Objects (Java Platform SE 8 ) (original) (raw)
- 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
All Methods Static Methods Concrete Methods
Modifier and Type Method Description static 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 requireNonNull(T obj) Checks that the specified object reference is not null. static 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 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. * ### Methods inherited from class java.lang.[Object](../../java/lang/Object.html "class in java.lang") `[clone](../../java/lang/Object.html#clone--), [equals](../../java/lang/Object.html#equals-java.lang.Object-), [finalize](../../java/lang/Object.html#finalize--), [getClass](../../java/lang/Object.html#getClass--), [hashCode](../../java/lang/Object.html#hashCode--), [notify](../../java/lang/Object.html#notify--), [notifyAll](../../java/lang/Object.html#notifyAll--), [toString](../../java/lang/Object.html#toString--), [wait](../../java/lang/Object.html#wait--), [wait](../../java/lang/Object.html#wait-long-), [wait](../../java/lang/Object.html#wait-long-int-)`Method Detail
* #### equals public static boolean equals([Object](../../java/lang/Object.html "class in java.lang") a, [Object](../../java/lang/Object.html "class in java.lang") 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](../../java/lang/Object.html#equals-java.lang.Object-) 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)](../../java/lang/Object.html#equals-java.lang.Object-) * #### deepEquals public static boolean deepEquals([Object](../../java/lang/Object.html "class in java.lang") a, [Object](../../java/lang/Object.html "class in java.lang") 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](../../java/util/Arrays.html#deepEquals-java.lang.Object:A-java.lang.Object:A-) is used to determine equality. Otherwise, equality is determined by using the [equals](../../java/lang/Object.html#equals-java.lang.Object-) 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\[\])](../../java/util/Arrays.html#deepEquals-java.lang.Object:A-java.lang.Object:A-), [equals(Object, Object)](../../java/util/Objects.html#equals-java.lang.Object-java.lang.Object-) * #### hashCode public static int hashCode([Object](../../java/lang/Object.html "class in java.lang") 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()](../../java/lang/Object.html#hashCode--) * #### hash public static int hash([Object](../../java/lang/Object.html "class in java.lang")... 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\[\])](../../java/util/Arrays.html#hashCode-java.lang.Object:A-). This method is useful for implementing [Object.hashCode()](../../java/lang/Object.html#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)](../../java/util/Objects.html#hashCode-java.lang.Object-). Parameters: `values` \- the values to be hashed Returns: a hash value of the sequence of input values See Also: [Arrays.hashCode(Object\[\])](../../java/util/Arrays.html#hashCode-java.lang.Object:A-), [List.hashCode()](../../java/util/List.html#hashCode--) * #### toString public static [String](../../java/lang/String.html "class in java.lang") toString([Object](../../java/lang/Object.html "class in java.lang") 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()](../../java/lang/Object.html#toString--), [String.valueOf(Object)](../../java/lang/String.html#valueOf-java.lang.Object-) * #### toString public static [String](../../java/lang/String.html "class in java.lang") toString([Object](../../java/lang/Object.html "class in java.lang") o, [String](../../java/lang/String.html "class in java.lang") 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)](../../java/util/Objects.html#toString-java.lang.Object-) * #### compare public static <T> int compare(T a, T b, [Comparator](../../java/util/Comparator.html "interface in java.util")<? 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](../../java/util/Comparator.html "interface in java.util") 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](../../java/lang/Comparable.html "interface in java.lang"), [Comparator](../../java/util/Comparator.html "interface in java.util") * #### 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](../../java/lang/NullPointerException.html "class in java.lang")` \- if `obj` is `null` * #### requireNonNull public static <T> T requireNonNull(T obj, [String](../../java/lang/String.html "class in java.lang") message) Checks that the specified object reference is not `null` and throws a customized [NullPointerException](../../java/lang/NullPointerException.html "class in java.lang") 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](../../java/lang/NullPointerException.html "class in java.lang")` \- if `obj` is `null` * #### isNull public static boolean isNull([Object](../../java/lang/Object.html "class in java.lang") obj) Returns `true` if the provided reference is `null` otherwise returns `false`. API Note: This method exists to be used as a[Predicate](../../java/util/function/Predicate.html "interface in java.util.function"), `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](../../java/util/function/Predicate.html "interface in java.util.function") * #### nonNull public static boolean nonNull([Object](../../java/lang/Object.html "class in java.lang") obj) Returns `true` if the provided reference is non-`null` otherwise returns `false`. API Note: This method exists to be used as a[Predicate](../../java/util/function/Predicate.html "interface in java.util.function"), `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](../../java/util/function/Predicate.html "interface in java.util.function") * #### requireNonNull public static <T> T requireNonNull(T obj, [Supplier](../../java/util/function/Supplier.html "interface in java.util.function")<[String](../../java/lang/String.html "class in java.lang")> messageSupplier) Checks that the specified object reference is not `null` and throws a customized [NullPointerException](../../java/lang/NullPointerException.html "class in java.lang") if it is. Unlike the method [requireNonNull(Object, String)](../../java/util/Objects.html#requireNonNull-T-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. 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](../../java/lang/NullPointerException.html "class in java.lang")` \- if `obj` is `null` Since: 1.8
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