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Java.util.Objects class in Java

  • Difficulty Level : Medium
  • Last Updated : 13 Nov, 2017

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.

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