Module java.base
Package java.util

Class 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 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 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 int checkIndex​(int index, int length)
      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 <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.

    • 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

      • 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
        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

      • 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
        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

      • 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
        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