java.com.google.common.base.MoreObjects Maven / Gradle / Ivy
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/*
* Copyright (C) 2014 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 org.checkerframework.checker.nullness.qual.Nullable;
/**
* Helper functions that operate on any {@code Object}, and are not already provided in {@link
* java.util.Objects}.
*
* See the Guava User Guide on writing {@code Object}
* methods with {@code MoreObjects}.
*
* @author Laurence Gonsalves
* @since 18.0 (since 2.0 as {@code Objects})
*/
@GwtCompatible
public final class MoreObjects {
/**
* Returns the first of two given parameters that is not {@code null}, if either is, or otherwise
* throws a {@link NullPointerException}.
*
*
To find the first non-null element in an iterable, use {@code Iterables.find(iterable,
* Predicates.notNull())}. For varargs, use {@code Iterables.find(Arrays.asList(a, b, c, ...),
* Predicates.notNull())}, static importing as necessary.
*
*
Note: if {@code first} is represented as an {@link Optional}, this can be
* accomplished with {@link Optional#or(Object) first.or(second)}. That approach also allows for
* lazy evaluation of the fallback instance, using {@link Optional#or(Supplier)
* first.or(supplier)}.
*
* @return {@code first} if it is non-null; otherwise {@code second} if it is non-null
* @throws NullPointerException if both {@code first} and {@code second} are null
* @since 18.0 (since 3.0 as {@code Objects.firstNonNull()}).
*/
public static T firstNonNull(@Nullable T first, @Nullable T second) {
if (first != null) {
return first;
}
if (second != null) {
return second;
}
throw new NullPointerException("Both parameters are null");
}
/**
* Creates an instance of {@link ToStringHelper}.
*
* This is helpful for implementing {@link Object#toString()}. Specification by example:
*
*
{@code
* // Returns "ClassName{}"
* MoreObjects.toStringHelper(this)
* .toString();
*
* // Returns "ClassName{x=1}"
* MoreObjects.toStringHelper(this)
* .add("x", 1)
* .toString();
*
* // Returns "MyObject{x=1}"
* MoreObjects.toStringHelper("MyObject")
* .add("x", 1)
* .toString();
*
* // Returns "ClassName{x=1, y=foo}"
* MoreObjects.toStringHelper(this)
* .add("x", 1)
* .add("y", "foo")
* .toString();
*
* // Returns "ClassName{x=1}"
* MoreObjects.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 18.0 (since 2.0 as {@code Objects.toStringHelper()}).
*/
public static ToStringHelper toStringHelper(Object self) {
return new ToStringHelper(self.getClass().getSimpleName());
}
/**
* Creates an instance of {@link ToStringHelper} in the same manner as {@link
* #toStringHelper(Object)}, but using the simple 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 18.0 (since 7.0 as {@code Objects.toStringHelper()}).
*/
public static ToStringHelper toStringHelper(Class clazz) {
return new ToStringHelper(clazz.getSimpleName());
}
/**
* Creates an instance of {@link ToStringHelper} in the same manner as {@link
* #toStringHelper(Object)}, but using {@code className} instead of using an instance's {@link
* Object#getClass()}.
*
* @param className the name of the instance type
* @since 18.0 (since 7.0 as {@code Objects.toStringHelper()}).
*/
public static ToStringHelper toStringHelper(String className) {
return new ToStringHelper(className);
}
/**
* Support class for {@link MoreObjects#toStringHelper}.
*
* @author Jason Lee
* @since 18.0 (since 2.0 as {@code Objects.ToStringHelper}).
*/
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 MoreObjects#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 18.0 (since 12.0 as {@code Objects.ToStringHelper.omitNullValues()}).
*/
@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 18.0 (since 11.0 as {@code Objects.ToStringHelper.add()}).
*/
@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 18.0 (since 11.0 as {@code Objects.ToStringHelper.add()}).
*/
@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 18.0 (since 11.0 as {@code Objects.ToStringHelper.add()}).
*/
@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 18.0 (since 11.0 as {@code Objects.ToStringHelper.add()}).
*/
@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 18.0 (since 11.0 as {@code Objects.ToStringHelper.add()}).
*/
@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 18.0 (since 11.0 as {@code Objects.ToStringHelper.add()}).
*/
@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 18.0 (since 11.0 as {@code Objects.ToStringHelper.addValue()}).
*/
@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 18.0 (since 11.0 as {@code Objects.ToStringHelper.addValue()}).
*/
@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 18.0 (since 11.0 as {@code Objects.ToStringHelper.addValue()}).
*/
@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 18.0 (since 11.0 as {@code Objects.ToStringHelper.addValue()}).
*/
@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 18.0 (since 11.0 as {@code Objects.ToStringHelper.addValue()}).
*/
@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 18.0 (since 11.0 as {@code Objects.ToStringHelper.addValue()}).
*/
@CanIgnoreReturnValue
public ToStringHelper addValue(long value) {
return addHolder(String.valueOf(value));
}
/**
* Returns a string in the format specified by {@link MoreObjects#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) {
Object value = valueHolder.value;
if (!omitNullValuesSnapshot || value != null) {
builder.append(nextSeparator);
nextSeparator = ", ";
if (valueHolder.name != null) {
builder.append(valueHolder.name).append('=');
}
if (value != null && value.getClass().isArray()) {
Object[] objectArray = {value};
String arrayString = Arrays.deepToString(objectArray);
builder.append(arrayString, 1, arrayString.length() - 1);
} else {
builder.append(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 {
@Nullable String name;
@Nullable Object value;
@Nullable ValueHolder next;
}
}
private MoreObjects() {}
}