Java.util.Objects class in Java

Java 7 has come up with a new class Objects that have 9 static utility methods for operating on objects. These utilities include null-safe methods for computing the hash code of an object, returning a string for an object, and comparing two objects.

Using Objects class methods, one can smartly handle NullPointerException and can also show customized NullPointerException message(if an Exception occur).

1. String toString(Object o) : This method returns the result of calling toString() method for a non-null argument and “null” for a null argument.

   Syntax : 
   public static String toString(Object o)
   Parameters : 
   o - an object
   Returns :
   the result of calling toString() method for a non-null argument and 
   "null" for a null argument
   

2. String toString(Object o, String nullDefault) : This method is overloaded version of above method. It returns the result of calling toString() method on the first argument if the first argument is not null and returns the second argument otherwise.

   Syntax : 
   public static String toString(Object o, String nullDefault)
   Parameters : 
   o - an object
   nullDefault - string to return if the first argument is null
   Returns :
   the result of calling toString() method on the first argument if it is not null and
   the second argument otherwise.
   

   // Java program to demonstrate Objects.toString(Object o)
   // and Objects.toString(Object o, String nullDefault) methods
   
   import java.util.Objects;
   
   class Pair<K, V>
   {
       public K key;
       public V value;
   
       public Pair(K key, V value)
       {
           this.key = key;
           this.value = value;
       }
   
       @Override
       public String toString() {
           return "Pair {key = " + Objects.toString(key) + ", value = " +
                       Objects.toString(value, "no value") + "}";
   
           /* without Objects.toString(Object o) and
            Objects.toString(Object o, String nullDefault) method
            return "Pair {key = " + (key == null ? "null" : key.toString()) +
        ", value = " + (value == null ? "no value" : value.toString()) + "}"; */
       }
   }
   
   class GFG
   {
       public static void main(String[] args)
       {
           Pair<String, String> p1 =
                           new Pair<String, String>("GFG", "geeksforgeeks.org");
           Pair<String, String> p2 = new Pair<String, String>("Code", null);
   
           System.out.println(p1);
           System.out.println(p2);
       }
   }

   Output:

   Pair {key = GFG, value = geeksforgeeks.org}
   Pair {key = Code, value = no value}
   

3. boolean equals(Object a,Object b) : This method true if the arguments are equal to each other and false otherwise. Consequently, if both arguments are null, true is returned and if exactly one argument is null, false is returned. Otherwise, equality is determined by using the equals() method of the first argument.

   Syntax : 
   public static boolean equals(Object a,Object b)
   Parameters : 
   a - an object
   b - an object to be compared with a for equality
   Returns :
   true if the arguments are equal to each other and false otherwise
   

   // Java program to demonstrate equals(Object a, Object b) method
   
   import java.util.Objects;
   
   class Pair<K, V>
   {
       public K key;
       public V value;
   
       public Pair(K key, V value)
       {
           this.key = key;
           this.value = value;
       }
   
       @Override
       public boolean equals(Object o)
       {
           if (!(o instanceof Pair)) {
               return false;
           }
           Pair<?, ?> p = (Pair<?, ?>) o;
           return Objects.equals(p.key, key) && Objects.equals(p.value, value);
   
       }
   }
   
   class GFG
   {
       public static void main(String[] args)
       {
           Pair<String, String> p1 =
                   new Pair<String, String>("GFG", "geeksforgeeks.org");
   
           Pair<String, String> p2 =
                   new Pair<String, String>("GFG", "geeksforgeeks.org");
   
           Pair<String, String> p3 =
                   new Pair<String, String>("GFG", "www.geeksforgeeks.org");
   
           System.out.println(p1.equals(p2));
           System.out.println(p2.equals(p3));
   
       }
   }

   Output:

   true
   false
   

4. boolean deepEquals(Object a,Object b) :This method returns true if the arguments are deeply equal to each other and false otherwise. Two null values are deeply equal. If both arguments are arrays, the algorithm in Arrays.deepEquals is used to determine equality. Otherwise, equality is determined by using the equals method of the first argument.

   Syntax : 
   public static boolean deepEquals(Object a,Object b)
   Parameters : 
   a - an object
   b - an object to be compared with a for equality
   Returns :
   true if the arguments are deeply equals to each other and false otherwise
   

5. T requireNonNull(T obj) : This method checks that the specified object reference is not null. This method is designed primarily for doing parameter validation in methods and constructors, as demonstrated in below example:

   Syntax : 
   public static  T requireNonNull(T obj)
   Type Parameters:
   T - the type of the reference
   Parameters : 
   obj - the object reference to check for nullity
   Returns :
   obj if not null
   Throws:
   NullPointerException - if obj is null
   

6. T requireNonNull(T obj,String message) : This method is overloaded version of above method with customized message printing if obj is null as demonstrated in below example:

