001
002
003
004
005
006
007
008
009
010
011
012
013
014
015
016
017
018
019
020
021
022
023
024
025
026
027
028
029
030
031
032
033
034
035
036
037
038
039
040
041
042
043
044
045
046
047
048
049
050
051
052
053
054
055
056
057
058
059
060
061
062
063
064
065
066
067
068
069
070
071
072
073
074
075
076
077
078
079
080
081
082
083
084
085
086
087
088
089
090
091
092
093
094
095
096
097
098
099
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
|
package algs25;
import stdlib.*;
import java.util.Arrays;
import java.util.Comparator;
/* ***********************************************************************
* Compilation: javac Student.java
* Execution: java Student
*
* Illustrates implementation of a Comparator
*
* % By name
* ----------
* 2 Alice
* 1 Bob
* 2 Carol
* 1 Dave
* 2 Eve
* 3 Frank
* 1 Grant
* 3 Helia
* 3 Isaac
* 1 Jen
* 1 Kevin
* 2 Larry
* By section
* ----------
* 1 Bob
* 1 Dave
* 1 Grant
* 1 Jen
* 1 Kevin
* 2 Alice
* 2 Carol
* 2 Eve
* 2 Larry
* 3 Frank
* 3 Helia
* 3 Isaac
*
* By Kevin
* ----------
* 1 Kevin
* 2 Larry
* 2 Alice
* 1 Bob
* 2 Carol
* 1 Dave
* 2 Eve
* 3 Frank
* 1 Grant
* 3 Helia
* 3 Isaac
* 1 Jen
*
*************************************************************************/
public class XStudent {
public static final Comparator<XStudent> BY_NAME = new ByName();
public static final Comparator<XStudent> BY_SECTION = new BySection();
public final Comparator<XStudent> BY_MY_NAME = new ByMyName();
private final String name;
private final int section;
// constructor
public XStudent(String name, int section) {
this.name = name;
this.section = section;
}
// comparator to sort by name
private static class ByName implements Comparator<XStudent> {
public int compare(XStudent a, XStudent b) {
return a.name.compareTo(b.name);
}
}
// comparator to sort by section
private static class BySection implements Comparator<XStudent> {
public int compare(XStudent a, XStudent b) {
return a.section - b.section;
}
}
// comparator to sort by name with this name first
// illustrates the use of a non-static comparator
private class ByMyName implements Comparator<XStudent> {
public int compare(XStudent a, XStudent b) {
if (a.name.compareTo(b.name) == 0) return 0;
if (a.name.compareTo(name) == 0) return -1;
if (b.name.compareTo(name) == 0) return +1;
if ((a.name.compareTo(name) < 0) && (b.name.compareTo(name) > 0))
return +1;
if ((a.name.compareTo(name) > 0) && (b.name.compareTo(name) < 0))
return -1;
return a.name.compareTo(b.name);
}
}
// return string representation
public String toString() {
return section + " " + name;
}
// test client
public static void main(String[] args) {
// create an array of students
XStudent alice = new XStudent("Alice", 2);
XStudent bob = new XStudent("Bob", 1);
XStudent carol = new XStudent("Carol", 2);
XStudent dave = new XStudent("Dave", 1);
XStudent eve = new XStudent("Eve", 2);
XStudent frank = new XStudent("Frank", 3);
XStudent grant = new XStudent("Grant", 1);
XStudent helia = new XStudent("Helia", 3);
XStudent isaac = new XStudent("Isaac", 3);
XStudent jen = new XStudent("Jen", 1);
XStudent kevin = new XStudent("Kevin", 1);
XStudent larry = new XStudent("Larry", 2);
XStudent[] students = {
larry, kevin, jen, isaac, grant, helia,
frank, eve, dave, carol, bob, alice
};
// sort by name and print results
StdOut.println("By name");
StdOut.println("----------");
Arrays.sort(students, BY_NAME);
for (XStudent student : students)
StdOut.println(student);
StdOut.println();
// now, sort by section and print results
StdOut.println("By section");
StdOut.println("----------");
Arrays.sort(students, BY_SECTION);
for (XStudent student : students)
StdOut.println(student);
StdOut.println();
// now, sort by name relative to Kevin
StdOut.println("By Kevin");
StdOut.println("----------");
Arrays.sort(students, kevin.BY_MY_NAME);
for (XStudent student : students)
StdOut.println(student);
StdOut.println();
}
}
|