public class CreatingLinkedLists
1: //CreatingLinkedLists.java
2: //Illustrates various ways to create a LinkedList.
4: import java.util.LinkedList;
5: import java.util.Arrays;
6: import java.util.List;
7: import java.util.stream.Collectors;
8: import java.util.stream.Stream;
10: public class CreatingLinkedLists
11: {
12: public static void main(String[] args)
13: {
14: //First we create an array of integers for use in some of
15: //the following examples, and then display its values.
16: Integer[] arrayOfInteger =
17: {
18: 4, 1, 5, 3, 2
19: };
20: System.out.print("arrayOfInteger: ");
21: for (int i : arrayOfInteger)
22: {
23: System.out.print(i + " ");
24: }
25: System.out.println();
27: //1Now we create a LinkedList from the above array using
28: //the static method Arrays.asList() from the Arrays class:
29: LinkedList<Integer> linkedListOfInteger1 =
30: new LinkedList<>(Arrays.asList(arrayOfInteger));
31: System.out.println("linkedListOfInteger1: " + linkedListOfInteger1);
33: //2Next we create a LinkedList from the above array using
34: //the Java 8 Stream "collector" approach:
35: LinkedList<Integer> linkedListOfInteger2 =
36: Stream
37: .of(arrayOfInteger)
38: .collect(Collectors.toCollection(LinkedList::new));
39: System.out.println("linkedListOfInteger2: " + linkedListOfInteger2);
41: //3In this code segment the last line "proves" that if we use an
42: //interface as the type rather than the class, we still get the
43: //class object we expect.
44: List<Integer> linkedListOfInteger3 =
45: Stream
46: .of(arrayOfInteger)
47: .collect(Collectors.toCollection(LinkedList::new));
48: System.out.println("linkedListOfInteger3: " + linkedListOfInteger3);
49: System.out.println(linkedListOfInteger3.getClass().getName());
51: //4With Java 9 we can shorten the above approach to this:
52: List<Integer> linkedListOfInteger4 = List.of(4, 1, 5, 3, 2);
53: System.out.println("linkedListOfInteger4: " + linkedListOfInteger4);
54: System.out.println(linkedListOfInteger4.getClass().getName());
55: //But note that we get a somewhat different class ...
57: //5We can now also intialize an LinkedList directly with a code block:
58: LinkedList<Integer> linkedListOfInteger5 = new LinkedList<Integer>()
59: {
60: {
61: add(4);
62: add(1);
63: add(5);
64: add(3);
65: add(2);
66: }
67: };
68: System.out.println("linkedListOfInteger5: " + linkedListOfInteger5);
70: System.out.println();
72: //========================================================
73: //Exercise:
74: //Repeat what we did in the above five code segments, but
75: //with strings instead of integers, and here is a starting
76: //array of strings to use:
77: String arrayOfString[] =
78: {
79: "klm", "abc", "xyz", "pqr"
80: };
81: System.out.print("arrayOfString: ");
82: for (String s : arrayOfString)
83: {
84: System.out.print(s + " ");
85: }
86: System.out.println();
87: }
88: }
89: /* Output:
90: arrayOfInteger: 4 1 5 3 2
91: linkedListOfInteger1: [4, 1, 5, 3, 2]
92: linkedListOfInteger2: [4, 1, 5, 3, 2]
93: linkedListOfInteger3: [4, 1, 5, 3, 2]
94: java.util.LinkedList
95: linkedListOfInteger4: [4, 1, 5, 3, 2]
96: java.util.ImmutableCollections$ListN
97: linkedListOfInteger5: [4, 1, 5, 3, 2]
99: arrayOfString: klm abc xyz pqr
100: */