Below is the syntax highlighted version of Student.java
from §1.2 Data Abstraction.
/****************************************************************************** * Compilation: javac Student.java * Execution: java Student * Dependencies: StdOut.java * * Illustrates implementation of a Comparator and equals() method. * * % 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 * ******************************************************************************/ import java.util.Arrays; import java.util.Comparator; /** * The {@code Student} class is an immutable data type to encapsulate a * student name and section number. It is used to illustrate various * comparators. * <p> * For additional documentation, * see <a href="https://algs4.cs.princeton.edu/12oop">Section 1.2</a> of * <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne. * * @author Robert Sedgewick * @author Kevin Wayne */ public class Student { public static final Comparator<Student> NAME_ORDER = new NameOrder(); /** * A comparator for comparing students in ascending order by section number. */ public static final Comparator<Student> SECTION_ORDER = new SectionOrder(); private final String name; private final int section; /** * Initializes a new student from the given arguments. * * @param name the name of this student * @param section the section number of this student */ public Student(String name, int section) { this.name = name; this.section = section; } /** * Returns a comparator for comparing students in lexicographic order by name. * * @return a {@link Comparator} for comparing students in lexicographic order by name */ private static Comparator<Student> byNameOrder() { return new NameOrder(); } /** * Returns a comparator for comparing students in numerical order by section. * * @return a {@link Comparator} for comparing students in numerical order by section */ private static Comparator<Student> bySectionOrder() { return new SectionOrder(); } // compare students by names, starting at this student's name // and wrapping around alphabetically private Comparator<Student> byRelativeNameOrder() { return new RelativeNameOrder(); } // comparator to sort by name private static class NameOrder implements Comparator<Student> { public int compare(Student a, Student b) { return a.name.compareTo(b.name); } } // comparator to sort by section private static class SectionOrder implements Comparator<Student> { public int compare(Student a, Student 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 RelativeNameOrder implements Comparator<Student> { public int compare(Student a, Student 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); } } /** * Compares this student to the specified student. * * @param other the other student * @return {@code true} if this student equals {@code other}; * {@code false} otherwise */ @Override public boolean equals(Object other) { if (other == this) return true; if (other == null) return false; if (other.getClass() != this.getClass()) return false; Student that = (Student) other; return (this.section == that.section) && (this.name.equals(that.name)); } @Override public int hashCode() { return 31*section + name.hashCode(); } @Override public String toString() { return section + " " + name; } /** * Unit tests the {@code Student} data type. * * @param args the command-line arguments */ public static void main(String[] args) { // create an array of students Student alice = new Student("Alice", 2); Student bob = new Student("Bob", 1); Student carol = new Student("Carol", 2); Student dave = new Student("Dave", 1); Student eve = new Student("Eve", 2); Student frank = new Student("Frank", 3); Student grant = new Student("Grant", 1); Student helia = new Student("Helia", 3); Student isaac = new Student("Isaac", 3); Student jen = new Student("Jen", 1); Student kevin = new Student("Kevin", 1); Student larry = new Student("Larry", 2); Student[] 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, Student.byNameOrder()); for (int i = 0; i < students.length; i++) StdOut.println(students[i]); StdOut.println(); // now, sort by section and print results StdOut.println("By section"); StdOut.println("----------"); Arrays.sort(students, Student.bySectionOrder()); for (int i = 0; i < students.length; i++) StdOut.println(students[i]); StdOut.println(); // now, sort by name relative to Kevin StdOut.println("By Kevin"); StdOut.println("----------"); Arrays.sort(students, kevin.byRelativeNameOrder()); for (int i = 0; i < students.length; i++) StdOut.println(students[i]); StdOut.println(); Student ali = new Student("Alice", 3); String fred = "Fred"; StdOut.println("alice == ali: " + (alice == ali)); StdOut.println("alice.equals(ali): " + (alice.equals(ali))); StdOut.println("alice.equals(bob): " + (alice.equals(bob))); StdOut.println("alice.equals(fred): " + (alice.equals(fred))); } }