/*
 
* Copyright (c) 2009, 2013, Oracle and/or its affiliates. All rights reserved.
 
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 
*
 
* This code is free software; you can redistribute it and/or modify it
 
* under the terms of the GNU General Public License version 2 only, as
 
* published by the Free Software Foundation.
  
Oracle designates this
 
* particular file as subject to the "Classpath" exception as provided
 
* by Oracle in the LICENSE file that accompanied this code.
 
*
 
* This code is distributed in the hope that it will be useful, but WITHOUT
 
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 
* FITNESS FOR A PARTICULAR PURPOSE.
  
See the GNU General Public License
 
* version 2 for more details (a copy is included in the LICENSE file that
 
* accompanied this code).
 
*
 
* You should have received a copy of the GNU General Public License version
 
* 2 along with this work; if not, write to the Free Software Foundation,
 
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 
*
 
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 
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*/

package java.util;

import java.util.function.Supplier;

/**
 
* This class consists of {@code static} utility methods for operating
 
* on objects.
  
These utilities include {@code null}-safe or {@code
 
* null}-tolerant methods for computing the hash code of an object,
 
* returning a string for an object, and comparing two objects.
 
*
 
* @since 1.7
 
*/

public final class Objects {
    
private Objects() {
        
throw new AssertionError("No java.util.Objects instances for you!");
    
}

    
/**
     
* Returns {@code true} if the arguments are equal to each other
     
* and {@code false} otherwise.
     
* Consequently, if both arguments are {@code null}, {@code true}
     
* is returned and if exactly one argument is {@code null}, {@code
     
* false} is returned.
  
Otherwise, equality is determined by using
     
* the {@link Object#equals equals} method of the first
     
* argument.
     
*
     
* @param a an object
     
* @param b an object to be compared with {@code a} for equality
     
* @return {@code true} if the arguments are equal to each other
     
* and {@code false} otherwise
     
* @see Object#equals(Object)
     
*/

    
public static boolean equals(Object a, Object b) {
        
return (a == b) || (a != null && a.equals(b));
    
}

   
/**
    
* Returns {@code true} if the arguments are deeply equal to each other
    
* and {@code false} otherwise.
    
*
    
* Two {@code null} values are deeply equal.
  
If both arguments are
    
* arrays, the algorithm in {@link Arrays#deepEquals(Object[],
    
* Object[]) Arrays.deepEquals} is used to determine equality.
    
* Otherwise, equality is determined by using the {@link
    
* Object#equals equals} method of the first argument.
    
*
    
* @param a an object
    
* @param b an object to be compared with {@code a} for deep equality
    
* @return {@code true} if the arguments are deeply equal to each other
    
* and {@code false} otherwise
    
* @see Arrays#deepEquals(Object[], Object[])
    
* @see Objects#equals(Object, Object)
    
*/

    
public static boolean deepEquals(Object a, Object b) {
        
if (a == b)
            
return true;
        
else if (a == null || b == null)
            
return false;
        
else
            
return
Arrays.deepEquals0(a, b);
    
}

    
/**
     
* Returns the hash code of a non-{@code null} argument and 0 for
     
* a {@code null} argument.
     
*
     
* @param o an object
     
* @return the hash code of a non-{@code null} argument and 0 for
     
* a {@code null} argument
     
* @see Object#hashCode
     
*/

    
public static int hashCode(Object o) {
        
return o != null ? o.hashCode() : 0;
    
}

   
/**
    
* Generates a hash code for a sequence of input values. The hash
    
* code is generated as if all the input values were placed into an
    
* array, and that array were hashed by calling {@link
    
* Arrays#hashCode(Object[])}.
    
*
    
* <p>This method is useful for implementing {@link
    
* Object#hashCode()} on objects containing multiple fields. For
    
* example, if an object that has three fields, {@code x}, {@code
    
* y}, and {@code z}, one could write:
    
*
    
* <blockquote><pre>
    
* &#064;Override public int hashCode() {
    
*
     
return Objects.hash(x, y, z);
    
* }
    
* </pre></blockquote>
    
*
    
* <b>Warning: When a single object reference is supplied, the returned
    
* value does not equal the hash code of that object reference.</b> This
    
* value can be computed by calling {@link #hashCode(Object)}.
    
*
    
* @param values the values to be hashed
    
* @return a hash value of the sequence of input values
    
* @see Arrays#hashCode(Object[])
    
* @see List#hashCode
    
*/

    
public static int hash(Object... values) {
        
return Arrays.hashCode(values);
    
}

    
/**
     
* Returns the result of calling {@code toString} for a non-{@code
     
* null} argument and {@code "null"} for a {@code null} argument.
     
*
     
* @param o an object
     
* @return the result of calling {@code toString} for a non-{@code
     
* null} argument and {@code "null"} for a {@code null} argument
     
* @see Object#toString
     
* @see String#valueOf(Object)
     
*/

    
public static String toString(Object o) {
        
return String.valueOf(o);
    
}

    
/**
     
* Returns the result of calling {@code toString} on the first
     
* argument if the first argument is not {@code null} and returns
     
* the second argument otherwise.
     
