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/*
* 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 com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.Arrays;
import javax.annotation.Nullable;
/**
* Helper functions that can operate on any {@code Object}.
*
* See the Guava User Guide on
* writing
* {@code Object} methods with {@code Objects}.
*
* @author Laurence Gonsalves
* @since 2.0
*/
@GwtCompatible
public final class Objects extends ExtraObjectsMethodsForWeb {
private Objects() {}
/**
* Determines whether two possibly-null objects are equal. Returns:
*
*
* - {@code true} if {@code a} and {@code b} are both null.
*
- {@code true} if {@code a} and {@code b} are both non-null and they are equal according to
* {@link Object#equals(Object)}.
*
- {@code false} in all other situations.
*
*
* This assumes that any non-null objects passed to this function conform to the
* {@code equals()} contract.
*
*
Note for Java 7 and later: This method should be treated as deprecated; use
* {@link java.util.Objects#equals} instead.
*/
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[])}. 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.
*
*
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:
*
*
{@code
* public int hashCode() {
* return Objects.hashCode(getX(), getY(), getZ());
* }}
*
* Warning: When a single object is supplied, the returned hash code does not equal the
* hash code of that object.
*
*
Note for Java 7 and later: This method should be treated as deprecated; use
* {@link java.util.Objects#hash} instead.
*/
public static int hashCode(@Nullable Object... objects) {
return Arrays.hashCode(objects);
}
/**
* Creates an instance of {@link ToStringHelper}.
*
*
This is helpful for implementing {@link Object#toString()}. Specification by example:
*
*
{@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();
* }}
*
* 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
* @deprecated Use {@link MoreObjects#toStringHelper(Object)} instead. This method is scheduled
* for removal in Guava 21.0.
*/
@Deprecated
public static ToStringHelper toStringHelper(Object self) {
return new ToStringHelper(self.getClass().getSimpleName());
}
/**
* 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()}.
*
*
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)
* @deprecated Use {@link MoreObjects#toStringHelper(Class)} instead. This method is scheduled for
* removal in Guava 21.0.
*/
@Deprecated
public static ToStringHelper toStringHelper(Class clazz) {
return new ToStringHelper(clazz.getSimpleName());
}
/**
* 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)
* @deprecated Use {@link MoreObjects#toStringHelper(String)} instead. This method is scheduled
* for removal in Guava 21.0.
*/
@Deprecated
public static ToStringHelper toStringHelper(String className) {
return new ToStringHelper(className);
}
/**
* Returns the first of two given parameters that is not {@code null}, if either is, or otherwise
* throws a {@link NullPointerException}.
*
*
Note: 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
* @deprecated Use {@link MoreObjects#firstNonNull} instead. This method is scheduled for removal
* in Guava 21.0.
*/
@Deprecated
public static T firstNonNull(@Nullable T first, @Nullable T second) {
return MoreObjects.firstNonNull(first, second);
}
/**
* Support class for {@link Objects#toStringHelper}.
*
* @author Jason Lee
* @since 2.0
* @deprecated Use {@link MoreObjects.ToStringHelper} instead. This class is scheduled for removal
* in Guava 21.0.
*/
@Deprecated
public static final class ToStringHelper {
private final String className;
private final 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
*/
@CanIgnoreReturnValue
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.
*/
@CanIgnoreReturnValue
public ToStringHelper add(String name, @Nullable 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)
*/
@CanIgnoreReturnValue
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)
*/
@CanIgnoreReturnValue
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)
*/
@CanIgnoreReturnValue
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)
*/
@CanIgnoreReturnValue
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)
*/
@CanIgnoreReturnValue
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)
*/
@CanIgnoreReturnValue
public ToStringHelper add(String name, long value) {
return addHolder(name, String.valueOf(value));
}
/**
* Adds an unnamed value to the formatted output.
*
* It is strongly encouraged to use {@link #add(String, Object)} instead and give value a
* readable name.
*/
@CanIgnoreReturnValue
public ToStringHelper addValue(@Nullable Object value) {
return addHolder(value);
}
/**
* Adds an unnamed value to the formatted output.
*
*
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)
*/
@CanIgnoreReturnValue
public ToStringHelper addValue(boolean value) {
return addHolder(String.valueOf(value));
}
/**
* Adds an unnamed value to the formatted output.
*
*
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)
*/
@CanIgnoreReturnValue
public ToStringHelper addValue(char value) {
return addHolder(String.valueOf(value));
}
/**
* Adds an unnamed value to the formatted output.
*
*
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)
*/
@CanIgnoreReturnValue
public ToStringHelper addValue(double value) {
return addHolder(String.valueOf(value));
}
/**
* Adds an unnamed value to the formatted output.
*
*
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)
*/
@CanIgnoreReturnValue
public ToStringHelper addValue(float value) {
return addHolder(String.valueOf(value));
}
/**
* Adds an unnamed value to the formatted output.
*
*
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)
*/
@CanIgnoreReturnValue
public ToStringHelper addValue(int value) {
return addHolder(String.valueOf(value));
}
/**
* Adds an unnamed value to the formatted output.
*
*
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)
*/
@CanIgnoreReturnValue
public ToStringHelper addValue(long value) {
return addHolder(String.valueOf(value));
}
/**
* Returns a string in the format specified by {@link Objects#toStringHelper(Object)}.
*
*
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(@Nullable Object value) {
ValueHolder valueHolder = addHolder();
valueHolder.value = value;
return this;
}
private ToStringHelper addHolder(String name, @Nullable 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;
}
}
}