java8.util

Class Objects

java.lang.Object

java8.util.Objects

public final class Objects
extends Object

This class consists of static utility methods for operating on objects, or checking certain conditions before operation. These utilities include null-safe or null-tolerant methods for computing the hash code of an object, returning a string for an object, comparing two objects, and checking if indexes or sub-range values are out-of-bounds.

API Note:
Static methods such as checkIndex(int, int), checkFromToIndex(int, int, int), and checkFromIndexSize(int, int, int) are provided for the convenience of checking if values corresponding to indexes and sub-ranges are out-of-bounds. Variations of these static methods support customization of the runtime exception, and corresponding exception detail message, that is thrown when values are out-of-bounds. Such methods accept a functional interface argument, instances of BiFunction, that maps out-of-bound values to a runtime exception. Care should be taken when using such methods in combination with an argument that is a lambda expression, method reference or class that capture values. In such cases the cost of capture, related to functional interface allocation, may exceed the cost of checking bounds.

Since:

1.7

Method Summary

Modifier and Type	Method and Description
static int	checkFromIndexSize(int fromIndex, int size, int length) Checks if the sub-range from fromIndex (inclusive) to fromIndex + size (exclusive) is within the bounds of range from 0 (inclusive) to length (exclusive).
static <X extends RuntimeException> int	checkFromIndexSize(int fromIndex, int size, int length, BiFunction<String,List<Integer>,X> oobef) Checks if the sub-range from fromIndex (inclusive) to fromIndex + size (exclusive) is within the bounds of range from 0 (inclusive) to length (exclusive).
static int	checkFromToIndex(int fromIndex, int toIndex, int length) Checks if the sub-range from fromIndex (inclusive) to toIndex (exclusive) is within the bounds of range from 0 (inclusive) to length (exclusive).
static <X extends RuntimeException> int	checkFromToIndex(int fromIndex, int toIndex, int length, BiFunction<String,List<Integer>,X> oobef) Checks if the sub-range from fromIndex (inclusive) to toIndex (exclusive) is within the bounds of range from 0 (inclusive) to length (exclusive).
static int	checkIndex(int index, int length) Checks if the index is within the bounds of the range from 0 (inclusive) to length (exclusive).
static <X extends RuntimeException> int	checkIndex(int index, int length, BiFunction<String,List<Integer>,X> oobef) Checks if the index is within the bounds of the range from 0 (inclusive) to length (exclusive).
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 <X extends RuntimeException> BiFunction<String,List<Integer>,X>	outOfBoundsExceptionFormatter(Function<String,X> f) Returns an out-of-bounds exception formatter from an given exception factory.
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 <T> T	requireNonNullElse(T obj, T defaultObj) Returns the first argument if it is non-null and otherwise returns the non-null second argument.
static <T> T	requireNonNullElseGet(T obj, Supplier<? extends T> supplier) Returns the first argument if it is non-null and otherwise returns the non-null value of supplier.get().
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

isNull

public static boolean isNull(Object obj)

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

API Note:
This method exists to be used as a Predicate, filter(Objects::isNull)

Parameters:

obj - a reference to be checked against null

Returns:

true if the provided reference is null otherwise false

Since:

1.8

See Also:

Predicate

nonNull

public static boolean nonNull(Object obj)

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

API Note:
This method exists to be used as a Predicate, filter(Objects::nonNull)

Parameters:

obj - a reference to be checked against null

Returns:

true if the provided reference is non-null otherwise false

Since:

1.8

See Also:

Predicate

requireNonNullElse

public static <T> T requireNonNullElse(T obj,
                                       T defaultObj)

Returns the first argument if it is non-null and otherwise returns the non-null second argument.

Type Parameters:

T - the type of the reference

Parameters:

obj - an object

defaultObj - a non-null object to return if the first argument is null

Returns:

the first argument if it is non-null and otherwise the second argument if it is non-null

Throws:

NullPointerException - if both obj is null and defaultObj is null

Since:

9

requireNonNullElseGet

public static <T> T requireNonNullElseGet(T obj,
                                          Supplier<? extends T> supplier)

Returns the first argument if it is non-null and otherwise returns the non-null value of supplier.get().

Type Parameters:

T - the type of the first argument and return type

Parameters:

obj - an object

supplier - of a non-null object to return if the first argument is null

Returns:

the first argument if it is non-null and otherwise the value from supplier.get() if it is non-null

Throws:

NullPointerException - if both obj is null and either the supplier is null or the supplier.get() value is null

Since:

9

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(Object, 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.

Type Parameters:

T - the type of the reference

Parameters:

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

Returns:

obj if not null

Throws:

NullPointerException - if obj is null

Since:

1.8

outOfBoundsExceptionFormatter

public static <X extends RuntimeException> BiFunction<String,List<Integer>,X> outOfBoundsExceptionFormatter(Function<String,X> f)

Returns an out-of-bounds exception formatter from an given exception factory. The exception formatter is a function that formats an out-of-bounds message from its arguments and applies that message to the given exception factory to produce and relay an exception.