*
     
* @param o an object
     
* @param nullDefault string to return if the first argument is
     
*
        
{@code null}
     
* @return the result of calling {@code toString} on the first
     
* argument if it is not {@code null} and the second argument
     
* otherwise.
     
* @see Objects#toString(Object)
     
*/

    
public static String toString(Object o, String nullDefault) {
        
return (o != null) ? o.toString() : nullDefault;
    
}

    
/**
     
* Returns 0 if the arguments are identical and {@code
     
* c.compare(a, b)} otherwise.
     
* Consequently, if both arguments are {@code null} 0
     
* is returned.
     
*
     
* <p>Note that if one of the arguments is {@code null}, a {@code
     
* NullPointerException} may or may not be thrown depending on
     
* what ordering policy, if any, the {@link Comparator Comparator}
     
* chooses to have for {@code null} values.
     
*
     
* @param <T> the type of the objects being compared
     
* @param a an object
     
* @param b an object to be compared with {@code a}
     
* @param c the {@code Comparator} to compare the first two arguments
     
* @return 0 if the arguments are identical and {@code
     
* c.compare(a, b)} otherwise.
     
* @see Comparable
     
* @see Comparator
     
*/

    
public static <T> int compare(T a, T b, Comparator<? super T> c) {
        
return (a == b) ? 0 :
  
c.compare(a, b);
    
}

    
/**
     
* Checks that the specified object reference is not {@code null}. This
     
* method is designed primarily for doing parameter validation in methods
     
* and constructors, as demonstrated below:
     
* <blockquote><pre>
     
* public Foo(Bar bar) {
     
*this.bar = Objects.requireNonNull(bar);
     
* }
     
* </pre></blockquote>
     
*
     
* @param obj the object reference to check for nullity
     
* @param <T> the type of the reference
     
* @return {@code obj} if not {@code null}
     
* @throws NullPointerException if {@code obj} is {@code null}
     
*/

    
public static <T> T requireNonNull(T obj) {
        
if (obj == null)
            
throw new NullPointerException();
        
return obj;
    
}

    
/**
     
* Checks that the specified object reference is not {@code null} and
     
* throws a customized {@link NullPointerException} if it is. This method
     
* is designed primarily for doing parameter validation in methods and
     
* constructors with multiple parameters, as demonstrated below:
     
* <blockquote><pre>
     
* public Foo(Bar bar, Baz baz) {
     
*this.bar = Objects.requireNonNull(bar, "bar must not be null");
     
*this.baz = Objects.requireNonNull(baz, "baz must not be null");
     
* }
     
* </pre></blockquote>
     
*
     
* @param objthe object reference to check for nullity
     
* @param message detail message to be used in the event that a {@code
     
*
                
NullPointerException} is thrown
     
* @param <T> the type of the reference
     
* @return {@code obj} if not {@code null}
     
* @throws NullPointerException if {@code obj} is {@code null}
     
*/

    
public static <T> T requireNonNull(T obj, String message) {
        
if (obj == null)
            
throw new NullPointerException(message);
        
return obj;
    
}

    
/**
     
* Returns {@code true} if the provided reference is {@code null} otherwise
     
* returns {@code false}.
     
*
     
* @apiNote This method exists to be used as a
     
*
 
, {@code filter(Objects::isNull)}
     
*
     
* @param obj a reference to be checked against {@code null}
     
* @return {@code true} if the provided reference is {@code null} otherwise
     
* {@code false}
     
*
     
*
 

     
* @since 1.8
     
*/

    
public static boolean isNull(Object obj) {
        
return obj == null;
    
}

    
/**
     
* Returns {@code true} if the provided reference is non-{@code null}
     
* otherwise returns {@code false}.
     
*
     
* @apiNote This method exists to be used as a
     
*
 
, {@code filter(Objects::nonNull)}
     
*
     
* @param obj a reference to be checked against {@code null}
     
* @return {@code true} if the provided reference is non-{@code null}
     
* otherwise {@code false}
     
*
     
*
 

     
* @since 1.8
     
*/

    
public static boolean nonNull(Object obj) {
        
return obj != null;
    
}

    
/**
     
* Checks that the specified object reference is not {@code null} and
     
* throws a customized {@link NullPointerException} if it is.
     
*
     
* <p>Unlike the method {@link #requireNonNull(Object, String)},
     
* this method allows creation of the message to be deferred until
     
* after the null check is made. While this may confer a
     
* performance advantage in the non-null case, when deciding to
     
* call this method care should be taken that the costs of
     
* creating the message supplier are less than the cost of just
     
* creating the string message directly.
     
*
     
* @param objthe object reference to check for nullity
     
* @param messageSupplier supplier of the detail message to be
     
* used in the event that a {@code NullPointerException} is thrown
     
* @param <T> the type of the reference
     
* @return {@code obj} if not {@code null}
     
* @throws NullPointerException if {@code obj} is {@code null}
     
* @since 1.8
     
*/

    
public static <T> T requireNonNull(T obj, Supplier<String> messageSupplier) {
        
if (obj == null)
            
throw new NullPointerException(messageSupplier.get());
        
return obj;
    
}
}