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StreamArrayListProcessing.java
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1 /*
2 * A program to perform some basic operations on a list of Strings
3 * using Java streams.
4 */
5
6 package arraylists;
7
8 import java.util.ArrayList;
9 import java.util.List;
10 import java.util.stream.Collectors;
11
12 public class StreamArrayListProcessing {
13
14 public static void main(String[] args) {
15 // POINT A: Add some strings which represent names to an ArrayList.
16 List<String> names = new ArrayList<>();
17 names.add("Holiday, Billie");
18 names.add("Claudel, Camille");
19 names.add("Picasso, Pablo");
20 names.add("Gallen-Kallela, Akseli");
21 names.add("Zotto, Osvaldo");
22 names.add("Oshie, TJ");
23 names.add("Carlson, John");
24 names.add("Ovechkin, Alex");
25
26 // POINT B: Use map and the toList collector to create an ArrayList of just
27 // the first names of the names ArrayList. Use a for loop to print
28 // out the names, separated by spaces.
29 List<String> firstNamesList = names.stream()
30 .map(n -> firstName(n))
31 .collect(Collectors.toList());
32 System.out.print("First names: ");
33 for (String firstName : firstNamesList) {
34 System.out.print(firstName + " ");
35 }
36 System.out.println();
37
38 // POINT C: Use map and the joining collector to create a String of just
39 // the first names of the names ArrayList with each name separated
40 // by a comma. Print it.
41 String firstNames = names.stream()
42 .map(n -> firstName(n))
43 .collect(Collectors.joining(", "));
44 System.out.println("First names: " + firstNames);
45
46 // POINT D: By analogy from point C, print a comma-separated list of the
47 // last names in the names ArrayList.
48 String lastNames = names.stream()
49 .map(n -> lastName(n))
50 .collect(Collectors.joining(", "));
51 System.out.println("Last names: " + lastNames);
52
53 // POINT E: Print a comma-separated list of all uppercase first names
54 // from the list of names in the names ArrayList.
55 String upperCaseFirstNames = names.stream()
56 .map(n -> firstName(n))
57 .map(n -> n.toUpperCase())
58 .collect(Collectors.joining(", "));
59 System.out.println("Uppercase first names: " + upperCaseFirstNames);
60
61 // POINT F: Print a comma-separated list of all hyphenated last names
62 // from the list of names in the names ArrayList.
63 String hyphenatedLastNames = names.stream()
64 .map(n -> lastName(n))
65 .filter(n -> n.contains("-"))
66 .collect(Collectors.joining(", "));
67 System.out.println("Hyphenated last names: " + hyphenatedLastNames);
68
69 // POINT G: Print the integer value of the total length of all names
70 // in the names ArrayList.
71 int totalLength = names.stream()
72 .map(n -> n.length())
73 .reduce(0, (n1, n2) -> n1 + n2);
74 System.out.println("Total length: " + totalLength);
75
76 // POINT H: Print the integer value of the total length of all
77 // first names in the names ArrayList.
78 int firstNameLength = names.stream()
79 .map(n -> firstName(n).length())
80 .reduce(0, (n1, n2) -> n1 + n2);
81 System.out.println("First name length: " + firstNameLength);
82
83 // POINT I: Print the integer value of the product of the length of
84 // all first names in the names ArrayList.
85 int productOfNameLengths = names.stream()
86 .map(n -> n.length())
87 .reduce(1, (n1, n2) -> n1 * n2);
88 System.out.println("Problem of name lengths: " + productOfNameLengths);
89 }
90
91 private static String firstName(String directoryStyleName) {
92 int comma = directoryStyleName.indexOf(",");
93 String first = directoryStyleName.substring(comma + 2);
94 return first;
95 }
96
97 private static String lastName(String directoryStyleName) {
98 int comma = directoryStyleName.indexOf(",");
99 String last = directoryStyleName.substring(0, comma);
100 return last;
101 }
102 }
103