The exception formatter accepts two arguments: a String describing the out-of-bounds range check that failed, referred to as the check kind; and a List<Integer> containing the out-of-bound integer values that failed the check. The list of out-of-bound values is not modified.

Three check kinds are supported checkIndex, checkFromToIndex and checkFromIndexSize corresponding respectively to the specified application of an exception formatter as an argument to the out-of-bounds range check methods checkIndex, checkFromToIndex, and checkFromIndexSize. Thus a supported check kind corresponds to a method name and the out-of-bound integer values correspond to method argument values, in order, preceding the exception formatter argument (similar in many respects to the form of arguments required for a reflective invocation of such a range check method).

Formatter arguments conforming to such supported check kinds will produce specific exception messages describing failed out-of-bounds checks. Otherwise, more generic exception messages will be produced in any of the following cases: the check kind is supported but fewer or more out-of-bounds values are supplied, the check kind is not supported, the check kind is null, or the list of out-of-bound values is null.

API Note:
This method produces an out-of-bounds exception formatter that can be passed as an argument to any of the supported out-of-bounds range check methods declared by Objects. For example, a formatter producing an ArrayIndexOutOfBoundsException may be produced and stored on a static final field as follows:

 static final
 BiFunction<String, List<Integer>, ArrayIndexOutOfBoundsException> AIOOBEF =
     outOfBoundsExceptionFormatter(ArrayIndexOutOfBoundsException::new);
 

The formatter instance AIOOBEF may be passed as an argument to an out-of-bounds range check method, such as checking if an index is within the bounds of a limit:

 checkIndex(index, limit, AIOOBEF);
 

If the bounds check fails then the range check method will throw an ArrayIndexOutOfBoundsException with an appropriate exception message that is a produced from AIOOBEF as follows:

 AIOOBEF.apply("checkIndex", Arrays.asList(index, limit));
 

Type Parameters:

X - the type of runtime exception to be returned by the given exception factory and relayed by the exception formatter

Parameters:

f - the exception factory, that produces an exception from a message where the message is produced and formatted by the returned exception formatter. If this factory is stateless and side-effect free then so is the returned formatter. Exceptions thrown by the factory are relayed to the caller of the returned formatter.

Returns:

the out-of-bounds exception formatter

Since:

9

checkIndex

public static int checkIndex(int index,
                             int length)

Checks if the index is within the bounds of the range from 0 (inclusive) to length (exclusive).

The index is defined to be out-of-bounds if any of the following inequalities is true:

• index < 0
• index >= length
• length < 0, which is implied from the former inequalities

This method behaves as if checkIndex(int, int, BiFunction) was called with same out-of-bounds arguments and an exception formatter argument produced from an invocation of outOfBoundsExceptionFormatter(IndexOutOfBounds::new) (though it may be more efficient).

Parameters:

index - the index

length - the upper-bound (exclusive) of the range

Returns:

index if it is within bounds of the range

Throws:

IndexOutOfBoundsException - if the index is out-of-bounds

Since:

9

checkIndex

public static <X extends RuntimeException> int checkIndex(int index,
                                                          int length,
                                                          BiFunction<String,List<Integer>,X> oobef)

Checks if the index is within the bounds of the range from 0 (inclusive) to length (exclusive).

The index is defined to be out-of-bounds if any of the following inequalities is true:

• index < 0
• index >= length
• length < 0, which is implied from the former inequalities

If the index is out-of-bounds, then a runtime exception is thrown that is the result of applying the following arguments to the exception formatter: the name of this method, checkIndex; and an unmodifiable list of integers whose values are, in order, the out-of-bounds arguments index and length.

Type Parameters:

X - the type of runtime exception to throw if the arguments are out-of-bounds

Parameters:

index - the index

length - the upper-bound (exclusive) of the range

oobef - the exception formatter that when applied with this method name and out-of-bounds arguments returns a runtime exception. If null or returns null then, it is as if an exception formatter produced from an invocation of outOfBoundsExceptionFormatter(IndexOutOfBounds::new) is used instead (though it may be more efficient). Exceptions thrown by the formatter are relayed to the caller.

Returns:

index if it is within bounds of the range

Throws:

X - if the index is out-of-bounds and the exception formatter is non-null

IndexOutOfBoundsException - if the index is out-of-bounds and the exception formatter is null

Since:

9

checkFromToIndex

public static int checkFromToIndex(int fromIndex,
                                   int toIndex,
                                   int length)

Checks if the sub-range from fromIndex (inclusive) to toIndex (exclusive) is within the bounds of range from 0 (inclusive) to length (exclusive).

The sub-range is defined to be out-of-bounds if any of the following inequalities is true:

• fromIndex < 0
• fromIndex > toIndex
• toIndex > length
• length < 0, which is implied from the former inequalities

This method behaves as if checkFromToIndex(int, int, int, BiFunction) was called with same out-of-bounds arguments and an exception formatter argument produced from an invocation of outOfBoundsExceptionFormatter(IndexOutOfBounds::new) (though it may be more efficient).

