Java Arrays. asList usage, javaarrays. aslist

Java Arrays. asList usage, javaarrays. aslist

1. Import java. util. Arrays;
2. Import java. util. List;
4. /**
5. *
6. * This class demonstrates the asList method in the Arrays class.
7. * Four paragraphs are used to demonstrate the features of the method.
8. *
9. * (1) this method does not support arrays of the basic data type. It is not recommended when arrays are of the basic data type.
10. * (2) when the asList () method is used, the array is linked with the list.
11. * When one of the updates is made, the other will automatically get the updates.
12. * Note: The basic data type array does not have this attribute only for the object array type.
13. * (3) the array obtained by asList does not have the add or remove methods.
14. *
15. * Reading: You can check the source code of the Arrays class. The List returned by asList is implemented in Array.
16. * Internal class, but this class does not define the add and remove methods. In addition, why modify one of them, the other is automatically
17. * Updated, because the asList obtains the List and actually references the array.
18. */
19. Public class AsListTest {
21. Public static void main (String [] args ){
23. /* Section 1: problems in using asList for basic data types */
25. /* Note: Although JDK1.6 can convert an array of the basic data type to a List, it still has a defect */
26. Int [] a_int = {1, 2, 3, 4 };
27. /* The expected output should be 1, 2, 3, 4, but the output is actually just a reference. Here it treats a_int as an element */
28. List a_int_List = Arrays. asList (a_int );
29. Foreach (a_int_List );
30. /* For this reason, we need to traverse the elements in this way */
31. ForeachForBase (a_int_List );
33. /* Section 2: Use asList for an array of object types as expected */
34. Integer [] a_Integer = new Integer [] {1, 2, 3, 4 };
35. List a_Integer_List = Arrays. asList (a_Integer );
36. Foreach (a_Integer_List );
38. /* Section 3: When the List after the array or asList is updated, the other will automatically get the update */
39. A_Integer_List.set (0, 0 );
40. Foreach (a_Integer_List );
41. Foreach (a_Integer );
43. A_Integer [0] = 5;
44. Foreach (a_Integer_List );
45. Foreach (a_Integer );
47. /* Section 4: For an array of basic types, after modifying the corresponding value in the List after asList, an exception is reported during running.
48. * However, the List corresponding to the basic type array will change, which is undoubtedly
49. */
51. /*
52. * A_int_List.set (0, 0 );
53. * Foreach (a_int_List); foreach (a_int );
54. */
56. A_int [0] = 5;
57. ForeachForBase (a_int_List );
58. Foreach (a_int );
60. }
62. /* Print method */
63. Private static void foreach (List list ){
64. For (Object object: list ){
65. System. out. print (object + "");
66. }
67. System. out. println ();
69. }
71. Private static void foreachForBase (List a_int_List ){
72. Int [] _ a_int = (int []) a_int_List.get (0 );
73. Foreach (_ a_int );
74. }
76. Private static void foreach (int [] a_int ){
77. For (int I: a_int ){
78. System. out. print (I + "");
79. }
80. System. out. println ();
81. }
83. Private static void foreach (Integer [] _ a_Integer ){
84. For (int I: _ a_Integer ){
85. System. out. print (I + "");
86. }
87. System. out. println ();
88. }
89. }