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.

   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

   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

   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

   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

453150372
65282900
961

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.