Parameters:

fromIndex - the lower-bound (inclusive) of the sub-range

toIndex - the upper-bound (exclusive) of the sub-range

length - the upper-bound (exclusive) the range

Returns:

fromIndex if the sub-range within bounds of the range

Throws:

IndexOutOfBoundsException - if the sub-range is out-of-bounds

Since:

9

checkFromToIndex

public static <X extends RuntimeException> int checkFromToIndex(int fromIndex,
                                                                int toIndex,
                                                                int length,
                                                                BiFunction<String,List<Integer>,X> oobef)

Checks if the sub-range from fromIndex (inclusive) to toIndex (exclusive) is within the bounds of range from 0 (inclusive) to length (exclusive).

The sub-range is defined to be out-of-bounds if any of the following inequalities is true:

• fromIndex < 0
• fromIndex > toIndex
• toIndex > length
• length < 0, which is implied from the former inequalities

If the sub-range is out-of-bounds, then a runtime exception is thrown that is the result of applying the following arguments to the exception formatter: the name of this method, checkFromToIndex; and an unmodifiable list of integers whose values are, in order, the out-of-bounds arguments fromIndex, toIndex, and length.

Type Parameters:

X - the type of runtime exception to throw if the arguments are out-of-bounds

Parameters:

fromIndex - the lower-bound (inclusive) of the sub-range

toIndex - the upper-bound (exclusive) of the sub-range

length - the upper-bound (exclusive) the range

oobef - the exception formatter that when applied with this method name and out-of-bounds arguments returns a runtime exception. If null or returns null then, it is as if an exception formatter produced from an invocation of outOfBoundsExceptionFormatter(IndexOutOfBounds::new) is used instead (though it may be more efficient). Exceptions thrown by the formatter are relayed to the caller.

Returns:

fromIndex if the sub-range within bounds of the range

Throws:

X - if the sub-range is out-of-bounds and the exception factory function is non-null

IndexOutOfBoundsException - if the sub-range is out-of-bounds and the exception factory function is null

Since:

9

checkFromIndexSize

public static int checkFromIndexSize(int fromIndex,
                                     int size,
                                     int length)

Checks if the sub-range from fromIndex (inclusive) to fromIndex + size (exclusive) is within the bounds of range from 0 (inclusive) to length (exclusive).

The sub-range is defined to be out-of-bounds if any of the following inequalities is true:

• fromIndex < 0
• size < 0
• fromIndex + size > length, taking into account integer overflow
• length < 0, which is implied from the former inequalities

This method behaves as if checkFromIndexSize(int, int, int, BiFunction) was called with same out-of-bounds arguments and an exception formatter argument produced from an invocation of outOfBoundsExceptionFormatter(IndexOutOfBounds::new) (though it may be more efficient).

Parameters:

fromIndex - the lower-bound (inclusive) of the sub-interval

size - the size of the sub-range

length - the upper-bound (exclusive) of the range

Returns:

fromIndex if the sub-range within bounds of the range

Throws:

IndexOutOfBoundsException - if the sub-range is out-of-bounds

Since:

9

checkFromIndexSize

public static <X extends RuntimeException> int checkFromIndexSize(int fromIndex,
                                                                  int size,
                                                                  int length,
                                                                  BiFunction<String,List<Integer>,X> oobef)

Checks if the sub-range from fromIndex (inclusive) to fromIndex + size (exclusive) is within the bounds of range from 0 (inclusive) to length (exclusive).

The sub-range is defined to be out-of-bounds if any of the following inequalities is true:

• fromIndex < 0
• size < 0
• fromIndex + size > length, taking into account integer overflow
• length < 0, which is implied from the former inequalities

If the sub-range is out-of-bounds, then a runtime exception is thrown that is the result of applying the following arguments to the exception formatter: the name of this method, checkFromIndexSize; and an unmodifiable list of integers whose values are, in order, the out-of-bounds arguments fromIndex, size, and length.

Type Parameters:

X - the type of runtime exception to throw if the arguments are out-of-bounds

Parameters:

fromIndex - the lower-bound (inclusive) of the sub-interval

size - the size of the sub-range

length - the upper-bound (exclusive) of the range

oobef - the exception formatter that when applied with this method name and out-of-bounds arguments returns a runtime exception. If null or returns null then, it is as if an exception formatter produced from an invocation of outOfBoundsExceptionFormatter(IndexOutOfBounds::new) is used instead (though it may be more efficient). Exceptions thrown by the formatter are relayed to the caller.

Returns:

fromIndex if the sub-range within bounds of the range

Throws:

X - if the sub-range is out-of-bounds and the exception factory function is non-null

IndexOutOfBoundsException - if the sub-range is out-of-bounds and the exception factory function is null

Since:

9