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package algs34;
import stdlib.*;
import java.util.HashSet;
/* ***********************************************************************
* Compilation: javac PhoneNumber.java
* Execution: java PhoneNumber
* Dependencies:
*
* Immutable data type for US phone numbers, but with a broken
* overloaded implementation of equals(). By implementing equals()
* with the signature
*
* public boolean equals(PhoneNumber that)
*
* we do not override the equals() method inherited from Object.
* This causes unexpected behavior when used with java.util.HashSet.
*
* DO NOT USE THIS CLASS
*
*************************************************************************/
public final class XPhoneNumberOverload {
private final int area; // area code (3 digits)
private final int exch; // exchange (3 digits)
private final int ext; // extension (4 digits)
public XPhoneNumberOverload(int area, int exch, int ext) {
this.area = area;
this.exch = exch;
this.ext = ext;
}
// overloaded equals - don't do this
public boolean equals(XPhoneNumberOverload that) {
return (this.area == that.area) && (this.exch == that.exch) && (this.ext == that.ext);
}
// satisfies the hashCode contract
public int hashCode() {
int h = 17;
h = ext + 31 * h;
h = exch + 31 * h;
h = area + 31 * h;
return h;
}
// 0 for padding with leading 0s
public String toString() {
return String.format("(%03d) %03d-%04d", area, exch, ext);
}
public static void main(String[] args) {
XPhoneNumberOverload a = new XPhoneNumberOverload(609, 258, 4455);
XPhoneNumberOverload b = new XPhoneNumberOverload(609, 876, 5309);
XPhoneNumberOverload c = new XPhoneNumberOverload(609, 003, 5309);
XPhoneNumberOverload d = new XPhoneNumberOverload(215, 876, 5309);
XPhoneNumberOverload e = new XPhoneNumberOverload(609, 876, 5309);
Object o = e;
StdOut.format("a = %s [hashcode=%d]\n", a, a.hashCode ());
StdOut.format("b = %s [hashcode=%d]\n", b, b.hashCode ());
StdOut.format("c = %s [hashcode=%d]\n", c, c.hashCode ());
StdOut.format("d = %s [hashcode=%d]\n", d, d.hashCode ());
StdOut.format("e = %s [hashcode=%d]\n", e, e.hashCode ());
// show broken behavior when you use covariant equals with a Set
HashSet<XPhoneNumberOverload> set = new HashSet<>();
set.add(a);
set.add(b);
set.add(c);
StdOut.println("Added a, b, and c");
StdOut.println("contains a: " + set.contains(a));
StdOut.println("contains b: " + set.contains(b));
StdOut.println("contains c: " + set.contains(c));
StdOut.println("contains d: " + set.contains(d));
StdOut.println("***contains e: " + set.contains(e)); // not in set, but it should be!
StdOut.println("b == e: " + (b == e));
StdOut.println("b.equals(e): " + (b.equals(e)));
StdOut.println("o == e: " + (o == e));
StdOut.println("b.equals(o): " + (b.equals(o)));
}
}
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