Collections tool class (V)

Catalog

collections: operation Collection、Map Tool class of

copy Code presentation for

Interview questions ：Collection and coLLections The difference between ?

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collections: operation Collection、Map Tool class of

 The sorting operation :( Are all static Method )
>reverse(List): reverse List The order of the elements in 
>shuffle(List): Yes List Set elements in random order 
sort(List): Specify according to the natural order of the elements IList The set elements are sorted in ascending order 
sort(List, Comparator): According to the designation Comparator  The order of production is to List Set elements to sort 
swap(List,int, int): Will specify list In the collection i The elements and j Exchange elements at Ⅰ
 lookup 、 Replace 
Object max(Collection): According to the natural order of the elements , Returns the largest element in a given set 
Object max(Collection,Comparator): according to Comparator The order of designation , Returns the largest element in a given set 
Object min(Collection)
Object min(Collection,Comparator)
int frequency(Collectionl,Object): Returns the number of occurrences of a specified element in a specified collection 
void copy(List dest,List src): take src Copy the contents of to dest in 
boolean replaceAll(List list,Object oldVal,Object newVal): Replace with a new value List All old values of the object 

copy Code presentation for

 @Test
    public void test1() {
        //    void copy(List dest,List src): take src Copy the contents of to dest in 
        ArrayList arrayList = new ArrayList();
        arrayList.add(123);
        arrayList.add(354);
        arrayList.add(76);
        arrayList.add(5);
        arrayList.add(-9);
//       The abnormal ：java.lang.IndexOutOfBoundsException: Source does not fit in dest
//        ArrayList arrayList1 = new ArrayList();
//        Collections.copy(arrayList1,arrayList);
//       Correct ：
        List arrayList1 = Arrays.asList(new Object[arrayList.size()]);
        System.out.println(arrayList1.size());// Is equal to arrayList Of size
        Collections.copy(arrayList1, arrayList);
        System.out.println(arrayList1);


//        CoLlections Class provides multiple synchronizedXxx() Method , This method can wrap the specified collection into a thread synchronized collection ,
//         So it can solve the problem of thread safety when multithreading concurrent access to the collection 
        List list = Collections.synchronizedList(arrayList);
//        list It's thread safe 


    }
}

Interview questions ：Collection and coLLections The difference between ?