Java compact1, compact2, compact3 java.util Class Objects（JDK8）

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

• 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