throw new IndexOutOfBoundsException(badElementIndex(index, size, desc));
}
return index;
}
private static String badElementIndex(int index, int size, String desc) {
if (index < 0) {
return format("%s (%s) must not be negative", desc, index);
} else if (size < 0) {
throw new IllegalArgumentException("negative size: " + size);
} else { // index >= size
return format("%s (%s) must be less than size (%s)", desc, index, size);
}
}
/**
* Ensures that {@code index} specifies a valid position in an array, list or string of
* size {@code size}. A position index may range from zero to {@code size}, inclusive.
*
* @param index a user-supplied index identifying a position in an array, list or string
* @param size the size of that array, list or string
* @return the value of {@code index}
* @throws IndexOutOfBoundsException if {@code index} is negative or is greater than {@code size}
* @throws IllegalArgumentException if {@code size} is negative
*/
public static int checkPositionIndex(int index, int size) {
return checkPositionIndex(index, size, "index");
}
/**
* Ensures that {@code index} specifies a valid position in an array, list or string of
* size {@code size}. A position index may range from zero to {@code size}, inclusive.
*
* @param index a user-supplied index identifying a position in an array, list or string
* @param size the size of that array, list or string
* @param desc the text to use to describe this index in an error message
* @return the value of {@code index}
* @throws IndexOutOfBoundsException if {@code index} is negative or is greater than {@code size}
* @throws IllegalArgumentException if {@code size} is negative
*/
public static int checkPositionIndex(int index, int size, @Nullable String desc) {
// Carefully optimized for execution by hotspot (explanatory comment above)
if (index < 0 || index > size) {
throw new IndexOutOfBoundsException(badPositionIndex(index, size, desc));
}
return index;
}
private static String badPositionIndex(int index, int size, String desc) {
if (index < 0) {
return format("%s (%s) must not be negative", desc, index);
} else if (size < 0) {
throw new IllegalArgumentException("negative size: " + size);
} else { // index > size
return format("%s (%s) must not be greater than size (%s)", desc, index, size);
}
}
/**
* Ensures that {@code start} and {@code end} specify a valid positions in an array, list
* or string of size {@code size}, and are in order. A position index may range from zero to
* {@code size}, inclusive.
*
* @param start a user-supplied index identifying a starting position in an array, list or string
* @param end a user-supplied index identifying a ending position in an array, list or string
* @param size the size of that array, list or string
* @throws IndexOutOfBoundsException if either index is negative or is greater than {@code size},
* or if {@code end} is less than {@code start}
* @throws IllegalArgumentException if {@code size} is negative
*/
public static void checkPositionIndexes(int start, int end, int size) {
// Carefully optimized for execution by hotspot (explanatory comment above)
if (start < 0 || end < start || end > size) {
throw new IndexOutOfBoundsException(badPositionIndexes(start, end, size));
}
}
private static String badPositionIndexes(int start, int end, int size) {
if (start < 0 || start > size) {
return badPositionIndex(start, size, "start index");
}
if (end < 0 || end > size) {
return badPositionIndex(end, size, "end index");
}
// end < start
return format("end index (%s) must not be less than start index (%s)", end, start);
}
/**
* 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.
*/
// Note that this is somewhat-improperly used from Verify.java as well.
static String format(String template, @Nullable Object... args) {
template = String.valueOf(template); // null -> "null"
// 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();
}
}