/**

This student object has the hashcode overridden to be the perm, 
but the .equals checks both the perm and the name.

As an exercise: is this a legal design?  Or does it
"violate the contract" of the hashCode and equals methods?

(See Chapter 16 in HFH 2nd edition)

 */

public class Student {

    private String name;
    private int perm;


    public Student(String name, int perm) {
	this.name = name;
	this.perm = perm;

    }

    public String getName() { return name; }
    public int getPerm() { return perm; }

    public boolean equals(Object o) {

	if ( o == null) return false;

	if ( ! (o instanceof Student)) return false;

	Student s = (Student) o;

	return s.getPerm() == this.getPerm() && 
	    s.getName().equals(this.getName());

    }

    public int hashCode() { return perm; }


    public static void main(String [] args) {
	Student s1 = new Student("Fred",1234567);
	Student s2 = new Student("Mary",1234567);
	Student s3 = new Student("Mary",1234567);
	Student s4 = s1;
	
	System.out.printf("       s1==s2: %b\n",s1==s2);
	System.out.printf("s1.equals(s2): %b\n",s1.equals(s2));

	System.out.printf("       s1==s3: %b\n",s1==s3);
	System.out.printf("s1.equals(s3): %b\n",s1.equals(s3));

	System.out.printf("       s1==s4: %b\n",s1==s4);
	System.out.printf("s1.equals(s4): %b\n",s1.equals(s4));

	System.out.printf("System.identityHashCode(s1)=%d\n",System.identityHashCode(s1));
	System.out.printf("System.identityHashCode(s2)=%d\n",System.identityHashCode(s2));
	System.out.printf("System.identityHashCode(s3)=%d\n",System.identityHashCode(s3));
	System.out.printf("System.identityHashCode(s4)=%d\n",System.identityHashCode(s4));

	System.out.printf("s1.hashCode()=%d\n",s1.hashCode());
	System.out.printf("s2.hashCode()=%d\n",s2.hashCode());
	System.out.printf("s3.hashCode()=%d\n",s3.hashCode());
	System.out.printf("s4.hashCode()=%d\n",s4.hashCode());


    }
}