   Syntax : 
   public static  T requireNonNull(T obj,String message)
   Type Parameters:
   T - the type of the reference
   Parameters : 
   obj - the object reference to check for nullity
   message - detail message to be used in the event that a NullPointerException is thrown
   Returns :
   obj if not null
   Throws:
   NullPointerException - if obj is null
   

   // Java program to demonstrate Objects.requireNonNull(Object o)
   // and Objects.requireNonNull(Object o, String message) methods
   
   import java.util.Objects;
   
   class Pair<K, V>
   {
       public K key;
       public V value;
   
       public Pair(K key, V value)
       {
           this.key = key;
           this.value = value;
       }
   
       public void setKey(K key) {
           this.key = Objects.requireNonNull(key);
       }
   
       public void setValue(V value) {
           this.value = Objects.requireNonNull(value, "no value");
       }
   }
   
   class GFG
   {
       public static void main(String[] args)
       {
           Pair<String, String> p1 =
                       new Pair<String, String>("GFG", "geeksforgeeks.org");
   
           p1.setKey("Geeks");
   
           // below statement will throw NPE with customized message
           p1.setValue(null);
   
       }
   }

   Output:

   Exception in thread "main" java.lang.NullPointerException: no value
       at java.util.Objects.requireNonNull(Objects.java:228)
       at Pair.setValue(GFG.java:22)
       at GFG.main(GFG.java:36)
   

7. int hashCode(Object o) : This method returns the hash code of a non-null argument and 0 for a null argument.

   Syntax : 
   public static int hashCode(Object o)
   Parameters : 
   o - an object
   Returns :
   the hash code of a non-null argument and 0 for a null argument
   

   // Java program to demonstrate Objects.hashCode(Object o) object
   
   import java.util.Objects;
   
   class Pair<K, V>
   {
       public K key;
       public V value;
   
       public Pair(K key, V value)
       {
           this.key = key;
           this.value = value;
       }
   
       @Override
       public int hashCode()
       {
           return (Objects.hashCode(key) ^ Objects.hashCode(value));
   
           /* without Objects.hashCode(Object o) method
           return (key == null ? 0 : key.hashCode()) ^
           (value == null ? 0 : value.hashCode()); */
       }
   }
   
   class GFG
   {
       public static void main(String[] args)
       {
           Pair<String, String> p1 =
                   new Pair<String, String>("GFG", "geeksforgeeks.org");
           Pair<String, String> p2 =
                   new Pair<String, String>("Code", null);
           Pair<String, String> p3 = new Pair<String, String>(null, null);
   
           System.out.println(p1.hashCode());
           System.out.println(p2.hashCode());
           System.out.println(p3.hashCode());
       }
   }

   Output:

   450903651
   2105869
   0
   

8. int hash(Object… values) : This method 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 Arrays.hashCode(Object[]).
   This method is useful for implementing Object.hashCode() on objects containing multiple fields. For example, if an object that has three fields, x, y, and z, one could write:

   @Override 
   public int hashCode() {
        return Objects.hash(x, y, z);
   }
   

   Note: When a single object reference is supplied, the returned value does not equal the hash code of that object reference. This value can be computed by calling hashCode(Object).

   Syntax : 
   public static int hash(Object... values)
   Parameters : 
   values - the values to be hashed
   Returns :
   a hash value of the sequence of input values
   

   // Java program to demonstrate Objects.hashCode(Object o) object
   
   import java.util.Objects;
   
   class Pair<K, V>
   {
       public K key;
       public V value;
   
       public Pair(K key, V value)
       {
           this.key = key;
           this.value = value;
       }
   
       @Override
       public int hashCode()
       {
           return (Objects.hash(key,value));
       }
   }
   
   class GFG
   {
       public static void main(String[] args)
       {
           Pair<String, String> p1 =
                   new Pair<String, String>("GFG", "geeksforgeeks.org");
           Pair<String, String> p2 =
                   new Pair<String, String>("Code", null);
           Pair<String, String> p3 = new Pair<String, String>(null, null);
   
           System.out.println(p1.hashCode());
           System.out.println(p2.hashCode());
           System.out.println(p3.hashCode());
       }
   }

   Output:

   453150372
   65282900
   961
   

9. int compare(T a,T b,Comparator c) : As usual, this method returns 0 if the arguments are identical and c.compare(a, b) otherwise. Consequently, if both arguments are null 0 is returned.

   Note that if one of the arguments is null, a NullPointerException may or may not be thrown depending on what ordering policy, if any, the Comparator chooses to have for null values.

   Syntax : 
   public static  int compare(T a,T b,Comparator c)
   Type Parameters:
   T - the type of the objects being compared
   Parameters : 
   a - an object
   b - an object to be compared with a
   c - the Comparator to compare the first two arguments
   Returns :
   0 if the arguments are identical and c.compare(a, b) otherwise.
   

Note : In Java 8, Objects class has 3 more methods. Two of them(isNull(Object o) and nonNull(Object o)) are used for checking null reference. The third one is one more overloaded version of requireNonNull method. Refer here.