Java sublist, ToArray, aslist note points

1. ArrayList's sublist

The result can not be strongly turned into ArrayList, otherwise throw classcastexception exception, because Sublist returned is ArrayList's inner class sublist, not ArrayList, but a view of ArrayList. Example

 Public class sublisttest {    publicstaticvoid  main (string[] args) {        ArrayList  New arraylist<integer>();        Mylist.add (1);        Mylist.add (2);        Mylist.add (3);        Mylist.add (4);        List<Integer> sublist = mylist.sublist (1, 2);        System.out.println (myList);        System.out.println (sublist);    }}

Output

[1, 2, 3, 4] [2]

The

operation for Sublist will eventually be reflected in the original list, such as

 Public class sublisttest {    publicstaticvoid  main (string[] args) {        ArrayList  New arraylist<integer>();        Mylist.add (1);        Mylist.add (2);        Mylist.add (3);        Mylist.add (4);        List<Integer> sublist = mylist.sublist (1, 2);        Sublist.add (5);        System.out.println (myList);        System.out.println (sublist);    }}

Results

[1, 2, 5, 3, 4] [2, 5]

Note that the modification of the original list causes the concurrentmodificationexception exception to be traversed, added, and deleted by the child list, for example

 Public class sublisttest {    publicstaticvoid  main (string[] args) {        ArrayList  New arraylist<integer>();        Mylist.add (1);        Mylist.add (2);        Mylist.add (3);        Mylist.add (4);        List<Integer> sublist = mylist.sublist (1, 2);        Mylist.add (5);        System.out.println (myList);        System.out.println (sublist);    }}

Results

Exception in thread "main" java.util.ConcurrentModificationException at    java.util.arraylist$ Sublist.checkforcomodification (arraylist.java:1237) at    Java.util.arraylist$sublist.listiterator ( arraylist.java:1097) at    java.util.AbstractList.listIterator (abstractlist.java:299)    at Java.util.arraylist$sublist.iterator (arraylist.java:1093) at    java.util.AbstractCollection.toString ( abstractcollection.java:454) at    java.lang.String.valueOf (string.java:2994)    at Java.io.PrintStream.println (printstream.java:821)    at Sublisttest.main (sublisttest.java:16) [1, 2, 3, 4, 5]

2. Set-to-go array toarray

The recommended size is list.size (). If it is less than required, ToArray will reallocate the memory space and return the array address: If the array element is greater than required, the excess will be null. Example

 Public class toarraytest {    publicstaticvoid  main (string[] args) {        List  New arraylist<integer>();        Mylist.add (1);        Mylist.add (2);        Mylist.add (3);         New integer[mylist.size ()];        Mylist.toarray (MyArray);        System.out.println (myList);        System.out.println (myarray.length);    }}

Results

[1, 2, 3]3

Note: If you use List.toarray () without parameters directly, the object[] class is returned, the classcastexception exception will occur if you force the conversion to an array

3. Using Aslist to convert an array into a set

Do not increase or delete the resulting results, or you will throw unsupportedoperationexception exceptions, for example

 Public class aslisttest {    publicstaticvoid  main (string[] args) {        new integer[] {1, 2, 3};        List<Integer> myList = arrays.aslist (myArray);        Mylist.add (2); //         Mylist.remove (4);     }}

Results

Exception in thread "main" java.lang.UnsupportedOperationException at    Java.util.AbstractList.add ( abstractlist.java:148) at    Java.util.AbstractList.add (abstractlist.java:108) at    Aslisttest.main ( Aslisttest.java:9)

Reason: Aslist returned is the inner class of arrays, and does not implement the collection of modification methods, just the embodiment of the adapter mode, only the conversion interface, the background is actually an array, so that the data to delete and deletion is certainly not possible. Since the background is an array, the modification of the element is still possible, such as

 public  class   Aslisttest { static  void   main (string[] args) {intege        r[] MyArray  = new  integer[] {1, 2, 3}; List  <Integer> myList = Arrays.aslist (MyArray);  //  Mylist.add (2);  //         Mylist.remove (4);         MYARRAY[1] = 5;        System.out.println (myarray[ 1 1

Results

55

Java sublist, ToArray, aslist note points