/*
* 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 static com.google.common.base.Preconditions.checkNotNull;
import com.google.common.annotations.GwtCompatible;
import java.util.Arrays;
import javax.annotation.Nullable;
/**
* Helper functions that can operate on any {@code Object}.
*
* @author Laurence Gonsalves
* @since 2.0 (imported from Google Collections Library)
*/
@GwtCompatible
public final class Objects {
private Objects() {}
/**
* Determines whether two possibly-null objects are equal. Returns:
*
* <ul>
* <li>{@code true} if {@code a} and {@code b} are both null.
* <li>{@code true} if {@code a} and {@code b} are both non-null and they are
* equal according to {@link Object#equals(Object)}.
* <li>{@code false} in all other situations.
* </ul>
*
* <p>This assumes that any non-null objects passed to this function conform
* to the {@code equals()} contract.
*/
public static boolean equal(@Nullable Object a, @Nullable Object b) {
return a == b || (a != null && a.equals(b));
}
/**
* Generates a hash code for multiple values. The hash code is generated by
* calling {@link Arrays#hashCode(Object[])}.
*
* <p>This is useful for implementing {@link Object#hashCode()}. For example,
* in an object that has three properties, {@code x}, {@code y}, and
* {@code z}, one could write:
* <pre>
* public int hashCode() {
* return Objects.hashCode(getX(), getY(), getZ());
* }</pre>
*
* <b>Warning</b>: When a single object is supplied, the returned hash code
* does not equal the hash code of that object.
*/
public static int hashCode(@Nullable Object... objects) {
return Arrays.hashCode(objects);
}
/**
* Creates an instance of {@link ToStringHelper}.
*
* <p>This is helpful for implementing {@link Object#toString()}.
* Specification by example: <pre> {@code
* // Returns "ClassName{}"
* Objects.toStringHelper(this)
* .toString();
*
* // Returns "ClassName{x=1}"
* Objects.toStringHelper(this)
* .add("x", 1)
* .toString();
*
* // Returns "MyObject{x=1}"
* Objects.toStringHelper("MyObject")
* .add("x", 1)
* .toString();
*
* // Returns "ClassName{x=1, y=foo}"
* Objects.toStringHelper(this)
* .add("x", 1)
* .add("y", "foo")
* .toString();
* }}</pre>
*
* <p>Note that in GWT, class names are often obfuscated.
*
* @param self the object to generate the string for (typically {@code this}),
* used only for its class name
* @since 2.0
*/
public static ToStringHelper toStringHelper(Object self) {
return new ToStringHelper(simpleName(self.getClass()));
}
/**
* Creates an instance of {@link ToStringHelper} in the same manner as
* {@link Objects#toStringHelper(Object)}, but using the name of {@code clazz}
* instead of using an instance's {@link Object#getClass()}.
*
* <p>Note that in GWT, class names are often obfuscated.
*
* @param clazz the {@link Class} of the instance
* @since 7.0 (source-compatible since 2.0)
*/
public static ToStringHelper toStringHelper(Class<?> clazz) {
return new ToStringHelper(simpleName(clazz));
}
/**
* Creates an instance of {@link ToStringHelper} in the same manner as
* {@link Objects#toStringHelper(Object)}, but using {@code className} instead
* of using an instance's {@link Object#getClass()}.
*
* @param className the name of the instance type
* @since 7.0 (source-compatible since 2.0)
*/
public static ToStringHelper toStringHelper(String className) {
return new ToStringHelper(className);
}
/**
* {@link Class#getSimpleName()} is not GWT compatible yet, so we
* provide our own implementation.
*/
private static String simpleName(Class<?> clazz) {
String name = clazz.getName();
// the nth anonymous class has a class name ending in "Outer$n"
// and local inner classes have names ending in "Outer.$1Inner"
name = name.replaceAll("\\$[0-9]+", "\\$");
// we want the name of the inner class all by its lonesome
int start = name.lastIndexOf('$');
// if this isn't an inner class, just find the start of the
// top level class name.
if (start == -1) {
start = name.lastIndexOf('.');
}
return name.substring(start + 1);
}
/**
* Returns the first of two given parameters that is not {@code null}, if
* either is, or otherwise throws a {@link NullPointerException}.
*
* <p><b>Note:</b> if {@code first} is represented as an {@code Optional<T>},
* this can be accomplished with {@code first.or(second)}. That approach also
* allows for lazy evaluation of the fallback instance, using
* {@code first.or(Supplier)}.
*
* @return {@code first} if {@code first} is not {@code null}, or
* {@code second} if {@code first} is {@code null} and {@code second} is
* not {@code null}
* @throws NullPointerException if both {@code first} and {@code second} were
* {@code null}
* @since 3.0
*/
public static <T> T firstNonNull(@Nullable T first, @Nullable T second) {
return first != null ? first : checkNotNull(second);
}
/**
* Support class for {@link Objects#toStringHelper}.
*
* @author Jason Lee
* @since 2.0
*/
public static final class ToStringHelper {
private final StringBuilder builder;
private boolean needsSeparator = false;
/**
* Use {@link Objects#toStringHelper(Object)} to create an instance.
*/
private ToStringHelper(String className) {
checkNotNull(className);
this.builder = new StringBuilder(32).append(className).append('{');
}
/**
* Adds a name/value pair to the formatted output in {@code name=value}
* format. If {@code value} is {@code null}, the string {@code "null"}
* is used.
*/
public ToStringHelper add(String name, @Nullable Object value) {
checkNotNull(name);
maybeAppendSeparator().append(name).append('=').append(value);
return this;
}
/**
* Adds a value to the formatted output in {@code value} format.
*
* <p>It is strongly encouraged to use {@link #add(String, Object)} instead
* and give value a readable name.
*/
public ToStringHelper addValue(@Nullable Object value) {
maybeAppendSeparator().append(value);
return this;
}
/**
* Returns a string in the format specified by {@link
* Objects#toStringHelper(Object)}.
*/
@Override public String toString() {
try {
return builder.append('}').toString();
} finally {
// Slice off the closing brace in case there are additional calls to
// #add or #addValue.
builder.setLength(builder.length() - 1);
}
}
private StringBuilder maybeAppendSeparator() {
if (needsSeparator) {
return builder.append(", ");
} else {
needsSeparator = true;
return builder;
}
}
}
}
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