java.util

Class Objects

java.lang.Object

java.util.Objects

public final class Objects
extends Object

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

Since:

1.7

Method Summary

Methods

Modifier and Type	Method and Description
static <T> int	compare(T a, T b, Comparator<? super T> c) Returns 0 if the arguments are identical and c.compare(a, b) otherwise.
static boolean	deepEquals(Object a, Object b) Returns true if the arguments are deeply equal to each other and false otherwise.
static boolean	equals(Object a, Object b) Returns true if the arguments are equal to each other and false otherwise.
static int	hash(Object... values) Generates a hash code for a sequence of input values.
static int	hashCode(Object o) Returns the hash code of a non-null argument and 0 for a null argument.
static <T> T	requireNonNull(T obj) Checks that the specified object reference is not null.
static <T> T	requireNonNull(T obj, String message) Checks that the specified object reference is not null and throws a customized NullPointerException if it is.
static String	toString(Object o) Returns the result of calling toString for a non-null argument and "null" for a null argument.
static String	toString(Object o, String nullDefault) Returns the result of calling toString on the first argument if the first argument is not null and returns the second argument otherwise.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

equals

public static boolean equals(Object a,
             Object b)

Returns 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.

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

See Also:

Object.equals(Object)

deepEquals

public static boolean deepEquals(Object a,
                 Object b)

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.

Parameters:

a - an object

b - an object to be compared with a for deep equality

Returns:

true if the arguments are deeply equal to each other and false otherwise

See Also:

Arrays.deepEquals(Object[], Object[]), equals(Object, Object)

hashCode

public static int hashCode(Object o)

Returns the hash code of a non-null argument and 0 for a null argument.

Parameters:

o - an object

Returns:

the hash code of a non-null argument and 0 for a null argument

See Also:

Object.hashCode()

hash

public static int hash(Object... values)

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);
 }
 

Warning: 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).

Parameters:

values - the values to be hashed

Returns:

a hash value of the sequence of input values

See Also:

Arrays.hashCode(Object[]), List.hashCode()

toString

public static String toString(Object o)

Returns the result of calling toString for a non-null argument and "null" for a null argument.

Parameters:

o - an object

Returns:

the result of calling toString for a non-null argument and "null" for a null argument

See Also:

Object.toString(), String.valueOf(Object)

toString

public static String toString(Object o,
              String nullDefault)

Returns the result of calling toString on the first argument if the first argument is not null and returns the second argument otherwise.

Parameters:

o - an object

nullDefault - string to return if the first argument is null

Returns:

the result of calling toString on the first argument if it is not null and the second argument otherwise.

See Also:

toString(Object)

compare

public static <T> int compare(T a,
              T b,
              Comparator<? super T> c)

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.

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.

See Also:

Comparable, Comparator

requireNonNull

public static <T> T requireNonNull(T obj)

Checks that the specified object reference is not null. This method is designed primarily for doing parameter validation in methods and constructors, as demonstrated below:

 public Foo(Bar bar) {
     this.bar = Objects.requireNonNull(bar);
 }
 

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

requireNonNull

public static <T> T requireNonNull(T obj,
                   String message)

Checks that the specified object reference is not null and throws a customized NullPointerException if it is. This method is designed primarily for doing parameter validation in methods and constructors with multiple parameters, as demonstrated below:

 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");
 }
 

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