Re: how to search an array of objects?

John Ersatznom <j.ersatz@nowhere.invalid>
Mon, 08 Jan 2007 05:19:27 -0500
Lew wrote:

public class Student
 private String name;
 public String getName() { return name; }
 public void setName( String name ) { = name; }
 private int module;
 public int getModule() { return module; }
 public void setModule( int module ) { = module; }
 private float mark;
 public float getMark() { return mark; }
 public void setMark( float mark ) { = mark; }

Ewww. Student is a value object with no behavior and no likely
implementation changes save to add or remove fields, so it should really
just be

public class Student {
    public final String name;
    public int module; // Consider making this an object too
    public float mark; // Consider making this an int, 1-100,
                       // or even an enum with A, B, C, D, F
    public Student (String name, int module, float mark) { = name;
        this.module = module;
        this.mark = mark;

Name made final since it's used as a map key.

Of course, a student is actually likely to have marks in many classes,
which suggests

public class Student {
    public final String name;
    // And address, and GPA, and other stuff
    // equals() and hashCode() methods

public class Course { whatever } // or Module or whatever

public class SchoolInfo {
    private Map<String, Student> students;
    private Map<Student, List<Course>> whosTakingWhat;
    private Map<Course, List<Student>> whosInWhat;
    private static class StudentInCourse {
        public final Student student;
        public final Course course;
        public StudentInCourse (Student student,Course course) {
            this.student = student;
            this.course = course;
        // obvious equals() and hashCode() go here
    private Map<StudentInCourse, Integer> marks;
    // whatever

Or perhaps even:

public class Course {
    private Map<Student, Integer> marks;
    public Set<Student> getTakers () { return marks.keySet(); }
    public boolean contains (Student student) {
        return marks.containsKey(student);
     * @throws NPE if student isn't taking this course
    public int getMark (Student student) {
        return marks.get(student).intValue();
    public int setMark ...

and SchoolInfo just has Map<String, Student> students and Map<String,
Course> courses, with Course responsible for listings its students and
SchoolInfo able to supply an inner class instance giving a Set view of
the courses a given student is taking by using the objects in "courses"
and their knowledge of their students (via "contains")...

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