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Googgle guava ImmutableCollections

2022-07-04 11:44:00 【Brother Wang_】

Googgle guava ImmutableCollections

Reference documents

Google Guava ImmutableCollections Official documents

Immutable objects have many advantages（ Immutable classes have many benefits ）

Safe for use by untrusted libraries( Use untrusted libraries safely ), I remember Effective Java I saw , Because what is passed is a set or object , This will lead to many situations , The external may change the incoming object , Or the collection or object returned by the current class may also destroy the currently returned reference information , So protect , What you get and what you go out will not be destroyed by outsiders .
Thread-safe: can be used by many threads with no risk of race conditions.( Thread safety ： It can be used by many threads , There is no risk of competitive conditions ) Each thread gets a copy of an immutable class .
Can be used as a constant , Expect it to remain fixed .
Making immutable copies of objects is a good defense programming technique a good defensive programming technique
When you don't want to modify the set , Or expect the set to remain unchanged , It is a good practice to copy it defensively into an immutable set .

How to create immutable classes

copyOf()

       
        public static void  usingCopyOf(){
        
        Set<Integer> set = new HashSet<Integer>();
        
        set.add(1);
        
        set.add(2);
        
        ImmutableSet<Integer> immutableSet = ImmutableSet.copyOf(set);
        
        // Adding elements is not supported here 
        
        /*immutableSet.add(4);
        
        Set<Integer> addOne = new HashSet<>();
        
        addOne.add(5);
        
        immutableSet.addAll(addOne);*/
        
    }
       
       
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of()
of Methods are overloaded with many numbers , The last one is the optional extension parameter .

       
        public static void  usingOf(){
        
        ImmutableSet<Integer> ofSet = ImmutableSet.of(1,2,3,4,5,6,7);
        
        System.out.println(ofSet);
        
}
       
       
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Use builder mode to create

       
        public static  void usingBuilder(){
        
        ImmutableSet<Integer> builderSet = ImmutableSet.<Integer>builder()
        
                .add(1)
        
                .add(2)
        
                .build();
        
        System.out.println(builderSet);
        
}
        

        
  /**
        
   * Returns a new builder. The generated builder is equivalent to the builder
        
   * created by the {@link Builder} constructor.
        
   */
        
  public static <E> Builder<E> builder() {
        
    return new Builder<E>();
        
  }
       
       
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asList()
All immutable sets provide a ImmutableList View asList() Even if you have data stored as one ImmutableSortedSet, You can get k The smallest element sortedSet.asList().get(k).

Main set

Variable set type	Variable collection sources ：JDK or Guava	Guava Immutable set
Collection	JDK	ImmutableCollection
List	JDK	ImmutableList
Set	JDK	ImmutableSet
SortedSet/NavigableSet	JDK	ImmutableSortedSet
Map	JDK	ImmutableMap
SortedMap	JDK	ImmutableSortedMap
Multiset	Guava	ImmutableMultiset
SortedMultiset	Guava	ImmutableSortedMultiset
Multimap	Guava	ImmutableMultimap
ListMultimap	Guava	ImmutableListMultimap
SetMultimap	Guava	ImmutableSetMultimap
BiMap	Guava	ImmutableBiMap
ClassToInstanceMap	Guava	ImmutableClassToInstanceMap
Table	Guava	ImmutableTable