程序包 java.util

类 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.

从以下版本开始:

1.7

方法概要

限定符和类型	方法	说明
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 boolean	isNull(Object obj)	Returns true if the provided reference is null otherwise returns false.
static boolean	nonNull(Object obj)	Returns true if the provided reference is non-null otherwise returns false.
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 <T> T	requireNonNull(T obj, Supplier<String> messageSupplier)	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.

从类继承的方法 java.lang.Object

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

方法详细资料

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 Object#equals method of the first argument.

参数:

a - an object

b - an object to be compared with a for equality

返回:

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

另请参阅:

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(Object[], Object[]) is used to determine equality. Otherwise, equality is determined by using the Object#equals method of the first argument.

参数:

a - an object

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

返回:

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

另请参阅:

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.

参数:

o - an object

返回:

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

另请参阅:

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(java.lang.Object).

参数:

values - the values to be hashed

返回:

a hash value of the sequence of input values

另请参阅:

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.

参数:

o - an object

返回:

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

另请参阅:

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.

参数:

o - an object

nullDefault - string to return if the first argument is null

返回:

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

另请参阅:

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.

类型参数:

T - the type of the objects being compared

参数:

a - an object

b - an object to be compared with a

c - the Comparator to compare the first two arguments

返回:

0 if the arguments are identical and c.compare(a, b) otherwise.

另请参阅:

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);
 }
 

类型参数:

T - the type of the reference

参数:

obj - the object reference to check for nullity

返回:

obj if not null

抛出:

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");
 }
 

类型参数:

T - the type of the reference

参数:

obj - the object reference to check for nullity

message - detail message to be used in the event that a NullPointerException is thrown

返回:

obj if not null

抛出:

NullPointerException - if obj is null

isNull

public static boolean isNull(Object obj)

Returns true if the provided reference is null otherwise returns false.

参数:

obj - a reference to be checked against null

返回:

true if the provided reference is null otherwise false

从以下版本开始:

1.8

另请参阅:

Predicate

nonNull

public static boolean nonNull(Object obj)

Returns true if the provided reference is non-null otherwise returns false.

参数:

obj - a reference to be checked against null

返回:

true if the provided reference is non-null otherwise false

从以下版本开始:

1.8

另请参阅:

Predicate

requireNonNull

public static <T> T requireNonNull(T obj,
                                   Supplier<String> messageSupplier)

Checks that the specified object reference is not null and throws a customized NullPointerException if it is.

Unlike the method requireNonNull(java.lang.Object,java.lang.String), this method allows creation of the message to be deferred until after the null check is made. While this may confer a performance advantage in the non-null case, when deciding to call this method care should be taken that the costs of creating the message supplier are less than the cost of just creating the string message directly.

类型参数:

T - the type of the reference

参数:

obj - the object reference to check for nullity

messageSupplier - supplier of the detail message to be used in the event that a NullPointerException is thrown

返回:

obj if not null

抛出:

NullPointerException - if obj is null

从以下版本开始:

1.8