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Java.util.Objects class in Java - GeeksforGeeks

Java.util.Objects class in Java

Last Updated : 24 Jul, 2024

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).

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

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


   // 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}

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


   // 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

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
```

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

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


   // 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)

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


   // 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

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


   // 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

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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