/*
* 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 java.util.Arrays;
/**
* Helper functions that can operate on any {@code Object}.
*
* <p>See the Guava User Guide on <a
* href="http://code.google.com/p/guava-libraries/wiki/CommonObjectUtilitiesExplained">writing
* {@code Object} methods with {@code Objects}</a>.
*
* @author Laurence Gonsalves
* @since 2.0 (imported from Google Collections Library)
*/
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.
*
* <p><b>Note for Java 7 and later:</b> This method should be treated as
* deprecated; use {@link java.util.Objects#equals} instead.
*/
public static boolean equal(Object a, 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[])}. Note that array arguments to
* this method, with the exception of a single Object array, do not get any
* special handling; their hash codes are based on identity and not contents.
*
* <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> {@code
* public int hashCode() {
* return Objects.hashCode(getX(), getY(), getZ());
* }}</pre>
*
* <p><b>Warning:</b> When a single object is supplied, the returned hash code
* does not equal the hash code of that object.
*
* <p><b>Note for Java 7 and later:</b> This method should be treated as
* deprecated; use {@link java.util.Objects#hash} instead.
*/
public static int hashCode(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();
*
* // Returns "ClassName{x=1}"
* Objects.toStringHelper(this)
* .omitNullValues()
* .add("x", 1)
* .add("y", null)
* .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 {@link Optional},
* this can be accomplished with
* {@linkplain Optional#or(Object) first.or(second)}.
* That approach also allows for lazy evaluation of the fallback instance,
* using {@linkplain Optional#or(Supplier) 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(T first, 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 String className;
private ValueHolder holderHead = new ValueHolder();
private ValueHolder holderTail = holderHead;
private boolean omitNullValues = false;
/**
* Use {@link Objects#toStringHelper(Object)} to create an instance.
*/
private ToStringHelper(String className) {
this.className = checkNotNull(className);
}
/**
* Configures the {@link ToStringHelper} so {@link #toString()} will ignore
* properties with null value. The order of calling this method, relative
* to the {@code add()}/{@code addValue()} methods, is not significant.
*
* @since 12.0
*/
public ToStringHelper omitNullValues() {
omitNullValues = true;
return this;
}
/**
* 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, unless {@link #omitNullValues()} is called, in which case this
* name/value pair will not be added.
*/
public ToStringHelper add(String name, Object value) {
return addHolder(name, value);
}
/**
* Adds a name/value pair to the formatted output in {@code name=value}
* format.
*
* @since 11.0 (source-compatible since 2.0)
*/
public ToStringHelper add(String name, boolean value) {
return addHolder(name, String.valueOf(value));
}
/**
* Adds a name/value pair to the formatted output in {@code name=value}
* format.
*
* @since 11.0 (source-compatible since 2.0)
*/
public ToStringHelper add(String name, char value) {
return addHolder(name, String.valueOf(value));
}
/**
* Adds a name/value pair to the formatted output in {@code name=value}
* format.
*
* @since 11.0 (source-compatible since 2.0)
*/
public ToStringHelper add(String name, double value) {
return addHolder(name, String.valueOf(value));
}
/**
* Adds a name/value pair to the formatted output in {@code name=value}
* format.
*
* @since 11.0 (source-compatible since 2.0)
*/
public ToStringHelper add(String name, float value) {
return addHolder(name, String.valueOf(value));
}
/**
* Adds a name/value pair to the formatted output in {@code name=value}
* format.
*
* @since 11.0 (source-compatible since 2.0)
*/
public ToStringHelper add(String name, int value) {
return addHolder(name, String.valueOf(value));
}
/**
* Adds a name/value pair to the formatted output in {@code name=value}
* format.
*
* @since 11.0 (source-compatible since 2.0)
*/
public ToStringHelper add(String name, long value) {
return addHolder(name, String.valueOf(value));
}
/**
* Adds an unnamed value to the formatted output.
*
* <p>It is strongly encouraged to use {@link #add(String, Object)} instead
* and give value a readable name.
*/
public ToStringHelper addValue(Object value) {
return addHolder(value);
}
/**
* Adds an unnamed value to the formatted output.
*
* <p>It is strongly encouraged to use {@link #add(String, boolean)} instead
* and give value a readable name.
*
* @since 11.0 (source-compatible since 2.0)
*/
public ToStringHelper addValue(boolean value) {
return addHolder(String.valueOf(value));
}
/**
* Adds an unnamed value to the formatted output.
*
* <p>It is strongly encouraged to use {@link #add(String, char)} instead
* and give value a readable name.
*
* @since 11.0 (source-compatible since 2.0)
*/
public ToStringHelper addValue(char value) {
return addHolder(String.valueOf(value));
}
/**
* Adds an unnamed value to the formatted output.
*
* <p>It is strongly encouraged to use {@link #add(String, double)} instead
* and give value a readable name.
*
* @since 11.0 (source-compatible since 2.0)
*/
public ToStringHelper addValue(double value) {
return addHolder(String.valueOf(value));
}
/**
* Adds an unnamed value to the formatted output.
*
* <p>It is strongly encouraged to use {@link #add(String, float)} instead
* and give value a readable name.
*
* @since 11.0 (source-compatible since 2.0)
*/
public ToStringHelper addValue(float value) {
return addHolder(String.valueOf(value));
}
/**
* Adds an unnamed value to the formatted output.
*
* <p>It is strongly encouraged to use {@link #add(String, int)} instead
* and give value a readable name.
*
* @since 11.0 (source-compatible since 2.0)
*/
public ToStringHelper addValue(int value) {
return addHolder(String.valueOf(value));
}
/**
* Adds an unnamed value to the formatted output.
*
* <p>It is strongly encouraged to use {@link #add(String, long)} instead
* and give value a readable name.
*
* @since 11.0 (source-compatible since 2.0)
*/
public ToStringHelper addValue(long value) {
return addHolder(String.valueOf(value));
}
/**
* Returns a string in the format specified by {@link
* Objects#toStringHelper(Object)}.
*
* <p>After calling this method, you can keep adding more properties to later
* call toString() again and get a more complete representation of the
* same object; but properties cannot be removed, so this only allows
* limited reuse of the helper instance. The helper allows duplication of
* properties (multiple name/value pairs with the same name can be added).
*/
@Override public String toString() {
// create a copy to keep it consistent in case value changes
boolean omitNullValuesSnapshot = omitNullValues;
String nextSeparator = "";
StringBuilder builder = new StringBuilder(32).append(className)
.append('{');
for (ValueHolder valueHolder = holderHead.next; valueHolder != null;
valueHolder = valueHolder.next) {
if (!omitNullValuesSnapshot || valueHolder.value != null) {
builder.append(nextSeparator);
nextSeparator = ", ";
if (valueHolder.name != null) {
builder.append(valueHolder.name).append('=');
}
builder.append(valueHolder.value);
}
}
return builder.append('}').toString();
}
private ValueHolder addHolder() {
ValueHolder valueHolder = new ValueHolder();
holderTail = holderTail.next = valueHolder;
return valueHolder;
}
private ToStringHelper addHolder(Object value) {
ValueHolder valueHolder = addHolder();
valueHolder.value = value;
return this;
}
private ToStringHelper addHolder(String name, Object value) {
ValueHolder valueHolder = addHolder();
valueHolder.value = value;
valueHolder.name = checkNotNull(name);
return this;
}
private static final class ValueHolder {
String name;
Object value;
ValueHolder next;
}
}
public static <T> T checkNotNull(T reference) {
if (reference == null) {
throw new NullPointerException();
}
return reference;
}
}