AbstractMap.SimpleImmutableEntry (Java SE 17 & JDK 17)
Description: declaration: module: java.base, package: java.util, class: AbstractMap, class: SimpleImmutableEntry
Keywords: java.util.AbstractMap.SimpleImmutableEntry class

Module java.base
Package java.util

# Class AbstractMap.SimpleImmutableEntry<K,V>

java.lang.Object
java.util.AbstractMap.SimpleImmutableEntry<K,V>

All Implemented Interfaces:
  `Serializable`, `Map.Entry<K,V>`

Enclosing class:
  AbstractMap<K,V>

public static class AbstractMap.SimpleImmutableEntry<K,V> extends Object implements Map.Entry<K,V>, Serializable
An unmodifiable Entry maintaining a key and a value. This class does not support the `setValue` method. Instances of this class are not associated with any map's entry-set view.

API Note:
  Instances of this class are not necessarily immutable, as the key and value may be mutable. An instance of this specific class is unmodifiable, because the key and value references cannot be changed. A reference of this type may not be unmodifiable, as a subclass may be modifiable or may provide the appearance of modifiability.

  This class may be convenient in methods that return thread-safe snapshots of key-value mappings. For alternatives, see the `Map::entry` and `Map.Entry::copyOf` methods.

Since:
  1.6
See Also:
  - Serialized Form

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `SimpleImmutableEntry(Map.Entry<? extends K,? extends V> entry)`
  Creates an entry representing the same mapping as the specified entry.
  `SimpleImmutableEntry(K key, V value)`
  Creates an entry representing a mapping from the specified key to the specified value.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `boolean`
  `equals(Object o)`
  Compares the specified object with this entry for equality.
  `K`
  `getKey()`
  Returns the key corresponding to this entry.
  `V`
  `getValue()`
  Returns the value corresponding to this entry.
  `int`
  `hashCode()`
  Returns the hash code value for this map entry.
  `V`
  `setValue(V value)`
  Replaces the value corresponding to this entry with the specified value (optional operation).
  `String`
  `toString()`
  Returns a String representation of this map entry.

  ### Methods declared in class java.lang.Object

  `clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

- ## Constructor Details

  - ### SimpleImmutableEntry

    public SimpleImmutableEntry(K key, V value)
    Creates an entry representing a mapping from the specified key to the specified value.
    Parameters:
      `key` - the key represented by this entry
      `value` - the value represented by this entry

  - ### SimpleImmutableEntry

    public SimpleImmutableEntry(Map.Entry<? extends K,? extends V> entry)
    Creates an entry representing the same mapping as the specified entry.
    Parameters:
      `entry` - the entry to copy

- ## Method Details

  - ### getKey

    public K getKey()
    Returns the key corresponding to this entry.
    Specified by:
      `getKey` in interface `Map.Entry<K,V>`
    Returns:
      the key corresponding to this entry

  - ### getValue

    public V getValue()
    Returns the value corresponding to this entry.
    Specified by:
      `getValue` in interface `Map.Entry<K,V>`
    Returns:
      the value corresponding to this entry

  - ### setValue

    public V setValue(V value)
    Replaces the value corresponding to this entry with the specified value (optional operation). This implementation simply throws `UnsupportedOperationException`, as this class implements an unmodifiable map entry.
    Specified by:
      `setValue` in interface `Map.Entry<K,V>`
    Implementation Requirements:
      The implementation in this class always throws `UnsupportedOperationException`.
    Parameters:
      `value` - new value to be stored in this entry
    Returns:
      (Does not return)
    Throws:
      `UnsupportedOperationException` - always

  - ### equals

    public boolean equals(Object o)
    Compares the specified object with this entry for equality. Returns `true` if the given object is also a map entry and the two entries represent the same mapping. More formally, two entries `e1` and `e2` represent the same mapping if

           (e1.getKey()==null ?
            e2.getKey()==null :
            e1.getKey().equals(e2.getKey()))
           &&
           (e1.getValue()==null ?
            e2.getValue()==null :
            e1.getValue().equals(e2.getValue()))

    This ensures that the `equals` method works properly across different implementations of the `Map.Entry` interface.
    Specified by:
      `equals` in interface `Map.Entry<K,V>`
    Overrides:
      `equals` in class `Object`
    Parameters:
      `o` - object to be compared for equality with this map entry
    Returns:
      `true` if the specified object is equal to this map entry
    See Also:
      - `hashCode()`

  - ### hashCode

    public int hashCode()
    Returns the hash code value for this map entry. The hash code of a map entry `e` is defined to be:

           (e.getKey()==null   ? 0 : e.getKey().hashCode()) ^
           (e.getValue()==null ? 0 : e.getValue().hashCode())

    This ensures that `e1.equals(e2)` implies that `e1.hashCode()==e2.hashCode()` for any two Entries `e1` and `e2`, as required by the general contract of `Object.hashCode()`.
    Specified by:
      `hashCode` in interface `Map.Entry<K,V>`
    Overrides:
      `hashCode` in class `Object`
    Returns:
      the hash code value for this map entry
    See Also:
      - `equals(java.lang.Object)`

  - ### toString

    public String toString()
    Returns a String representation of this map entry. This implementation returns the string representation of this entry's key followed by the equals character ("`=`") followed by the string representation of this entry's value.
    Overrides:
      `toString` in class `Object`
    Returns:
      a String representation of this map entry